diff --git a/openbsc/.gitignore b/openbsc/.gitignore
index ca73db6..fc3d0bf 100644
--- a/openbsc/.gitignore
+++ b/openbsc/.gitignore
@@ -53,6 +53,7 @@ src/utils/isdnsync
 src/nat/bsc_nat
 src/gprs/osmo-sgsn
 src/gprs/osmo-gbproxy
+src/gprs/osmo-gtphub
 src/osmo-bsc_nat/osmo-bsc_nat
 
 #tests
@@ -78,6 +79,7 @@ tests/mgcp/mgcp_transcoding_test
 tests/sgsn/sgsn_test
 tests/subscr/subscr_test
 tests/oap/oap_test
+tests/gtphub/gtphub_test
 
 tests/atconfig
 tests/atlocal
diff --git a/openbsc/configure.ac b/openbsc/configure.ac
index 8b7ce62..098e5b4 100644
--- a/openbsc/configure.ac
+++ b/openbsc/configure.ac
@@ -210,6 +210,7 @@ AC_OUTPUT(
     tests/sgsn/Makefile
     tests/subscr/Makefile
     tests/oap/Makefile
+    tests/gtphub/Makefile
     doc/Makefile
     doc/examples/Makefile
     Makefile)
diff --git a/openbsc/include/openbsc/Makefile.am b/openbsc/include/openbsc/Makefile.am
index 8a074c2..15c38d1 100644
--- a/openbsc/include/openbsc/Makefile.am
+++ b/openbsc/include/openbsc/Makefile.am
@@ -18,6 +18,7 @@ noinst_HEADERS = abis_nm.h abis_rsl.h db.h gsm_04_08.h gsm_data.h \
 		 gprs_gb_parse.h smpp.h meas_feed.h gprs_gsup_messages.h \
 		 gprs_gsup_client.h bsc_msg_filter.h \
 		 oap.h oap_messages.h
+		 gtphub.h
 
 openbsc_HEADERS = gsm_04_08.h meas_rep.h bsc_api.h
 openbscdir = $(includedir)/openbsc
diff --git a/openbsc/include/openbsc/debug.h b/openbsc/include/openbsc/debug.h
index 19d8fc2..189ca47 100644
--- a/openbsc/include/openbsc/debug.h
+++ b/openbsc/include/openbsc/debug.h
@@ -33,6 +33,7 @@ enum {
 	DCTRL,
 	DSMPP,
 	DFILTER,
+	DGTPHUB,
 	Debug_LastEntry,
 };
 
diff --git a/openbsc/include/openbsc/gtphub.h b/openbsc/include/openbsc/gtphub.h
new file mode 100644
index 0000000..ebd4058
--- /dev/null
+++ b/openbsc/include/openbsc/gtphub.h
@@ -0,0 +1,345 @@
+/* GTP Hub Implementation */
+
+/* (C) 2015 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <sys/socket.h>
+
+#include <osmocom/core/select.h>
+#include <osmocom/core/timer.h>
+
+
+/* support */
+
+/* TODO move to osmocom/core/socket.c ? */
+#include <netdb.h> /* for IPPROTO_* etc */
+struct osmo_sockaddr {
+	struct sockaddr_storage a;
+	socklen_t l;
+};
+
+/* TODO move to osmocom/core/socket.c ? */
+/*! \brief Initialize a sockaddr
+ * \param[out] addr  Valid osmo_sockaddr pointer to write result to
+ * \param[in] family  Address Family like AF_INET, AF_INET6, AF_UNSPEC
+ * \param[in] type  Socket type like SOCK_DGRAM, SOCK_STREAM
+ * \param[in] proto  Protocol like IPPROTO_TCP, IPPROTO_UDP
+ * \param[in] host Remote host name or IP address in string form
+ * \param[in] port Remote port number in host byte order
+ * \returns 0 on success, otherwise an error code (from getaddrinfo()).
+ *
+ * Copy the first result from a getaddrinfo() call with the given parameters to
+ * *addr and *addr_len. On error, do not change *addr and return nonzero.
+ */
+int osmo_sockaddr_init(struct osmo_sockaddr *addr,
+		       uint16_t family, uint16_t type, uint8_t proto,
+		       const char *host, uint16_t port);
+
+/* Conveniently pass AF_UNSPEC, SOCK_DGRAM and IPPROTO_UDP to
+ * osmo_sockaddr_init(). */
+static inline int osmo_sockaddr_init_udp(struct osmo_sockaddr *addr,
+					 const char *host, uint16_t port)
+{
+	return osmo_sockaddr_init(addr, AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP, host, port);
+}
+
+/*! \brief convert sockaddr to human readable string.
+ * \param[out] addr_str  Valid pointer to a buffer of length addr_str_len.
+ * \param[in] addr_str_len  Size of buffer addr_str points at.
+ * \param[out] port_str  Valid pointer to a buffer of length port_str_len.
+ * \param[in] port_str_len  Size of buffer port_str points at.
+ * \param[in] addr  Binary representation as returned by osmo_sockaddr_init().
+ * \param[in] flags  flags as passed to getnameinfo().
+ * \returns  0 on success, an error code on error.
+ *
+ * Return the IPv4 or IPv6 address string and the port (a.k.a. service) string
+ * representations of the given struct osmo_sockaddr in two caller provided
+ * char buffers. Flags of (NI_NUMERICHOST | NI_NUMERICSERV) return numeric
+ * address and port. Either one of addr_str or port_str may be NULL, in which
+ * case nothing is returned there.
+ *
+ * See also osmo_sockaddr_to_str() (less flexible, but much more convenient). */
+int osmo_sockaddr_to_strs(char *addr_str, size_t addr_str_len,
+			  char *port_str, size_t port_str_len,
+			  const struct osmo_sockaddr *addr,
+			  int flags);
+
+
+/*! \brief conveniently concatenate the parts returned by osmo_sockaddr_to_strs().
+ * \param[in] addr  Binary representation as returned by osmo_sockaddr_init().
+ * \param[in] buf  A buffer to use for string operations.
+ * \param[in] buf_len  Length of the buffer.
+ * \returns  Address string (in buffer).
+ *
+ * Compose a string of the numeric IP-address and port represented by *addr of
+ * the form "<ip-addr> port <port>". The returned string is valid until the
+ * next invocation of this function.
+ */
+const char *osmo_sockaddr_to_strb(const struct osmo_sockaddr *addr,
+				  char *buf, size_t buf_len);
+
+/*! \brief conveniently return osmo_sockaddr_to_strb() in a static buffer.
+ * \param[in] addr  Binary representation as returned by osmo_sockaddr_init().
+ * \returns  Address string in static buffer.
+ *
+ * See osmo_sockaddr_to_strb().
+ *
+ * Note: only one osmo_sockaddr_to_str() call will work per print/log
+ * statement. For two or more, use osmo_sockaddr_to_strb() with a separate
+ * buffer each.
+ */
+const char *osmo_sockaddr_to_str(const struct osmo_sockaddr *addr);
+
+/*! \brief compare two osmo_sockaddr.
+ * \param[in] a  The first address to compare.
+ * \param[in] b  The other address to compare.
+ * \returns 0 if equal, otherwise -1 or 1.
+ */
+int osmo_sockaddr_cmp(const struct osmo_sockaddr *a, const struct osmo_sockaddr *b);
+
+/*! \brief Overwrite *dst with *src.
+ * Like memcpy(), but copy only the valid bytes. */
+void osmo_sockaddr_copy(struct osmo_sockaddr *dst, const struct osmo_sockaddr *src);
+
+
+/* general */
+
+enum gtphub_port_idx {
+	GTPH_PORT_CTRL = 0,
+	GTPH_PORT_USER = 1,
+	GTPH_PORT_N
+};
+
+extern const char* const gtphub_port_idx_names[GTPH_PORT_N];
+
+
+/* A number map assigns a "random" mapped number to each user provided number.
+ * If the same number is requested multiple times, the same mapped number is
+ * returned.
+ *
+ * Number maps plug into possibly shared pools and expiry queues, for example:
+ *
+ *     mapA -----------+-> pool1           <-+-- mapB
+ *     {10->1, 11->5}  |   {1, 2, 3, ...}    |   {10->2, 11->3}
+ *                     |                     |
+ *                     |                     |
+ *                 /-> \-> expiry1         <-/
+ *                 |       (30 seconds)
+ *                 |
+ *     mapC -------+-----> pool2           <-+-- mapD
+ *     {10->1, 11->3}      {1, 2, 3, ...}    |   {10->2, 11->5}
+ *                                           |
+ *                         expiry2         <-/
+ *                         (60 seconds)
+ *
+ * A map contains mappings ("10->1"). Each map needs a number pool, which can
+ * be shared with other maps. Each new mapping receives a number from the pool,
+ * which is then unavailable to any other map using the same pool.
+ *
+ * A map may point at an expiry queue, in which case all mappings added to it
+ * are also appended to the expiry queue (using a separate llist entry in the
+ * mapping). Any number of maps may submit to the same expiry queue, if they
+ * desire the same expiry timeout. An expiry queue stores the mappings in
+ * chronological order, so that expiry checking is needed only from the start
+ * of the queue; hence only mappings with identical expiry timeout can be added
+ * to the same expiry queue. Upon expiry, a mapping is dropped from the map it
+ * was submitted at. nr_map_expiry_tick() needs to be called regularly for
+ * each expiry queue.
+ *
+ * A nr_mapping can be embedded in a larger struct: each mapping can have a
+ * distinct destructor (del_cb), and each del_cb can figure out the container
+ * struct's address and free that upon expiry or manual deletion. So in expiry
+ * queues (and even maps), mappings of different container types can be mixed.
+ * This can help to drastically reduce the amount of unnecessary visits during
+ * expiry checking, for the case that no expiry is pending. An expiry queue
+ * always knows which mappings to expire next, because they are right at the
+ * start of its list.
+ *
+ * Mapping allocation and a del_cb are provided by the caller. If del_cb is
+ * NULL, no deallocation will be done (allowing statically allocated entries).
+ */
+/* TODO at some point I thought the allocation & del_cb complexity was
+ * needed/helpful, but by now it seems like overkill. Maybe lose that again. */
+
+typedef int nr_t;
+
+/* Generator for unused numbers. So far this counts upwards from zero, but the
+ * implementation may change in the future. Treat this like an opaque struct.
+ * If this becomes random, the tests need to be fixed. */
+struct nr_pool {
+	nr_t last_nr;
+	/* TODO add min, max, for safe wrapping */
+};
+
+struct nr_mapping;
+typedef void (*nr_mapping_del_cb_t)(struct nr_mapping *);
+
+struct nr_mapping {
+	struct llist_head entry;
+	struct llist_head expiry_entry;
+	time_t expiry;
+
+	void *origin;
+	nr_t orig;
+	nr_t repl;
+
+	nr_mapping_del_cb_t del_cb;
+};
+
+struct nr_map_expiry {
+	int expiry_in_seconds;
+	struct llist_head mappings;
+};
+
+struct nr_map {
+	struct nr_pool *pool; /* multiple nr_maps can share a nr_pool. */
+	struct nr_map_expiry *expiry;
+	struct llist_head mappings;
+};
+
+
+void nr_pool_init(struct nr_pool *pool);
+
+/* Return the next unused number from the nr_pool. */
+nr_t nr_pool_next(struct nr_pool *pool);
+
+/* Initialize the nr_mapping to zero/empty values. */
+void nr_mapping_init(struct nr_mapping *mapping);
+
+/* Remove the given mapping from its parent map and expiry queue, and call
+ * mapping->del_cb, if set. */
+void nr_mapping_del(struct nr_mapping *mapping);
+
+/* Initialize an expiry queue exq. */
+void nr_map_expiry_init(struct nr_map_expiry *exq, int expiry_in_seconds);
+
+/* Add a new mapping, or restart the expiry timeout for an already listed mapping. */
+void nr_map_expiry_add(struct nr_map_expiry *exq, struct nr_mapping *mapping, time_t now);
+
+/* Carry out due expiry of mappings. Must be invoked regularly.
+ * 'now' is the current clock count in seconds and must correspond to the clock
+ * count passed to nr_map_add(). A monotonous clock counter should be used. */
+int nr_map_expiry_tick(struct nr_map_expiry *exq, time_t now);
+
+/* Initialize an (already allocated) nr_map, and set the map's number pool.
+ * Multiple nr_map instances may use the same nr_pool. Set the nr_map's expiry
+ * queue to exq, so that all added mappings are automatically expired after the
+ * time configured in exq. exq may be NULL to disable automatic expiry. */
+void nr_map_init(struct nr_map *map, struct nr_pool *pool,
+		 struct nr_map_expiry *exq);
+
+/* Add a new entry to the map. mapping->orig, mapping->origin and
+ * mapping->del_cb must be set before calling this function. The remaining
+ * fields of *mapping will be overwritten. mapping->repl is set to the next
+ * available mapped number from map->pool. 'now' is the current clock count in
+ * seconds; if no map->expiry is used, just pass 0 for 'now'. */
+void nr_map_add(struct nr_map *map, struct nr_mapping *mapping,
+		time_t now);
+
+/* Return a known mapping from nr_orig and the given origin. If nr_orig is
+ * unknown, return NULL. */
+struct nr_mapping *nr_map_get(const struct nr_map *map,
+			      void *origin, nr_t nr_orig);
+
+/* Return a known mapping to nr_repl. If nr_repl is unknown, return NULL. */
+struct nr_mapping *nr_map_get_inv(const struct nr_map *map, nr_t nr_repl);
+
+/* Remove all mappings from map. */
+void nr_map_clear(struct nr_map *map);
+
+/* Return 1 if map has no entries, 0 otherwise. */
+int nr_map_empty(const struct nr_map *map);
+
+
+/* config */
+
+static const int GTPH_SEQ_MAPPING_EXPIRY_SECS = 30; /* TODO is there a spec for this? */
+static const int GTPH_TEI_MAPPING_EXPIRY_MINUTES = 6 * 60; /* TODO is there a spec for this? */
+
+struct gtphub_cfg_addr {
+	const char *addr_str;
+	uint16_t port;
+};
+
+struct gtphub_cfg_bind {
+	struct gtphub_cfg_addr bind;
+};
+
+struct gtphub_cfg {
+	struct gtphub_cfg_bind to_sgsns[GTPH_PORT_N];
+	struct gtphub_cfg_bind to_ggsns[GTPH_PORT_N];
+	struct gtphub_cfg_addr sgsn_proxy[GTPH_PORT_N];
+	struct gtphub_cfg_addr ggsn_proxy[GTPH_PORT_N];
+};
+
+
+/* state */
+
+struct gtphub_peer {
+	struct llist_head entry;
+
+	struct osmo_sockaddr addr;
+	struct nr_map tei_map;
+	struct nr_pool seq_pool;
+	struct nr_map seq_map;
+	unsigned int ref_count; /* references from other peers' seq_maps */
+	struct gtphub_peer *association[GTPH_PORT_N]; /* One points to "this" */
+};
+
+struct gtphub_bind {
+	struct osmo_fd ofd;
+	struct nr_pool tei_pool;
+
+	/* list of struct gtphub_peer */
+	struct llist_head peers;
+};
+
+struct gtphub {
+	struct gtphub_bind to_sgsns[GTPH_PORT_N];
+	struct gtphub_bind to_ggsns[GTPH_PORT_N];
+
+	/* pointers to an entry of to_sgsns[x].peers */
+	struct gtphub_peer *sgsn_proxy[GTPH_PORT_N];
+
+	/* pointers to an entry of to_ggsns[x].peers */
+	struct gtphub_peer *ggsn_proxy[GTPH_PORT_N];
+
+	struct osmo_timer_list gc_timer;
+	struct nr_map_expiry expire_seq_maps;
+	struct nr_map_expiry expire_tei_maps;
+};
+
+struct gtp_packet_desc;
+
+
+/* api */
+
+int gtphub_vty_init(void);
+int gtphub_cfg_read(struct gtphub_cfg *cfg, const char *config_file);
+
+/* Initialize and start gtphub: bind to ports, run expiry timers. */
+int gtphub_start(struct gtphub *hub, struct gtphub_cfg *cfg);
+
+time_t gtphub_now(void);
+
+/* Remove expired items, empty peers, ... */
+void gtphub_gc(struct gtphub *hub, time_t now);
diff --git a/openbsc/include/openbsc/vty.h b/openbsc/include/openbsc/vty.h
index 818a20e..bc30e23 100644
--- a/openbsc/include/openbsc/vty.h
+++ b/openbsc/include/openbsc/vty.h
@@ -36,6 +36,7 @@ enum bsc_vty_node {
 	BSC_NODE,
 	SMPP_NODE,
 	SMPP_ESME_NODE,
+	GTPHUB_NODE,
 };
 
 extern int bsc_vty_is_config_node(struct vty *vty, int node);
diff --git a/openbsc/src/gprs/Makefile.am b/openbsc/src/gprs/Makefile.am
index c8e3696..b2d1774 100644
--- a/openbsc/src/gprs/Makefile.am
+++ b/openbsc/src/gprs/Makefile.am
@@ -11,6 +11,7 @@ noinst_HEADERS = gprs_sndcp.h
 bin_PROGRAMS = osmo-gbproxy
 
 if HAVE_LIBGTP
+bin_PROGRAMS += osmo-gtphub
 if HAVE_LIBCARES
 bin_PROGRAMS += osmo-sgsn
 endif
@@ -33,3 +34,8 @@ osmo_sgsn_LDADD = 	\
 			$(top_builddir)/src/libcommon/libcommon.a \
 			-lgtp $(OSMO_LIBS) $(LIBOSMOABIS_LIBS) $(LIBCARES_LIBS) \
 			$(LIBCRYPTO_LIBS) -lrt
+
+osmo_gtphub_SOURCES =	gtphub_main.c gtphub.c gtphub_sep.c gtphub_vty.c
+osmo_gtphub_LDADD = 	\
+			$(top_builddir)/src/libcommon/libcommon.a \
+			-lgtp $(LIBOSMOCORE_LIBS) $(LIBOSMOVTY_LIBS) -lrt
diff --git a/openbsc/src/gprs/gtphub.c b/openbsc/src/gprs/gtphub.c
new file mode 100644
index 0000000..19246e2
--- /dev/null
+++ b/openbsc/src/gprs/gtphub.c
@@ -0,0 +1,1794 @@
+/* GTP Hub Implementation */
+
+/* (C) 2015 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <string.h>
+#include <errno.h>
+#include <inttypes.h>
+#include <time.h>
+#include <limits.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <gtp.h>
+#include <gtpie.h>
+
+#include <openbsc/gtphub.h>
+#include <openbsc/debug.h>
+
+#include <osmocom/core/utils.h>
+#include <osmocom/core/logging.h>
+#include <osmocom/core/socket.h>
+
+#define GTPHUB_DEBUG 1
+
+static const int GTPH_GC_TICK_SECONDS = 1;
+
+void *osmo_gtphub_ctx;
+
+#define LOGERR(fmt, args...) \
+	LOGP(DGTPHUB, LOGL_ERROR, fmt, ##args)
+
+#define LOG(fmt, args...) \
+	LOGP(DGTPHUB, LOGL_NOTICE, fmt, ##args)
+
+#define ZERO_STRUCT(struct_pointer) memset(struct_pointer, '\0', sizeof(*(struct_pointer)))
+
+/* TODO move this to osmocom/core/select.h ? */
+typedef int (*osmo_fd_cb_t)(struct osmo_fd *fd, unsigned int what);
+
+/* TODO move this to osmocom/core/linuxlist.h ? */
+#define __llist_first(head) (((head)->next == (head)) ? NULL : (head)->next)
+#define llist_first(head, type, entry) llist_entry(__llist_first(head), type, entry)
+
+/* TODO move GTP header stuff to openggsn/gtp/ ? See gtp_decaps*() */
+
+enum gtp_rc {
+	GTP_RC_UNKNOWN = 0,
+	GTP_RC_TINY = 1,    /* no IEs (like ping/pong) */
+	GTP_RC_PDU = 2,     /* a real packet with IEs */
+
+	GTP_RC_TOOSHORT = -1,
+	GTP_RC_UNSUPPORTED_VERSION = -2,
+	GTP_RC_INVALID_IE = -3,
+};
+
+struct gtp_packet_desc {
+	union gtp_packet *data;
+	int data_len;
+	int header_len;
+	int version;
+	int rc; /* enum gtp_rc */
+	unsigned int port_idx;
+	union gtpie_member *ie[GTPIE_SIZE];
+};
+
+/* Validate GTP version 0 data; analogous to validate_gtp1_header(), see there.
+ */
+void validate_gtp0_header(struct gtp_packet_desc *p)
+{
+	const struct gtp0_header *pheader = &(p->data->gtp0.h);
+	p->rc = GTP_RC_UNKNOWN;
+	p->header_len = 0;
+
+	OSMO_ASSERT(p->data_len >= 1);
+	OSMO_ASSERT(p->version == 0);
+
+	if (p->data_len < GTP0_HEADER_SIZE) {
+		LOGERR("GTP0 packet too short: %d\n", p->data_len);
+		p->rc = GTP_RC_TOOSHORT;
+		return;
+	}
+
+	if (p->data_len == GTP0_HEADER_SIZE) {
+		p->rc = GTP_RC_TINY;
+		p->header_len = GTP0_HEADER_SIZE;
+		return;
+	}
+
+	/* Check packet length field versus length of packet */
+	if (p->data_len != (ntoh16(pheader->length) + GTP0_HEADER_SIZE)) {
+		LOGERR("GTP packet length field (%d + %d) does not match"
+		       " actual length (%d)\n",
+		       GTP0_HEADER_SIZE, (int)ntoh16(pheader->length),
+		       p->data_len);
+		p->rc = GTP_RC_TOOSHORT;
+		return;
+	}
+
+	LOG("GTP v0 TID = %" PRIu64 "\n", pheader->tid);
+	p->header_len = GTP0_HEADER_SIZE;
+	p->rc = GTP_RC_PDU;
+}
+
+/* Validate GTP version 1 data, and update p->rc with the result, as well as
+ * p->header_len in case of a valid header. */
+void validate_gtp1_header(struct gtp_packet_desc *p)
+{
+	const struct gtp1_header_long *pheader = &(p->data->gtp1l.h);
+	p->rc = GTP_RC_UNKNOWN;
+	p->header_len = 0;
+
+	OSMO_ASSERT(p->data_len >= 1);
+	OSMO_ASSERT(p->version == 1);
+
+	if ((p->data_len < GTP1_HEADER_SIZE_LONG)
+	    && (p->data_len != GTP1_HEADER_SIZE_SHORT)){
+		LOGERR("GTP packet too short: %d\n", p->data_len);
+		p->rc = GTP_RC_TOOSHORT;
+		return;
+	}
+
+	LOG("|GTPv1\n");
+	LOG("| type = %" PRIu8 " 0x%02" PRIx8 "\n",
+	    pheader->type, pheader->type);
+	LOG("| length = %" PRIu16 " 0x%04" PRIx16 "\n",
+	    ntoh16(pheader->length), ntoh16(pheader->length));
+	LOG("| TEI = %" PRIu32 " 0x%08" PRIx32 "\n",
+	    ntoh32(pheader->tei), ntoh32(pheader->tei));
+	LOG("| seq = %" PRIu16 " 0x%04" PRIx16 "\n",
+	    ntoh16(pheader->seq), ntoh16(pheader->seq));
+	LOG("| npdu = %" PRIu8 " 0x%02" PRIx8 "\n",
+	    pheader->npdu, pheader->npdu);
+	LOG("| next = %" PRIu8 " 0x%02" PRIx8 "\n",
+	    pheader->next, pheader->next);
+
+	if (p->data_len <= GTP1_HEADER_SIZE_LONG) {
+		p->rc = GTP_RC_TINY;
+		p->header_len = GTP1_HEADER_SIZE_SHORT;
+		return;
+	}
+
+	/* Check packet length field versus length of packet */
+	if (p->data_len != (ntoh16(pheader->length) + GTP1_HEADER_SIZE_SHORT)) {
+		LOGERR("GTP packet length field (%d + %d) does not match"
+		       " actual length (%d)\n",
+		       GTP1_HEADER_SIZE_SHORT, (int)ntoh16(pheader->length),
+		       p->data_len);
+		p->rc = GTP_RC_TOOSHORT;
+		return;
+	}
+
+	p->rc = GTP_RC_PDU;
+	p->header_len = GTP1_HEADER_SIZE_LONG;
+}
+
+/* Examine whether p->data of size p->data_len has a valid GTP header. Set
+ * p->version, p->rc and p->header_len. On error, p->rc <= 0 (see enum
+ * gtp_rc). p->data must point at a buffer with p->data_len set. */
+void validate_gtp_header(struct gtp_packet_desc *p)
+{
+	p->rc = GTP_RC_UNKNOWN;
+
+	/* Need at least 1 byte in order to check version */
+	if (p->data_len < 1) {
+		LOGERR("Discarding packet - too small: %d\n", p->data_len);
+		p->rc = GTP_RC_TOOSHORT;
+		return;
+	}
+
+	p->version = p->data->flags >> 5;
+
+	switch (p->version) {
+	case 0:
+		validate_gtp0_header(p);
+		break;
+	case 1:
+		validate_gtp1_header(p);
+		break;
+	default:
+		LOGERR("Unsupported GTP version: %d\n", p->version);
+		p->rc = GTP_RC_UNSUPPORTED_VERSION;
+		break;
+	}
+}
+
+
+/* Return the value of the i'th IMSI IEI by copying to *imsi.
+ * The first IEI is reached by passing i = 0.
+ * imsi must point at allocated space of (at least) 8 bytes.
+ * Return 1 on success, or 0 if not found. */
+static int get_ie_imsi(union gtpie_member *ie[], uint8_t *imsi, int i)
+{
+	return gtpie_gettv0(ie, GTPIE_IMSI, i, imsi, 8) == 0;
+}
+
+/* Analogous to get_ie_imsi(). nsapi must point at a single uint8_t. */
+static int get_ie_nsapi(union gtpie_member *ie[], uint8_t *nsapi, int i)
+{
+	return gtpie_gettv1(ie, GTPIE_NSAPI, i, nsapi) == 0;
+}
+
+static char imsi_digit_to_char(uint8_t nibble)
+{
+	nibble &= 0x0f;
+	if (nibble > 9)
+		return (nibble == 0x0f) ? '\0' : '?';
+	return '0' + nibble;
+}
+
+/* Return a human readable IMSI string, in a static buffer.
+ * imsi must point at 8 octets of IMSI IE encoded IMSI data. */
+static const char *imsi_to_str(uint8_t *imsi)
+{
+	static char str[17];
+	int i;
+
+	for (i = 0; i < 8; i++) {
+		str[2*i] = imsi_digit_to_char(imsi[i]);
+		str[2*i + 1] = imsi_digit_to_char(imsi[i] >> 4);
+	}
+	str[16] = '\0';
+	return str;
+}
+
+/* Validate header, and index information elements. Write decoded packet
+ * information to *res. res->data will point at the given data buffer. On
+ * error, p->rc is set <= 0 (see enum gtp_rc). */
+static void gtp_decode(const uint8_t *data, int data_len,
+		       unsigned int from_port_idx,
+		       struct gtp_packet_desc *res)
+{
+	ZERO_STRUCT(res);
+	res->data = (union gtp_packet*)data;
+	res->data_len = data_len;
+	res->port_idx = from_port_idx;
+
+	validate_gtp_header(res);
+
+	if (res->rc <= 0) {
+		LOGERR("INVALID: dropping GTP packet.\n");
+		return;
+	}
+
+	LOG("Valid GTP header (v%d)\n", res->version);
+
+	if (res->rc != GTP_RC_PDU) {
+		LOG("no IEs in this GTP packet\n");
+		return;
+	}
+
+	if (gtpie_decaps(res->ie, res->version,
+			 (void*)(data + res->header_len),
+			 res->data_len - res->header_len) != 0) {
+		res->rc = GTP_RC_INVALID_IE;
+		return;
+	}
+
+#if GTPHUB_DEBUG
+	int i;
+
+	for (i = 0; i < 10; i++) {
+		uint8_t imsi[8];
+		if (!get_ie_imsi(res->ie, imsi, i))
+			break;
+		LOG("| IMSI %s\n", imsi_to_str(imsi));
+	}
+
+	for (i = 0; i < 10; i++) {
+		uint8_t nsapi;
+		if (!get_ie_nsapi(res->ie, &nsapi, i))
+			break;
+		LOG("| NSAPI %d\n", (int)nsapi);
+	}
+
+	for (i = 0; i < 10; i++) {
+		unsigned int addr_len;
+		struct in_addr addr;
+		if (gtpie_gettlv(res->ie, GTPIE_GSN_ADDR, i, &addr_len, &addr,
+				 sizeof(addr)) != 0)
+			break;
+		LOG("| addr %s\n", inet_ntoa(addr));
+	}
+
+	for (i = 0; i < 10; i++) {
+		uint32_t tei;
+		if (gtpie_gettv4(res->ie, GTPIE_TEI_DI, i, &tei) != 0)
+			break;
+		LOG("| TEI DI (USER) %" PRIu32 " 0x%08" PRIx32 "\n",
+		    tei, tei);
+	}
+
+	for (i = 0; i < 10; i++) {
+		uint32_t tei;
+		if (gtpie_gettv4(res->ie, GTPIE_TEI_C, i, &tei) != 0)
+			break;
+		LOG("| TEI (CTRL) %" PRIu32 " 0x%08" PRIx32 "\n",
+		    tei, tei);
+	}
+#endif
+}
+
+
+/* general */
+
+const char* const gtphub_port_idx_names[GTPH_PORT_N] = {
+	"CTRL",
+	"USER",
+};
+
+time_t gtphub_now(void)
+{
+	struct timespec now_tp;
+	OSMO_ASSERT(clock_gettime(CLOCK_MONOTONIC, &now_tp) >= 0);
+	return now_tp.tv_sec;
+}
+
+
+/* nr_map, nr_pool */
+
+void nr_pool_init(struct nr_pool *pool)
+{
+	*pool = (struct nr_pool){};
+}
+
+nr_t nr_pool_next(struct nr_pool *pool)
+{
+	pool->last_nr ++;
+
+	OSMO_ASSERT(pool->last_nr > 0);
+	/* TODO: gracefully handle running out of TEIs. */
+	/* TODO: random TEIs. */
+
+	return pool->last_nr;
+}
+
+void nr_map_init(struct nr_map *map, struct nr_pool *pool,
+		 struct nr_map_expiry *exq)
+{
+	ZERO_STRUCT(map);
+	map->pool = pool;
+	map->expiry = exq;
+	INIT_LLIST_HEAD(&map->mappings);
+}
+
+void nr_mapping_init(struct nr_mapping *m)
+{
+	ZERO_STRUCT(m);
+	INIT_LLIST_HEAD(&m->entry);
+	INIT_LLIST_HEAD(&m->expiry_entry);
+}
+
+void nr_map_add(struct nr_map *map, struct nr_mapping *mapping, time_t now)
+{
+	/* Generate a mapped number */
+	mapping->repl = nr_pool_next(map->pool);
+
+	/* Add to the tail to always yield a list sorted by expiry, in
+	 * ascending order. */
+	llist_add_tail(&mapping->entry, &map->mappings);
+	if (map->expiry)
+		nr_map_expiry_add(map->expiry, mapping, now);
+}
+
+void nr_map_clear(struct nr_map *map)
+{
+	struct nr_mapping *m;
+	struct nr_mapping *n;
+	llist_for_each_entry_safe(m, n, &map->mappings, entry) {
+		nr_mapping_del(m);
+	}
+}
+
+int nr_map_empty(const struct nr_map *map)
+{
+	return llist_empty(&map->mappings);
+}
+
+struct nr_mapping *nr_map_get(const struct nr_map *map,
+			      void *origin, nr_t nr_orig)
+{
+	struct nr_mapping *mapping;
+	llist_for_each_entry(mapping, &map->mappings, entry) {
+		if ((mapping->origin == origin)
+		    && (mapping->orig == nr_orig))
+			return mapping;
+	}
+	/* Not found. */
+	return NULL;
+}
+
+struct nr_mapping *nr_map_get_inv(const struct nr_map *map, nr_t nr_repl)
+{
+	struct nr_mapping *mapping;
+	llist_for_each_entry(mapping, &map->mappings, entry) {
+		if (mapping->repl == nr_repl) {
+			return mapping;
+		}
+	}
+	/* Not found. */
+	return NULL;
+}
+
+void nr_mapping_del(struct nr_mapping *mapping)
+{
+	OSMO_ASSERT(mapping);
+	llist_del(&mapping->entry);
+	llist_del(&mapping->expiry_entry);
+	if (mapping->del_cb)
+		(mapping->del_cb)(mapping);
+}
+
+void nr_map_expiry_init(struct nr_map_expiry *exq, int expiry_in_seconds)
+{
+	ZERO_STRUCT(exq);
+	exq->expiry_in_seconds = expiry_in_seconds;
+	INIT_LLIST_HEAD(&exq->mappings);
+}
+
+void nr_map_expiry_add(struct nr_map_expiry *exq, struct nr_mapping *mapping,
+		       time_t now)
+{
+	mapping->expiry = now + exq->expiry_in_seconds;
+
+	/* Add/move to the tail to always sort by expiry, ascending. */
+	llist_del(&mapping->expiry_entry);
+	llist_add_tail(&mapping->expiry_entry, &exq->mappings);
+}
+
+int nr_map_expiry_tick(struct nr_map_expiry *exq, time_t now)
+{
+	int expired = 0;
+	struct nr_mapping *m;
+	struct nr_mapping *n;
+	llist_for_each_entry_safe(m, n, &exq->mappings, expiry_entry) {
+		if (m->expiry <= now) {
+			nr_mapping_del(m);
+			expired ++;
+		}
+		else {
+			/* The items are added sorted by expiry. So when we hit
+			 * an unexpired entry, only more unexpired ones will
+			 * follow. */
+			break;
+		}
+	}
+	return expired;
+}
+
+
+/* gtphub */
+
+/* Remove a gtphub_peer from its list and free it. */
+static void gtphub_peer_del(struct gtphub_peer *peer);
+
+/* From the information in the gtp_packet_desc, return the address of a GGSN.
+ * Return -1 on error. */
+static struct gtphub_peer *gtphub_resolve_ggsn(struct gtphub *hub,
+					       struct gtp_packet_desc *p,
+					       unsigned int port_idx);
+
+/* (wrapped by unit test) */
+int gtphub_resolve_ggsn_addr(struct gtphub *hub,
+			     struct osmo_sockaddr *result,
+			     struct gtp_packet_desc *p);
+
+/* comment: see at definition */
+static struct gtphub_peer *gtphub_peer_new(struct gtphub *hub,
+					   struct gtphub_bind bind[],
+					   unsigned int port_idx,
+					   const char *addr_str,
+					   uint16_t port,
+					   const char *other_addr_str,
+					   uint16_t other_port);
+
+static struct gtphub_peer *gtphub_peer_new_from_sockaddr(struct gtphub *hub,
+							 struct gtphub_bind bind[],
+							 unsigned int port_idx,
+							 const struct osmo_sockaddr *addr,
+							 int port_override);
+
+static void gtphub_zero(struct gtphub *hub)
+{
+	ZERO_STRUCT(hub);
+}
+
+static int gtphub_sock_init(struct osmo_fd *ofd,
+			    const struct gtphub_cfg_addr *addr,
+			    osmo_fd_cb_t cb,
+			    void *data,
+			    int ofd_id)
+{
+	if (!addr->addr_str) {
+		LOGERR("Cannot bind: empty address.\n");
+		return -1;
+	}
+	if (!addr->port) {
+		LOGERR("Cannot bind: zero port not permitted.\n");
+		return -1;
+	}
+
+	ofd->when = BSC_FD_READ;
+	ofd->cb = cb;
+	ofd->data = data;
+	ofd->priv_nr = ofd_id;
+
+	int rc;
+	rc = osmo_sock_init_ofd(ofd,
+				AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP,
+				addr->addr_str, addr->port,
+				OSMO_SOCK_F_BIND);
+	if (rc < 1) {
+		LOGERR("Cannot bind to %s port %d (rc %d)\n",
+		       addr->addr_str, (int)addr->port, rc);
+		return -1;
+	}
+
+	return 0;
+}
+
+static void gtphub_gtp_bind_init(struct gtphub_bind *b)
+{
+	ZERO_STRUCT(b);
+
+	nr_pool_init(&b->tei_pool);
+	INIT_LLIST_HEAD(&b->peers);
+}
+
+static int gtphub_gtp_bind_start(struct gtphub_bind *b,
+				 const struct gtphub_cfg_bind *cfg,
+				 osmo_fd_cb_t cb, void *cb_data,
+				 unsigned int ofd_id)
+{
+	if (gtphub_sock_init(&b->ofd, &cfg->bind, cb, cb_data, ofd_id) != 0)
+		return -1;
+	return 0;
+}
+
+/* Recv datagram from from->fd, optionally write sender's address to *from_addr.
+ * Return the number of bytes read, zero on error. */
+static int gtphub_read(const struct osmo_fd *from,
+		       struct osmo_sockaddr *from_addr,
+		       uint8_t *buf, size_t buf_len)
+{
+	/* recvfrom requires the available length to be set in *from_addr_len. */
+	if (from_addr)
+		from_addr->l = sizeof(from_addr->a);
+
+	errno = 0;
+	ssize_t received = recvfrom(from->fd, buf, buf_len, 0,
+				    (struct sockaddr*)&from_addr->a, &from_addr->l);
+	/* TODO use recvmsg and get a MSG_TRUNC flag to make sure the message
+	 * is not truncated. Then maybe reduce buf's size. */
+
+	if (received <= 0) {
+		if (errno != EAGAIN)
+			LOGERR("error: %s\n", strerror(errno));
+		return 0;
+	}
+
+	if (from_addr) {
+		LOG("from %s\n", osmo_sockaddr_to_str(from_addr));
+	}
+
+	if (received <= 0) {
+		LOGERR("error: %s\n", strerror(errno));
+		return 0;
+	}
+
+	LOG("Received %d\n%s\n", (int)received, osmo_hexdump(buf, received));
+	return received;
+}
+
+inline void gtphub_peer_ref_count_inc(struct gtphub_peer *p)
+{
+	OSMO_ASSERT(p->ref_count < UINT_MAX);
+	p->ref_count++;
+}
+
+inline void gtphub_peer_ref_count_dec(struct gtphub_peer *p)
+{
+	OSMO_ASSERT(p->ref_count > 0);
+	p->ref_count--;
+}
+
+inline uint16_t get_seq(struct gtp_packet_desc *p)
+{
+	OSMO_ASSERT(p->version == 1);
+	return ntoh16(p->data->gtp1l.h.seq);
+}
+
+inline void set_seq(struct gtp_packet_desc *p, uint16_t seq)
+{
+	OSMO_ASSERT(p->version == 1);
+	p->data->gtp1l.h.seq = hton16(seq);
+}
+
+inline uint32_t get_tei(struct gtp_packet_desc *p)
+{
+	OSMO_ASSERT(p->version == 1);
+	return ntoh32(p->data->gtp1l.h.tei);
+}
+
+inline void set_tei(struct gtp_packet_desc *p, uint32_t tei)
+{
+	OSMO_ASSERT(p->version == 1);
+	p->data->gtp1l.h.tei = hton32(tei);
+}
+
+static void gtphub_mapping_del_cb(struct nr_mapping *nrm);
+
+static struct nr_mapping *gtphub_mapping_new()
+{
+	struct nr_mapping *nrm;
+	nrm = talloc_zero(osmo_gtphub_ctx, struct nr_mapping);
+	OSMO_ASSERT(nrm);
+
+	nr_mapping_init(nrm);
+	nrm->del_cb = gtphub_mapping_del_cb;
+	return nrm;
+}
+
+static void gtphub_mapping_del_cb(struct nr_mapping *nrm)
+{
+	struct gtphub_peer *from = nrm->origin;
+	OSMO_ASSERT(from);
+	LOG("expired: %d: nr mapping from %s: %d->%d\n",
+	    (int)nrm->expiry,
+	    osmo_sockaddr_to_str(&from->addr),
+	    (int)nrm->orig, (int)nrm->repl);
+
+	gtphub_peer_ref_count_dec(from);
+	talloc_free(nrm);
+}
+
+static struct nr_mapping *gtphub_mapping_have(struct nr_map *map,
+					      struct gtphub_peer *from,
+					      uint16_t orig_nr)
+{
+	struct nr_mapping *nrm;
+
+	nrm = nr_map_get(map, from, orig_nr);
+
+	if (!nrm) {
+		nrm = gtphub_mapping_new();
+		nrm->orig = orig_nr;
+		nrm->origin = from;
+		nr_map_add(map, nrm, gtphub_now());
+		gtphub_peer_ref_count_inc(from);
+		LOG("peer %p: MAP %d --> %d\n", from, (int)(nrm->orig), (int)(nrm->repl));
+	}
+	else {
+		/* restart expiry timeout */
+		nr_map_expiry_add(map->expiry, nrm, gtphub_now());
+	}
+
+	OSMO_ASSERT(nrm);
+	return nrm;
+}
+
+static int gtphub_map_seq(struct gtp_packet_desc *p,
+			  struct gtphub_peer *from_peer, struct gtphub_peer *to_peer)
+{
+	/* Store a mapping in to_peer's map, so when we later receive a GTP
+	 * packet back from to_peer, the seq nr can be unmapped back to its
+	 * origin (from_peer here). */
+	struct nr_mapping *nrm;
+	nrm = gtphub_mapping_have(&to_peer->seq_map, from_peer, get_seq(p));
+
+	/* Change the GTP packet to yield the new, mapped seq nr */
+	set_seq(p, nrm->repl);
+
+	return 0;
+}
+
+static struct gtphub_peer *gtphub_unmap_seq(struct gtp_packet_desc *p,
+					    struct gtphub_peer *responding_peer)
+{
+	OSMO_ASSERT(p->version == 1);
+	struct nr_mapping *nrm = nr_map_get_inv(&responding_peer->seq_map,
+						get_seq(p));
+	if (!nrm)
+		return NULL;
+	LOG("peer %p: UNMAP %d <-- %d\n", nrm->origin, (int)(nrm->orig), (int)(nrm->repl));
+	set_seq(p, nrm->orig);
+	return nrm->origin;
+}
+
+static void gtphub_check_restart_counter(struct gtphub *hub,
+					 struct gtp_packet_desc *p,
+					 struct gtphub_peer *from)
+{
+	/* TODO */
+	/* If the peer is sending a Recovery IE (7.7.11) with a restart counter
+	 * that doesn't match the peer's previously sent restart counter, clear
+	 * that peer and cancel PDP contexts. */
+}
+
+static void gtphub_map_restart_counter(struct gtphub *hub,
+				       struct gtp_packet_desc *p,
+				       struct gtphub_peer *from,
+				       struct gtphub_peer *to)
+{
+	/* TODO */
+}
+
+/* gtphub_map_ie_teis() and gtphub_unmap_header_tei():
+ *
+ * TEI mapping must happen symmetrically. An SGSN contacts gtphub instead of N
+ * GGSNs, and a GGSN replies to gtphub for N SGSNs. From either end, TEIs may
+ * collide: two GGSNs picking the same TEIs, or two SGSNs picking the same
+ * TEIs. Since the opposite side sees the sender address being gtphub's
+ * address, TEIs among the SGSNs, and among the GGSNs, must not overlap. If a
+ * peer sends a TEI already sent before from a peer of the same side, gtphub
+ * replaces it with a TEI not yet seen from that side and remembers the
+ * mapping.
+ *
+ * Consider two SGSNs A and B contacting two GGSNs C and D thru gtphub.
+ *
+ * A: Create PDP Ctx, I have TEI 1.
+ *    --->   gtphub: A has TEI 1, sending 1 for C.
+ *              --->   C: gtphub has TEI 1.
+ *      	<---   C: Reponse to TEI 1: I have TEI 11.
+ *    <---   gtphub: ok, telling A: 11.
+ * A: gtphub's first TEI is 11.                                         (1)
+ *
+ * B: Create PDP Ctx, I have TEIs 1.
+ *    --->   gtphub: 1 already taken for C, sending 2 for B. (map)
+ *              --->   C: gtphub also has 2.
+ *      	<---   C: Reponse to TEI 2: I have TEI 12.
+ *    <---   gtphub: ok, TEI 2 is actually B with TEI 1. (unmap)
+ * B: gtphub's first TEI is 12, as far as I can tell.
+ *
+ * Now the second GGSN comes into play:
+ *
+ * A: Create PDP Ctx, I have TEI 2.
+ *    --->   gtphub: A also has TEI 2, but for D, sending 1.            (2)
+ *              --->   D: gtphub has 1.
+ *      	<---   D: Reponse to TEI 1: I have TEI 11.
+ *    <---   gtphub: from D, 1 is A. 11 already taken by C, sending 13. (3)
+ * A: gtphub also has TEI 13.                                           (4)
+ *
+ * And some messages routed through:
+ *
+ * A: message to TEI 11, see (1).
+ *    --->   gtphub: ok, telling C with TEI 11.
+ *              --->   C: I see, 11 means reply with 1.
+ *      	<---   C: Response to TEI 1
+ *    <---   gtphub: 1 from C is actually for A with TEI 1.
+ * A: ah, my TEI 1, thanks!
+ *
+ * A: message to TEI 13, see (4).
+ *    --->   gtphub: ok, but not 13, D wanted TEI 11 instead, see (3).
+ *              --->   D: I see, 11 means reply with 1.
+ *      	<---   D: Response to TEI 1
+ *    <---   gtphub: 1 from D is actually for A with TEI 2, see (2).
+ * A: ah, my TEI 2, thanks!
+ *
+ * What if a GGSN initiates a request:
+ *
+ *              <---   D: Request to gtphub TEI 1
+ *    <---   gtphub: 1 from D is for A with 2, see (2).
+ * A: my TEI 2 means reply with 13.
+ *    --->   gtphub: 13 was D with 11, see (3).
+ *              --->   D: 11 from gtphub: a reply to my request for TEI 1.
+ *
+ * Note that usually, it's the sequence numbers that route a response back to
+ * the requesting peer. Nevertheless, the TEI mappings must be carried out to
+ * replace the TEIs in the GTP packet that is relayed.
+ *
+ * Also note: the TEI in the GTP header is "reversed" from the TEI in the IEs:
+ * the TEI in the header is used to send something *to* a peer, while the TEI
+ * in e.g. a Create PDP Context Request's IE is for routing messages *back*
+ * later. */
+
+static int gtphub_unmap_header_tei(struct gtphub_peer **to_peer_p,
+				   struct gtphub *hub,
+				   struct gtp_packet_desc *p,
+				   struct gtphub_peer *from_peer)
+{
+	OSMO_ASSERT(p->version == 1);
+
+	struct nr_mapping *nrm;
+	uint32_t tei;
+
+	*to_peer_p = NULL;
+
+	/* If the header's TEI is zero, no PDP context has been established
+	 * yet. If nonzero, a mapping should actually already exist for this
+	 * TEI, since it must have been announced in a PDP context creation. */
+	tei = get_tei(p);
+
+	if (!tei)
+		return 0;
+
+	/* to_peer has previously announced a TEI, which was stored and
+	 * mapped in from_peer's tei_map. */
+	nrm = nr_map_get_inv(&from_peer->tei_map, tei);
+	if (!nrm) {
+		LOGERR("Received unknown TEI %" PRIu32 " from %s\n",
+		       tei, osmo_sockaddr_to_str(&from_peer->addr));
+		return -1;
+	}
+
+	struct gtphub_peer *to_peer = nrm->origin;
+	uint32_t unmapped_tei = nrm->orig;
+	set_tei(p, unmapped_tei);
+
+	char buf[256];
+	LOG("Unmapped TEI coming from %p %s: %d -> %d (to %s)\n",
+	    from_peer, osmo_sockaddr_to_str(&from_peer->addr), tei,
+	    unmapped_tei, osmo_sockaddr_to_strb(&to_peer->addr, buf, sizeof(buf)));
+
+	*to_peer_p = to_peer;
+	return 0;
+}
+
+/* In a packet coming from from_peer, find TEI IE with type number ie_type.  If
+ * it does not exist yet, create a mapping for the TEI in to_peer's map.  A
+ * message coming from to_peer can then be addressed to the (new) mapped TEI,
+ * and will trace back to from_peer and the TEI in this p's IE.
+ *
+ * Also replace the TEI with a mapped TEI in the GTP packet's data buffer. The
+ * buffer can then be sent on to to_peer. */
+static int gtphub_map_tei_ie(struct gtp_packet_desc *p,
+			     uint8_t ie_type, int mandatory,
+			     struct gtphub_peer *from_peer,
+			     struct gtphub_peer *to_peer,
+			     unsigned int port_idx)
+{
+	int ie_idx;
+	uint32_t tei;
+	uint32_t mapped_tei;
+
+	OSMO_ASSERT(from_peer);
+	OSMO_ASSERT(to_peer);
+
+	from_peer = from_peer->association[port_idx];
+	to_peer = to_peer->association[port_idx];
+
+	if (!(from_peer && to_peer)) {
+		LOGERR("Missing peer in %s plane /"
+		       " missing Create PDP Context Request\n",
+		       gtphub_port_idx_names[port_idx]);
+		return -1;
+	}
+
+	ie_idx = gtpie_getie(p->ie, ie_type, 0);
+	if (ie_idx < 0) {
+		if (! mandatory)
+			return 0;
+
+		LOGERR("Create PDP Context Request: Invalid: missing IE %d\n", ie_type);
+		return -1;
+	}
+	tei = ntoh32(p->ie[ie_idx]->tv4.v);
+	/* When to_peer later sends the mapped tei for this tei, we
+	 * want to obtain this tei and from_peer. */
+	struct nr_mapping *nrm;
+	nrm = gtphub_mapping_have(&to_peer->tei_map,
+				  from_peer, tei);
+
+	mapped_tei = nrm->repl;
+	p->ie[ie_idx]->tv4.v = hton32(mapped_tei);
+
+	char buf[256];
+	LOG("Storing new %s TEI in peer %p %s's map: (from %s, TEI %d) -> TEI %d\n",
+	    gtphub_port_idx_names[port_idx],
+	    to_peer,
+	    osmo_sockaddr_to_str(&to_peer->addr),
+	    osmo_sockaddr_to_strb(&from_peer->addr, buf, sizeof(buf)),
+	    tei, mapped_tei);
+
+	return 0;
+}
+
+/* The responding peer does not know that it is going to be the responding peer
+ * yet, but it must already be resolved and initialized. The GTP packet is
+ * coming from requesting_peer.*/
+static int gtphub_handle_create_pdp_req(struct gtphub *hub,
+					struct gtp_packet_desc *p,
+					struct gtphub_peer *requesting_peer,
+					struct gtphub_peer *responding_peer)
+{
+	/* This is a Create PDP Context Request. Expecting this
+	 * to come from the SGSN side. */
+	/* TODO enforce? */
+	int rc;
+	
+	rc = gtphub_map_tei_ie(p, GTPIE_TEI_DI, 1,
+			       requesting_peer, responding_peer,
+			       GTPH_PORT_USER);
+	if (rc < 0)
+		return rc;
+
+	rc = gtphub_map_tei_ie(p, GTPIE_TEI_C, 1,
+			       requesting_peer, responding_peer,
+			       GTPH_PORT_CTRL);
+	return rc;
+}
+
+/* The GTP packet is coming from responding_peer; "responding peer" in the
+ * sense of the Create PDP Context messages. requesting_peer will have been
+ * figured out from sequence number and/or header TEI. */
+static int gtphub_handle_create_pdp_resp(struct gtphub *hub,
+					 struct gtp_packet_desc *p,
+					 struct gtphub_peer *responding_peer,
+					 struct gtphub_peer *requesting_peer)
+{
+	/* This is a Create PDP Context Response. Expecting this
+	 * to come from the GGSN side. */
+	/* TODO enforce? */
+	int rc;
+	
+	rc = gtphub_map_tei_ie(p, GTPIE_TEI_DI, 0,
+			       responding_peer, requesting_peer,
+			       GTPH_PORT_USER);
+	if (rc < 0)
+		return rc;
+
+	rc = gtphub_map_tei_ie(p, GTPIE_TEI_C, 0,
+			       responding_peer, requesting_peer,
+			       GTPH_PORT_CTRL);
+	return rc;
+}
+
+static int gtphub_map_ie_teis(struct gtphub *hub,
+			      struct gtp_packet_desc *p,
+			      struct gtphub_peer *from_peer,
+			      struct gtphub_peer *to_peer)
+{
+	OSMO_ASSERT(p->version == 1);
+	struct gtp1_header_long *h = &p->data->gtp1l.h;
+	uint8_t type = ntoh8(h->type);
+
+	switch (type) {
+	case GTP_CREATE_PDP_REQ:
+		gtphub_handle_create_pdp_req(hub, p, from_peer, to_peer);
+		break;
+
+	case GTP_CREATE_PDP_RSP:
+		gtphub_handle_create_pdp_resp(hub, p, from_peer, to_peer);
+		break;
+
+	default:
+		break;
+	}
+	return 0;
+}
+
+static void gtphub_replace_addresses(struct gtphub *hub,
+				     struct gtp_packet_desc *p,
+				     struct gtphub_peer *from,
+				     struct gtphub_bind *from_bind,
+				     struct gtphub_peer *to,
+				     struct gtphub_bind *to_bind)
+{
+	/* TODO */
+}
+
+static int gtphub_write(struct osmo_fd *to,
+			struct osmo_sockaddr *to_addr,
+			uint8_t *buf, size_t buf_len)
+{
+	errno = 0;
+	ssize_t sent = sendto(to->fd, buf, buf_len, 0,
+			      (struct sockaddr*)&to_addr->a, to_addr->l);
+
+	if (to_addr) {
+		LOG("to %s\n", osmo_sockaddr_to_str(to_addr));
+	}
+
+	if (sent == -1) {
+		LOGERR("error: %s\n", strerror(errno));
+		return -EINVAL;
+	}
+
+	if (sent != buf_len)
+		LOGERR("sent(%d) != data_len(%d)\n", (int)sent, (int)buf_len);
+	else
+		LOG("Sent %d\n%s\n", (int)sent, osmo_hexdump(buf, sent));
+
+	return 0;
+}
+
+int gtphub_from_ggsns_handle_buf(struct gtphub *hub,
+				 unsigned int port_idx,
+				 const struct osmo_sockaddr *from_addr,
+				 uint8_t *buf,
+				 size_t received,
+				 struct osmo_fd **to_ofd,
+				 struct osmo_sockaddr **to_addr);
+
+static struct gtphub_peer *gtphub_peer_find(const struct gtphub_bind *bind,
+					    const struct osmo_sockaddr *addr);
+
+static int from_ggsns_read_cb(struct osmo_fd *from_ggsns_ofd, unsigned int what)
+{
+	unsigned int port_idx = from_ggsns_ofd->priv_nr;
+	OSMO_ASSERT(port_idx < GTPH_PORT_N);
+	LOG("\n\n=== reading from GGSN (%s)\n", gtphub_port_idx_names[port_idx]);
+	if (!(what & BSC_FD_READ))
+		return 0;
+
+	struct gtphub *hub = from_ggsns_ofd->data;
+
+	static uint8_t buf[4096];
+	struct osmo_sockaddr from_addr;
+	struct osmo_sockaddr *to_addr;
+	struct osmo_fd *to_ofd;
+	size_t len;
+	
+	len = gtphub_read(from_ggsns_ofd, &from_addr, buf, sizeof(buf));
+	if (len < 1)
+		return 0;
+
+	len = gtphub_from_ggsns_handle_buf(hub, port_idx, &from_addr, buf, len,
+					   &to_ofd, &to_addr);
+	if (len < 1)
+		return 0;
+
+	return gtphub_write(to_ofd, to_addr, buf, len);
+}
+
+static int gtphub_unmap(struct gtphub *hub,
+			struct gtp_packet_desc *p,
+			struct gtphub_peer *from,
+			struct gtphub_peer *to_proxy,
+			struct gtphub_peer **final_unmapped,
+			struct gtphub_peer **unmapped_from_seq,
+			struct gtphub_peer **unmapped_from_tei)
+{
+	/* Always (try to) unmap sequence and TEI numbers, which need to be
+	 * replaced in the packet. Either way, give precedence to the proxy, if
+	 * configured. */
+
+	struct gtphub_peer *from_seq = NULL;
+	struct gtphub_peer *from_tei = NULL;
+	struct gtphub_peer *unmapped = NULL;
+
+	if (unmapped_from_seq)
+		*unmapped_from_seq = from_seq;
+	if (unmapped_from_tei)
+		*unmapped_from_tei = from_tei;
+	if (final_unmapped)
+		*final_unmapped = unmapped;
+	
+	from_seq = gtphub_unmap_seq(p, from);
+
+	if (gtphub_unmap_header_tei(&from_tei, hub, p, from) < 0)
+		return -1;
+
+	if (from_seq && from_tei && (from_seq != from_tei)) {
+		char b0[256];
+		char b1[256];
+		LOGERR("Seq unmap and TEI unmap yield two different peers. Using seq unmap."
+		       "(from %s %s: seq %d yields %s, tei %u yields %s)\n",
+		       gtphub_port_idx_names[p->port_idx],
+		       osmo_sockaddr_to_str(&from->addr),
+		       (int)get_seq(p),
+		       osmo_sockaddr_to_strb(&from_seq->addr, b0, sizeof(b0)),
+		       (int)get_tei(p),
+		       osmo_sockaddr_to_strb(&from_tei->addr, b1, sizeof(b1))
+		       );
+	}
+	unmapped = (from_seq? from_seq : from_tei);
+
+	if (unmapped && to_proxy && (unmapped != to_proxy)) {
+		char buf[256];
+		LOGERR("Unmap yields a different peer than the configured proxy. Using proxy."
+		       " unmapped: %s  proxy: %s\n",
+		       osmo_sockaddr_to_str(&unmapped->addr),
+		       osmo_sockaddr_to_strb(&to_proxy->addr, buf, sizeof(buf))
+		       );
+	}
+	unmapped = (to_proxy? to_proxy : unmapped);
+
+	if (!unmapped) {
+		/* Return no error, but returned pointers are all NULL. */
+		return 0;
+	}
+
+	LOG("from seq %p; from tei %p; unmapped => %p\n",
+	    from_seq, from_tei, unmapped);
+
+	if (unmapped_from_seq)
+		*unmapped_from_seq = from_seq;
+	if (unmapped_from_tei)
+		*unmapped_from_tei = from_tei;
+	if (final_unmapped)
+		*final_unmapped = unmapped;
+	return 0;
+}
+
+/* Parse buffer as GTP packet, replace elements in-place and return the ofd and
+ * address to forward to. Return the number of bytes to forward, 0 or less on
+ * failure. Return the fd and address to forward to in to_ofd and to_addr. */
+int gtphub_from_ggsns_handle_buf(struct gtphub *hub,
+				 unsigned int port_idx,
+				 const struct osmo_sockaddr *from_addr,
+				 uint8_t *buf,
+				 size_t received,
+				 struct osmo_fd **to_ofd,
+				 struct osmo_sockaddr **to_addr)
+{
+	LOG("<- rx from GGSN %s\n", osmo_sockaddr_to_str(from_addr));
+
+	static struct gtp_packet_desc p;
+	gtp_decode(buf, received, port_idx, &p);
+
+	if (p.rc <= 0)
+		return -1;
+
+	/* If a GGSN proxy is configured, check that it's indeed that proxy
+	 * talking to us. */
+	struct gtphub_peer *ggsn = hub->ggsn_proxy[port_idx];
+	if (ggsn && (osmo_sockaddr_cmp(&ggsn->addr, from_addr) != 0)) {
+		char buf[256];
+		LOGERR("Rejecting: GGSN proxy configured, but GTP packet"
+		       " received on GGSN bind is from another sender:"
+		       " proxy: %s  sender: %s\n", 
+		       osmo_sockaddr_to_str(&ggsn->addr),
+		       osmo_sockaddr_to_strb(from_addr, buf, sizeof(buf)));
+		return -1;
+	}
+
+	if (!ggsn) {
+		/* If any PDP context has been created, we already have an
+		 * entry for this GGSN. If we don't have an entry, the GGSN has
+		 * nothing to tell us about. */
+		ggsn = gtphub_peer_find(&hub->to_ggsns[port_idx], from_addr);
+		LOG("Found peer %p for %s\n", ggsn, osmo_sockaddr_to_str(from_addr));
+	}
+
+	if (!ggsn) {
+		LOGERR("no ggsn\n");
+		return -1;
+	}
+
+	struct gtphub_peer *sgsn_from_seq;
+	struct gtphub_peer *sgsn;
+	if (gtphub_unmap(hub, &p, ggsn,
+			 hub->sgsn_proxy[port_idx],
+			 &sgsn, &sgsn_from_seq, NULL)
+	    != 0) {
+		return -1;
+	}
+
+	if (!sgsn) {
+		LOGERR("No SGSN to send to. Dropping packet.\n");
+		return -1;
+	}
+
+	gtphub_check_restart_counter(hub, &p, ggsn);
+	gtphub_map_restart_counter(hub, &p, ggsn, sgsn);
+	gtphub_replace_addresses(hub, &p,
+				 ggsn, &hub->to_ggsns[port_idx],
+				 sgsn, &hub->to_sgsns[port_idx]);
+
+	/* If the GGSN is replying to an SGSN request, the sequence nr has
+	 * already been unmapped above (sgsn_from_seq != NULL), and we need not
+	 * create a new mapping. */
+	if (!sgsn_from_seq)
+		gtphub_map_seq(&p, ggsn, sgsn);
+
+	/* If IEs announce new TEIs, map those. */
+	if (gtphub_map_ie_teis(hub, &p, ggsn, sgsn) < 0) {
+		LOGERR("Dropping invalid packet\n");
+		return -1;
+	}
+
+	*to_ofd = &hub->to_sgsns[port_idx].ofd;
+	*to_addr = &sgsn->addr;
+
+	return received;
+}
+
+int gtphub_from_sgsns_handle_buf(struct gtphub *hub,
+				 unsigned int port_idx,
+				 const struct osmo_sockaddr *from_addr,
+				 uint8_t *buf,
+				 size_t received,
+				 struct osmo_fd **to_ofd,
+				 struct osmo_sockaddr **to_addr);
+
+static int from_sgsns_read_cb(struct osmo_fd *from_sgsns_ofd, unsigned int what)
+{
+	unsigned int port_idx = from_sgsns_ofd->priv_nr;
+	OSMO_ASSERT(port_idx < GTPH_PORT_N);
+	LOG("\n\n=== reading from SGSN (%s)\n", gtphub_port_idx_names[port_idx]);
+
+	if (!(what & BSC_FD_READ))
+		return 0;
+
+	struct gtphub *hub = from_sgsns_ofd->data;
+
+	static uint8_t buf[4096];
+	struct osmo_sockaddr from_addr;
+	struct osmo_sockaddr *to_addr;
+	struct osmo_fd *to_ofd;
+	size_t len;
+	
+	len = gtphub_read(from_sgsns_ofd, &from_addr, buf, sizeof(buf));
+	if (len < 1)
+		return 0;
+
+	len = gtphub_from_sgsns_handle_buf(hub, port_idx, &from_addr, buf, len,
+					   &to_ofd, &to_addr);
+	if (len < 1)
+		return 0;
+
+	return gtphub_write(to_ofd, to_addr, buf, len);
+}
+
+/* Parse buffer as GTP packet, replace elements in-place and return the ofd and
+ * address to forward to. Return the number of bytes to forward, 0 or less on
+ * failure. Return the fd and address to forward to in to_ofd and to_addr. */
+int gtphub_from_sgsns_handle_buf(struct gtphub *hub,
+				 unsigned int port_idx,
+				 const struct osmo_sockaddr *from_addr,
+				 uint8_t *buf,
+				 size_t received,
+				 struct osmo_fd **to_ofd,
+				 struct osmo_sockaddr **to_addr)
+{
+	LOG("-> rx from SGSN %s\n", osmo_sockaddr_to_str(from_addr));
+
+	static struct gtp_packet_desc p;
+	gtp_decode(buf, received, port_idx, &p);
+
+	if (p.rc <= 0)
+		return -1;
+
+	/* If an SGSN proxy is configured, check that it's indeed that proxy
+	 * talking to us. */
+	struct gtphub_peer *sgsn = hub->sgsn_proxy[port_idx];
+	if (sgsn && (osmo_sockaddr_cmp(&sgsn->addr, from_addr) != 0)) {
+		char buf[256];
+		LOGERR("Rejecting: SGSN proxy configured, but GTP packet"
+		       " received on SGSN bind is from another sender: "
+		       "proxy: %s  sender: %s\n",
+		       osmo_sockaddr_to_str(from_addr),
+		       osmo_sockaddr_to_strb(&sgsn->addr, buf, sizeof(buf)));
+		return -1;
+	}
+
+	if (!sgsn) {
+		/* TODO this is a worthless hack to test things. Instead:
+		   sgsn = gtphub_sgsn_get(hub, ...); */
+		sgsn = llist_first(&hub->to_sgsns[port_idx].peers,
+				   struct gtphub_peer, entry);
+		if (!sgsn) {
+			sgsn = gtphub_peer_new_from_sockaddr(hub,
+							     hub->to_sgsns,
+							     port_idx,
+							     from_addr,
+							     -1);
+			if (!sgsn) {
+				LOG("Packet dropped by preliminary debug code.\n");
+				return -1;
+			}
+			LOG("Created peer %p\n", sgsn);
+		}
+
+		if (osmo_sockaddr_cmp(&sgsn->addr, from_addr) != 0) {
+			char buf[256];
+			LOG("SGSN changed its address from %s to %s\n",
+			    osmo_sockaddr_to_str(&sgsn->addr),
+			    osmo_sockaddr_to_strb(from_addr, buf, sizeof(buf)));
+			memcpy(&sgsn->addr, from_addr, sizeof(sgsn->addr));
+		}
+		LOG("Peer %p = %s\n", sgsn, osmo_sockaddr_to_str(&sgsn->addr));
+	}
+
+	struct gtphub_peer *ggsn_from_seq;
+	struct gtphub_peer *ggsn;
+	if (gtphub_unmap(hub, &p, sgsn,
+			 hub->ggsn_proxy[port_idx],
+			 &ggsn, &ggsn_from_seq, NULL)
+	    != 0) {
+		return -1;
+	}
+
+	/* See what our GGSN guess would be from the packet data per se. */
+	/* TODO maybe not do this always? */
+	struct gtphub_peer *ggsn_from_packet;
+	ggsn_from_packet = gtphub_resolve_ggsn(hub, &p, port_idx);
+
+	if (ggsn_from_packet && ggsn
+	    && (ggsn_from_packet != ggsn)) {
+		char buf[256];
+		LOGERR("GGSN implied from packet does not match unmapped"
+		       " GGSN, using unmapped GGSN:"
+		       " from packet: %s  unmapped: %s\n",
+		       osmo_sockaddr_to_str(&ggsn_from_packet->addr),
+		       osmo_sockaddr_to_strb(&ggsn_from_packet->addr,
+					     buf, sizeof(buf)));
+		/* TODO return -1; ? */
+	}
+
+	if (!ggsn)
+		ggsn = ggsn_from_packet;
+
+	if (!ggsn) {
+		LOGERR("No GGSN to send to. Dropping packet.\n");
+		return -1;
+	}
+
+	gtphub_check_restart_counter(hub, &p, sgsn);
+	gtphub_map_restart_counter(hub, &p, sgsn, ggsn);
+	gtphub_replace_addresses(hub, &p,
+				 sgsn, &hub->to_sgsns[port_idx],
+				 ggsn, &hub->to_ggsns[port_idx]);
+
+	/* If the SGSN is replying to a GGSN request, the sequence nr has
+	 * already been unmapped above (unmap_ggsn != NULL), and we need not
+	 * create a new outgoing sequence map. */
+	if (!ggsn_from_seq)
+		gtphub_map_seq(&p, sgsn, ggsn);
+
+	/* If IEs announce new TEIs, map those. */
+	if (gtphub_map_ie_teis(hub, &p, sgsn, ggsn) < 0) {
+		LOGERR("Dropping invalid packet\n");
+		return -1;
+	}
+
+	*to_ofd = &hub->to_ggsns[port_idx].ofd;
+	*to_addr = &ggsn->addr;
+
+	return received;
+}
+
+static void gtphub_gc_bind(struct gtphub *hub, struct gtphub_bind *b)
+{
+	struct gtphub_peer *p, *n;
+	llist_for_each_entry_safe(p, n, &b->peers, entry) {
+
+		if ((!p->ref_count)
+		    && nr_map_empty(&p->seq_map)) {
+
+			LOG("expired: peer %s\n",
+			    osmo_sockaddr_to_str(&p->addr));
+			gtphub_peer_del(p);
+		}
+	}
+}
+
+void gtphub_gc(struct gtphub *hub, time_t now)
+{
+	int expired;
+	expired = nr_map_expiry_tick(&hub->expire_seq_maps, now);
+	expired += nr_map_expiry_tick(&hub->expire_tei_maps, now);
+
+	/* ... */
+
+	if (expired) {
+		int i;
+		for (i = 0; i < GTPH_PORT_N; i++) {
+			gtphub_gc_bind(hub, &hub->to_sgsns[i]);
+			gtphub_gc_bind(hub, &hub->to_ggsns[i]);
+		}
+	}
+}
+
+static void gtphub_gc_cb(void *data)
+{
+	struct gtphub *hub = data;
+	gtphub_gc(hub, gtphub_now());
+	osmo_timer_schedule(&hub->gc_timer, GTPH_GC_TICK_SECONDS, 0);
+}
+
+static void gtphub_gc_start(struct gtphub *hub)
+{
+	hub->gc_timer.cb = gtphub_gc_cb;
+	hub->gc_timer.data = hub;
+
+	osmo_timer_schedule(&hub->gc_timer, GTPH_GC_TICK_SECONDS, 0);
+}
+
+/* called by unit tests */
+void gtphub_init(struct gtphub *hub)
+{
+	gtphub_zero(hub);
+
+	nr_map_expiry_init(&hub->expire_seq_maps, GTPH_SEQ_MAPPING_EXPIRY_SECS);
+	nr_map_expiry_init(&hub->expire_tei_maps, GTPH_TEI_MAPPING_EXPIRY_MINUTES * 60);
+
+	int port_idx;
+	for (port_idx = 0; port_idx < GTPH_PORT_N; port_idx++) {
+		gtphub_gtp_bind_init(&hub->to_ggsns[port_idx]);
+		gtphub_gtp_bind_init(&hub->to_sgsns[port_idx]);
+	}
+}
+
+int gtphub_start(struct gtphub *hub, struct gtphub_cfg *cfg)
+{
+	int rc;
+
+	gtphub_init(hub);
+
+	int port_idx;
+	for (port_idx = 0; port_idx < GTPH_PORT_N; port_idx++) {
+		rc = gtphub_gtp_bind_start(&hub->to_ggsns[port_idx],
+					   &cfg->to_ggsns[port_idx],
+					   from_ggsns_read_cb, hub, port_idx);
+		if (rc) {
+			LOGERR("Failed to bind for GGSNs (%s)\n",
+			       gtphub_port_idx_names[port_idx]);
+			return rc;
+		}
+
+		rc = gtphub_gtp_bind_start(&hub->to_sgsns[port_idx],
+					   &cfg->to_sgsns[port_idx],
+					   from_sgsns_read_cb, hub, port_idx);
+		if (rc) {
+			LOGERR("Failed to bind for SGSNs (%s)\n",
+			       gtphub_port_idx_names[port_idx]);
+			return rc;
+		}
+	}
+
+	/* SGSN proxy. Trigger only on the control port address. */
+	if (cfg->sgsn_proxy[GTPH_PORT_CTRL].addr_str) {
+		struct gtphub_cfg_addr *addr_c = &cfg->sgsn_proxy[GTPH_PORT_CTRL];
+		struct gtphub_cfg_addr *addr_u = &cfg->sgsn_proxy[GTPH_PORT_USER];
+
+		struct gtphub_peer *sgsn_c;
+		struct gtphub_peer *sgsn_u;
+		sgsn_c = gtphub_peer_new(hub, hub->to_sgsns, GTPH_PORT_CTRL,
+					 addr_c->addr_str, addr_c->port,
+					 addr_u->addr_str, addr_u->port);
+		sgsn_u = sgsn_c->association[GTPH_PORT_USER];
+
+		hub->sgsn_proxy[GTPH_PORT_CTRL] = sgsn_c;
+		hub->sgsn_proxy[GTPH_PORT_USER] = sgsn_u;
+
+		/* This is *the* proxy SGSN. Make sure it is never expired. */
+		gtphub_peer_ref_count_inc(sgsn_c);
+		gtphub_peer_ref_count_inc(sgsn_u);
+
+		LOG("Using SGSN %s proxy %s port %d\n",
+		    gtphub_port_idx_names[GTPH_PORT_CTRL],
+		    addr_c->addr_str,
+		    (int)addr_c->port);
+		LOG("Using SGSN %s proxy %s port %d\n",
+		    gtphub_port_idx_names[GTPH_PORT_USER],
+		    addr_u->addr_str,
+		    (int)addr_u->port);
+	}
+
+	/* GGSN proxy. Trigger only on the control port address. */
+	if (cfg->ggsn_proxy[GTPH_PORT_CTRL].addr_str) {
+		struct gtphub_cfg_addr *addr_c = &cfg->ggsn_proxy[GTPH_PORT_CTRL];
+		struct gtphub_cfg_addr *addr_u = &cfg->ggsn_proxy[GTPH_PORT_USER];
+
+		struct gtphub_peer *ggsn_c;
+		struct gtphub_peer *ggsn_u;
+		ggsn_c = gtphub_peer_new(hub, hub->to_ggsns, GTPH_PORT_CTRL,
+					 addr_c->addr_str, addr_c->port,
+					 addr_u->addr_str, addr_u->port);
+		ggsn_u = ggsn_c->association[GTPH_PORT_USER];
+
+		hub->ggsn_proxy[GTPH_PORT_CTRL] = ggsn_c;
+		hub->ggsn_proxy[GTPH_PORT_USER] = ggsn_u;
+
+		/* This is *the* proxy GGSN. Make sure it is never expired. */
+		gtphub_peer_ref_count_inc(ggsn_c);
+		gtphub_peer_ref_count_inc(ggsn_u);
+
+		LOG("Using GGSN %s proxy %s port %d\n",
+		    gtphub_port_idx_names[GTPH_PORT_CTRL],
+		    addr_c->addr_str,
+		    (int)addr_c->port);
+		LOG("Using GGSN %s proxy %s port %d\n",
+		    gtphub_port_idx_names[GTPH_PORT_USER],
+		    addr_u->addr_str,
+		    (int)addr_u->port);
+	}
+
+	gtphub_gc_start(hub);
+	return 0;
+}
+
+static struct gtphub_peer *_gtphub_peer_new(struct gtphub *hub,
+					    struct gtphub_bind bind[],
+					    unsigned int port_idx,
+					    const char *addr_str,
+					    uint16_t port)
+{
+	struct gtphub_peer *n = talloc_zero(osmo_gtphub_ctx, struct gtphub_peer);
+
+	nr_map_init(&n->tei_map, &bind[port_idx].tei_pool, &hub->expire_tei_maps);
+
+	nr_pool_init(&n->seq_pool);
+	nr_map_init(&n->seq_map, &n->seq_pool, &hub->expire_seq_maps);
+
+	/* TODO use something random to pick the initial sequence nr.
+	   0x6d31 produces the ASCII character sequence 'm1', currently used in
+	   gtphub_nc_test.sh. */
+	n->seq_pool.last_nr = 0x6d31 - 1;
+
+	llist_add(&n->entry, &bind[port_idx].peers);
+
+	if (!port) {
+		port = (port_idx == GTPH_PORT_USER)? GTP1U_PORT : GTP1C_PORT;
+	}
+
+	LOG("New peer: %s %s %d\n", gtphub_port_idx_names[port_idx], addr_str,
+	    (int)port);
+
+	if (osmo_sockaddr_init_udp(&n->addr, addr_str, port) != 0) {
+		LOGERR("Cannot resolve '%s port %d'\n",
+		       addr_str, (int)port);
+		talloc_free(n);
+		return NULL;
+	}
+
+	return n;
+}
+
+/* Create two new gtphub_peer instances added to bind[CTRL]->peers and
+ * bind[USER]->peers.
+ * Initialize:
+ * - point association[port_idx]es to the respective instances,
+ * - resolve the provided addresses,
+ * - set default port numbers for the respective planes, if a given port is 0.
+ * addr_str and port define the peer for the GTP plane indicated by port_idx.
+ * other_addr_str and other_port are used to initialize the peer on the
+ * respective other plane (if port_idx is GTPH_PORT_CTRL, other_addr_str and
+ * other_port are for the User plane). other_addr_str may be NULL, in which
+ * case addr_str is used for both planes. One or both ports may be 0, in which
+ * case the default port for that plane is used.  Return a pointer to the new
+ * instance in the <port_idx> plane, or NULL on error. */
+static struct gtphub_peer *gtphub_peer_new(struct gtphub *hub,
+					   struct gtphub_bind bind[],
+					   unsigned int port_idx,
+					   const char *addr_str,
+					   uint16_t port,
+					   const char *other_addr_str,
+					   uint16_t other_port)
+{
+	if (!other_addr_str)
+		other_addr_str = addr_str;
+
+	const char *addr_str_c;
+	const char *addr_str_u;
+	uint16_t port_c;
+	uint16_t port_u;
+	if (port_idx == GTPH_PORT_CTRL) {
+		addr_str_c = addr_str;
+		addr_str_u = other_addr_str;
+		port_c = port;
+		port_u = other_port;
+	}
+	else {
+		OSMO_ASSERT(port_idx == GTPH_PORT_USER);
+		addr_str_u = addr_str;
+		addr_str_c = other_addr_str;
+		port_u = port;
+		port_c = other_port;
+	}
+
+	struct gtphub_peer *c = _gtphub_peer_new(hub, bind, GTPH_PORT_CTRL,
+						 addr_str_c, port_c);
+	struct gtphub_peer *u = _gtphub_peer_new(hub, bind, GTPH_PORT_USER,
+						 addr_str_u, port_u);
+
+	c->association[GTPH_PORT_CTRL] = u->association[GTPH_PORT_CTRL] = c;
+	c->association[GTPH_PORT_USER] = u->association[GTPH_PORT_USER] = u;
+
+	return c->association[port_idx];
+}
+
+/* port_override: -1: use port from addr; 0: use plane's default port; >0: use
+ * this number as port. */
+static struct gtphub_peer *gtphub_peer_new_from_sockaddr(struct gtphub *hub,
+							 struct gtphub_bind bind[],
+							 unsigned int port_idx,
+							 const struct osmo_sockaddr *addr,
+							 int port_override)
+{
+	char addr_str[256];
+	char port_str[6];
+
+	if (osmo_sockaddr_to_strs(addr_str, sizeof(addr_str),
+				  port_str, sizeof(port_str),
+				  addr,
+				  (NI_NUMERICHOST | NI_NUMERICSERV))
+	    != 0) {
+		return NULL;
+	}
+
+	uint16_t port = port_override < 0? atoi(port_str) : port_override;
+
+	return gtphub_peer_new(hub, bind, port_idx, addr_str, port, NULL, 0);
+}
+
+static void gtphub_peer_del(struct gtphub_peer *peer)
+{
+	nr_map_clear(&peer->seq_map);
+	llist_del(&peer->entry);
+	talloc_free(peer);
+}
+
+static struct gtphub_peer *gtphub_peer_find(const struct gtphub_bind *bind,
+					    const struct osmo_sockaddr *addr)
+{
+	struct gtphub_peer *peer;
+	llist_for_each_entry(peer, &bind->peers, entry) {
+		if (osmo_sockaddr_cmp(addr, &peer->addr) == 0)
+			return peer;
+	}
+	return NULL;
+}
+
+static struct gtphub_peer *gtphub_have_ggsn(struct gtphub *hub,
+					    struct osmo_sockaddr *addr,
+					    unsigned int port_idx)
+{
+	struct gtphub_peer *peer;
+	peer = gtphub_peer_find(&hub->to_ggsns[port_idx], addr);
+	if (peer)
+		return peer;
+
+	/* Not found, create one. */
+	peer = gtphub_peer_new_from_sockaddr(hub, hub->to_ggsns, port_idx, addr, -1);
+	return peer;
+}
+
+static struct gtphub_peer *gtphub_resolve_ggsn(struct gtphub *hub,
+					       struct gtp_packet_desc *p,
+					       unsigned int port_idx)
+{
+	int rc;
+
+	struct osmo_sockaddr addr;
+
+	rc = gtphub_resolve_ggsn_addr(hub, &addr, p);
+	if (rc < 0)
+		return NULL;
+
+	return gtphub_have_ggsn(hub, &addr, port_idx);
+}
+
+
+/* TODO move to osmocom/core/socket.c ? */
+/* The caller is required to call freeaddrinfo(*result), iff zero is returned. */
+/* use this in osmo_sock_init() to remove dup. */
+static int _osmo_getaddrinfo(struct addrinfo **result,
+			     uint16_t family, uint16_t type, uint8_t proto,
+			     const char *host, uint16_t port)
+{
+	struct addrinfo hints;
+	char portbuf[16];
+
+	sprintf(portbuf, "%u", port);
+	memset(&hints, '\0', sizeof(struct addrinfo));
+	hints.ai_family = family;
+	if (type == SOCK_RAW) {
+		/* Workaround for glibc, that returns EAI_SERVICE (-8) if
+		 * SOCK_RAW and IPPROTO_GRE is used.
+		 */
+		hints.ai_socktype = SOCK_DGRAM;
+		hints.ai_protocol = IPPROTO_UDP;
+	} else {
+		hints.ai_socktype = type;
+		hints.ai_protocol = proto;
+	}
+
+	return getaddrinfo(host, portbuf, &hints, result);
+}
+
+/* TODO move to osmocom/core/socket.c ? */
+int osmo_sockaddr_init(struct osmo_sockaddr *addr,
+		       uint16_t family, uint16_t type, uint8_t proto,
+		       const char *host, uint16_t port)
+{
+	struct addrinfo *res;
+	int rc;
+	rc = _osmo_getaddrinfo(&res, family, type, proto, host, port);
+
+	if (rc != 0) {
+		LOGERR("getaddrinfo returned error %d\n", (int)rc);
+		return -EINVAL;
+	}
+
+	OSMO_ASSERT(res->ai_addrlen <= sizeof(addr->a));
+	memcpy(&addr->a, res->ai_addr, res->ai_addrlen);
+	addr->l = res->ai_addrlen;
+	freeaddrinfo(res);
+
+	return 0;
+}
+
+int osmo_sockaddr_to_strs(char *addr_str, size_t addr_str_len,
+			  char *port_str, size_t port_str_len,
+			  const struct osmo_sockaddr *addr,
+			  int flags)
+{
+       int rc;
+
+       if ((addr->l < 1) || (addr->l > sizeof(addr->a))) {
+	       LOGP(DGTPHUB, LOGL_ERROR, "Invalid address size: %d\n", addr->l);
+	       return -1;
+       }
+
+       if (addr->l > sizeof(addr->a)) {
+	       LOGP(DGTPHUB, LOGL_ERROR, "Invalid address: too long: %d\n", addr->l);
+	       return -1;
+       }
+
+       rc = getnameinfo((struct sockaddr*)&addr->a, addr->l,
+			addr_str, addr_str_len,
+			port_str, port_str_len,
+			flags);
+
+       if (rc)
+	       LOGP(DGTPHUB, LOGL_ERROR, "Invalid address: %s: %s\n", gai_strerror(rc),
+		    osmo_hexdump((uint8_t*)&addr->a, addr->l));
+
+       return rc;
+}
+
+const char *osmo_sockaddr_to_strb(const struct osmo_sockaddr *addr,
+				  char *buf, size_t buf_len)
+{
+	const int portbuf_len = 6;
+	OSMO_ASSERT(buf_len > portbuf_len);
+	char *portbuf = buf + buf_len - portbuf_len;
+	buf_len -= portbuf_len;
+	if (osmo_sockaddr_to_strs(buf, buf_len,
+				  portbuf, portbuf_len,
+				  addr,
+				  NI_NUMERICHOST | NI_NUMERICSERV))
+		return NULL;
+
+	char *pos = buf + strnlen(buf, buf_len-1);
+	size_t len = buf_len - (pos - buf);
+
+	snprintf(pos, len, " port %s", portbuf);
+	buf[buf_len-1] = '\0';
+
+	return buf;
+}
+
+const char *osmo_sockaddr_to_str(const struct osmo_sockaddr *addr)
+{
+	static char buf[256];
+	const char *result = osmo_sockaddr_to_strb(addr, buf, sizeof(buf));
+	if (! result)
+		return "(invalid)";
+	return result;
+}
+
+int osmo_sockaddr_cmp(const struct osmo_sockaddr *a, const struct osmo_sockaddr *b)
+{
+	if (a->l != b->l) {
+		/* Lengths are not the same, but determine the order. Will
+		 * anyone ever sort a list by osmo_sockaddr though...? */
+		int cmp = memcmp(&a->a, &b->a, (a->l < b->l)? a->l : b->l);
+		if (cmp == 0) {
+			if (a->l < b->l)
+				return -1;
+			else
+				return 1;
+		}
+		return cmp;
+	}
+	return memcmp(&a->a, &b->a, a->l);
+}
+
+void osmo_sockaddr_copy(struct osmo_sockaddr *dst, const struct osmo_sockaddr *src)
+{
+	OSMO_ASSERT(src->l <= sizeof(dst->a));
+	memcpy(&dst->a, &src->a, src->l);
+	dst->l = src->l;
+}
diff --git a/openbsc/src/gprs/gtphub_main.c b/openbsc/src/gprs/gtphub_main.c
new file mode 100644
index 0000000..84c7969
--- /dev/null
+++ b/openbsc/src/gprs/gtphub_main.c
@@ -0,0 +1,283 @@
+/* GTP Hub main program */
+
+/* (C) 2015 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <unistd.h>
+#include <signal.h>
+#include <string.h>
+#include <errno.h>
+
+#define _GNU_SOURCE
+#include <getopt.h>
+
+#include <osmocom/core/signal.h>
+#include <osmocom/core/application.h>
+#include <osmocom/core/logging.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/core/rate_ctr.h>
+
+#include <osmocom/vty/logging.h>
+#include <osmocom/vty/telnet_interface.h>
+
+#include <openbsc/debug.h>
+#include <openbsc/gtphub.h>
+#include <openbsc/vty.h>
+
+#include "../../bscconfig.h"
+
+#define LOGERR(fmt, args...) \
+	LOGP(DGTPHUB, LOGL_ERROR, fmt, ##args)
+
+#define LOG(fmt, args...) \
+	LOGP(DGTPHUB, LOGL_NOTICE, fmt, ##args)
+
+#ifndef OSMO_VTY_PORT_GTPHUB
+/* should come from libosmocore */
+#define OSMO_VTY_PORT_GTPHUB	4253
+#endif
+
+extern void *osmo_gtphub_ctx;
+
+
+const char *gtphub_copyright =
+	"Copyright (C) 2015 sysmocom s.f.m.c GmbH <info@sysmocom.de>\r\n"
+	"License AGPLv3+: GNU AGPL version 2 or later <http://gnu.org/licenses/agpl-3.0.html>\r\n"
+	"This is free software: you are free to change and redistribute it.\r\n"
+	"There is NO WARRANTY, to the extent permitted by law.\r\n";
+
+static struct log_info_cat gtphub_categories[] = {
+	[DGTPHUB] = {
+		.name = "DGTPHUB",
+		.description = "GTP Hub",
+		.color = "\033[1;33m",
+		.enabled = 1, .loglevel = LOGL_NOTICE,
+	},
+};
+
+int gtphub_log_filter_fn(const struct log_context *ctx,
+			 struct log_target *tar)
+{
+	return 0;
+}
+
+static const struct log_info gtphub_log_info = {
+	.filter_fn = gtphub_log_filter_fn,
+	.cat = gtphub_categories,
+	.num_cat = ARRAY_SIZE(gtphub_categories),
+};
+
+void log_cfg(struct gtphub_cfg *cfg)
+{
+	struct gtphub_cfg_addr *a;
+	a = &cfg->to_sgsns[GTPH_PORT_CTRL].bind;
+	LOG("to-SGSNs bind, Control: %s port %d\n",
+	    a->addr_str, a->port);
+	a = &cfg->to_sgsns[GTPH_PORT_USER].bind;
+	LOG("to-SGSNs bind, User:    %s port %d\n",
+	    a->addr_str, a->port);
+	a = &cfg->to_ggsns[GTPH_PORT_CTRL].bind;
+	LOG("to-GGSNs bind, Control: %s port %d\n",
+	    a->addr_str, a->port);
+	a = &cfg->to_ggsns[GTPH_PORT_USER].bind;
+	LOG("to-GGSNs bind, User:    %s port %d\n",
+	    a->addr_str, a->port);
+}
+
+static void signal_handler(int signal)
+{
+	fprintf(stdout, "signal %u received\n", signal);
+
+	switch (signal) {
+	case SIGINT:
+		osmo_signal_dispatch(SS_L_GLOBAL, S_L_GLOBAL_SHUTDOWN, NULL);
+		sleep(1);
+		exit(0);
+		break;
+	case SIGABRT:
+		/* in case of abort, we want to obtain a talloc report
+		 * and then return to the caller, who will abort the process */
+	case SIGUSR1:
+	case SIGUSR2:
+		talloc_report_full(osmo_gtphub_ctx, stderr);
+		break;
+	default:
+		break;
+	}
+}
+
+extern int bsc_vty_go_parent(struct vty *vty);
+
+static struct vty_app_info vty_info = {
+	.name 		= "OsmoGTPhub",
+	.version	= PACKAGE_VERSION,
+	.go_parent_cb	= bsc_vty_go_parent,
+	.is_config_node	= bsc_vty_is_config_node,
+};
+
+struct cmdline_cfg {
+	const char *config_file;
+	int daemonize;
+};
+
+static void print_help(struct cmdline_cfg *ccfg)
+{
+	printf("gtphub commandline options\n");
+	printf("  -h --help            This text.\n");
+	printf("  -D --daemonize       Fork the process into a background daemon.\n");
+	printf("  -d,--debug <cat>     Enable Debugging for this category.\n");
+	printf("                       Pass '-d list' to get a category listing.\n");
+	printf("  -s --disable-color");
+	printf("  -c --config-file     The config file to use [%s].\n", ccfg->config_file);
+	printf("  -e,--log-level <nr>  Set a global log level.\n");
+}
+
+static void list_categories(void)
+{
+	printf("Avaliable debug categories:\n");
+	int i;
+	for (i = 0; i < gtphub_log_info.num_cat; ++i) {
+		if (!gtphub_log_info.cat[i].name)
+			continue;
+
+		printf("%s\n", gtphub_log_info.cat[i].name);
+	}
+}
+
+static void handle_options(struct cmdline_cfg *ccfg, int argc, char **argv)
+{
+	while (1) {
+		int option_index = 0, c;
+		static struct option long_options[] = {
+			{"help", 0, 0, 'h'},
+			{"debug", 1, 0, 'd'},
+			{"daemonize", 0, 0, 'D'},
+			{"config-file", 1, 0, 'c'},
+			{"disable-color", 0, 0, 's'},
+			{"timestamp", 0, 0, 'T'},
+			{"log-level", 1, 0, 'e'},
+			{NULL, 0, 0, 0}
+		};
+
+		c = getopt_long(argc, argv, "hd:Dc:sTe:",
+				long_options, &option_index);
+		if (c == -1)
+			break;
+
+		switch (c) {
+		case 'h':
+			//print_usage();
+			print_help(ccfg);
+			exit(0);
+		case 's':
+			log_set_use_color(osmo_stderr_target, 0);
+			break;
+		case 'd':
+			if (strcmp("list", optarg) == 0) {
+				list_categories();
+				exit(0);
+			}
+			else
+				log_parse_category_mask(osmo_stderr_target, optarg);
+			break;
+		case 'D':
+			ccfg->daemonize = 1;
+			break;
+		case 'c':
+			ccfg->config_file = optarg;
+			break;
+		case 'T':
+			log_set_print_timestamp(osmo_stderr_target, 1);
+			break;
+		case 'e':
+			log_set_log_level(osmo_stderr_target, atoi(optarg));
+			break;
+		default:
+			/* ignore */
+			break;
+		}
+	}
+}
+
+int main(int argc, char **argv)
+{
+	int rc;
+
+	osmo_gtphub_ctx = talloc_named_const(NULL, 0, "osmo_gtphub");
+
+	signal(SIGINT, &signal_handler);
+	signal(SIGABRT, &signal_handler);
+	signal(SIGUSR1, &signal_handler);
+	signal(SIGUSR2, &signal_handler);
+	osmo_init_ignore_signals();
+
+	osmo_init_logging(&gtphub_log_info);
+
+	vty_info.copyright = gtphub_copyright;
+	vty_init(&vty_info);
+	logging_vty_add_cmds(&gtphub_log_info);
+        gtphub_vty_init();
+
+	rate_ctr_init(osmo_gtphub_ctx);
+	rc = telnet_init(osmo_gtphub_ctx, 0, OSMO_VTY_PORT_GTPHUB);
+	if (rc < 0)
+		exit(1);
+
+	struct cmdline_cfg _ccfg;
+	struct cmdline_cfg *ccfg = &_ccfg;
+	memset(ccfg, '\0', sizeof(*ccfg));
+	ccfg->config_file = "./gtphub.conf";
+
+	struct gtphub_cfg _cfg;
+	struct gtphub_cfg *cfg = &_cfg;
+	memset(cfg, '\0', sizeof(*cfg));
+
+	struct gtphub _hub;
+	struct gtphub *hub = &_hub;
+
+	handle_options(ccfg, argc, argv);
+
+	rc = gtphub_cfg_read(cfg, ccfg->config_file);
+	if (rc < 0) {
+		LOGP(DGTPHUB, LOGL_FATAL, "Cannot parse config file '%s'\n", ccfg->config_file);
+		exit(2);
+	}
+
+	if (gtphub_start(hub, cfg) != 0)
+		return -1;
+
+	log_cfg(cfg);
+
+	if (ccfg->daemonize) {
+		rc = osmo_daemonize();
+		if (rc < 0) {
+			LOGERR("Error during daemonize");
+			exit(1);
+		}
+	}
+
+	while (1) {
+		rc = osmo_select_main(0);
+		if (rc < 0)
+			exit(3);
+	}
+
+	/* not reached */
+	exit(0);
+}
diff --git a/openbsc/src/gprs/gtphub_sep.c b/openbsc/src/gprs/gtphub_sep.c
new file mode 100644
index 0000000..bb31834
--- /dev/null
+++ b/openbsc/src/gprs/gtphub_sep.c
@@ -0,0 +1,26 @@
+/* This file is kept separate so that these functions can be wrapped for
+ * gtphub_test.c. When a function and its callers are in the same compilational
+ * unit, the wrappability may be optimized away. */
+#include <string.h>
+
+#include <openbsc/gtphub.h>
+#include <osmocom/core/utils.h>
+
+#define __llist_first(head) (((head)->next == (head)) ? NULL : (head)->next)
+#define llist_first(head, type, entry) llist_entry(__llist_first(head), type, entry)
+
+int gtphub_resolve_ggsn_addr(struct gtphub *hub,
+			     struct osmo_sockaddr *result,
+			     struct gtp_packet_desc *p)
+{
+	/* TODO  This is just hardcodedly returning the first known address.
+	 * Should resolve from actual subscriber data. */
+	struct gtphub_peer *ggsn = llist_first(&hub->to_ggsns[GTPH_PORT_CTRL].peers,
+					       struct gtphub_peer, entry);
+	if (!ggsn)
+		return -1;
+
+	memcpy(result, &ggsn->addr, sizeof(struct osmo_sockaddr));
+	return 0;
+}
+
diff --git a/openbsc/src/gprs/gtphub_vty.c b/openbsc/src/gprs/gtphub_vty.c
new file mode 100644
index 0000000..2227d48
--- /dev/null
+++ b/openbsc/src/gprs/gtphub_vty.c
@@ -0,0 +1,258 @@
+/* (C) 2015 by sysmocom s.f.m.c. GmbH
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <string.h>
+
+#include <osmocom/core/talloc.h>
+#include <osmocom/vty/command.h>
+
+#include <openbsc/vty.h>
+#include <openbsc/gtphub.h>
+
+static struct gtphub_cfg *g_cfg = 0;
+
+static struct cmd_node gtphub_node = {
+	GTPHUB_NODE,
+	"%s(config-gtphub)# ",
+	1,
+};
+
+#define GTPH_DEFAULT_CONTROL_PORT 2123
+#define GTPH_DEFAULT_USER_PORT 2152
+
+static void write_addrs(struct vty *vty, const char *name,
+			struct gtphub_cfg_addr *c, struct gtphub_cfg_addr *u)
+{
+	if ((c->port == GTPH_DEFAULT_CONTROL_PORT)
+	    && (u->port == GTPH_DEFAULT_USER_PORT)
+	    && (strcmp(c->addr_str, u->addr_str) == 0)) {
+		/* Default port numbers and same IP address: write "short"
+		 * variant. */
+		vty_out(vty, " %s %s%s",
+			name,
+			c->addr_str,
+			VTY_NEWLINE);
+		return;
+	}
+
+	vty_out(vty, " %s ctrl %s %d user %s %d%s",
+		name,
+		c->addr_str, (int)c->port,
+		u->addr_str, (int)u->port,
+		VTY_NEWLINE);
+}
+
+static int config_write_gtphub(struct vty *vty)
+{
+	vty_out(vty, "gtphub%s", VTY_NEWLINE);
+
+	write_addrs(vty, "bind-to-sgsns",
+		    &g_cfg->to_sgsns[GTPH_PORT_CTRL].bind,
+		    &g_cfg->to_sgsns[GTPH_PORT_USER].bind);
+
+	write_addrs(vty, "bind-to-ggsns",
+		    &g_cfg->to_ggsns[GTPH_PORT_CTRL].bind,
+		    &g_cfg->to_ggsns[GTPH_PORT_USER].bind);
+
+	if (g_cfg->ggsn_proxy[GTPH_PORT_CTRL].addr_str) {
+		write_addrs(vty, "ggsn-proxy",
+			    &g_cfg->ggsn_proxy[GTPH_PORT_CTRL],
+			    &g_cfg->ggsn_proxy[GTPH_PORT_USER]);
+	}
+
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gtphub, cfg_gtphub_cmd,
+      "gtphub",
+      "Configure the GTP hub")
+{
+	vty->node = GTPHUB_NODE;
+	return CMD_SUCCESS;
+}
+
+#define BIND_ARGS  "ctrl ADDR <0-65535> user ADDR <0-65535>"
+#define BIND_DOCS  \
+	"Set GTP-C bind\n" \
+	"GTP-C local IP address (v4 or v6)\n" \
+	"GTP-C local port\n" \
+	"Set GTP-U bind\n" \
+	"GTP-U local IP address (v4 or v6)\n" \
+	"GTP-U local port\n"
+
+
+DEFUN(cfg_gtphub_bind_to_sgsns_short, cfg_gtphub_bind_to_sgsns_short_cmd,
+	"bind-to-sgsns ADDR",
+	"GTP Hub Parameters\n"
+	"Set the local bind address to listen for SGSNs, for both GTP-C and GTP-U\n"
+	"Local IP address (v4 or v6)\n"
+	)
+{
+	int i;
+	for (i = 0; i < GTPH_PORT_N; i++)
+		g_cfg->to_sgsns[i].bind.addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->to_sgsns[GTPH_PORT_CTRL].bind.port = GTPH_DEFAULT_CONTROL_PORT;
+	g_cfg->to_sgsns[GTPH_PORT_USER].bind.port = GTPH_DEFAULT_USER_PORT;
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gtphub_bind_to_ggsns_short, cfg_gtphub_bind_to_ggsns_short_cmd,
+	"bind-to-ggsns ADDR",
+	"GTP Hub Parameters\n"
+	"Set the local bind address to listen for GGSNs, for both GTP-C and GTP-U\n"
+	"Local IP address (v4 or v6)\n"
+	)
+{
+	int i;
+	for (i = 0; i < GTPH_PORT_N; i++)
+		g_cfg->to_ggsns[i].bind.addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->to_ggsns[GTPH_PORT_CTRL].bind.port = GTPH_DEFAULT_CONTROL_PORT;
+	g_cfg->to_ggsns[GTPH_PORT_USER].bind.port = GTPH_DEFAULT_USER_PORT;
+	return CMD_SUCCESS;
+}
+
+
+static int handle_binds(struct gtphub_cfg_bind *b, const char **argv)
+{
+	b[GTPH_PORT_CTRL].bind.addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	b[GTPH_PORT_CTRL].bind.port = atoi(argv[1]);
+	b[GTPH_PORT_USER].bind.addr_str = talloc_strdup(tall_vty_ctx, argv[2]);
+	b[GTPH_PORT_USER].bind.port = atoi(argv[3]);
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gtphub_bind_to_sgsns, cfg_gtphub_bind_to_sgsns_cmd,
+	"bind-to-sgsns " BIND_ARGS,
+	"GTP Hub Parameters\n"
+	"Set the local bind addresses and ports to listen for SGSNs\n"
+	BIND_DOCS
+	)
+{
+	return handle_binds(g_cfg->to_sgsns, argv);
+}
+
+DEFUN(cfg_gtphub_bind_to_ggsns, cfg_gtphub_bind_to_ggsns_cmd,
+	"bind-to-ggsns " BIND_ARGS,
+	"GTP Hub Parameters\n"
+	"Set the local bind addresses and ports to listen for GGSNs\n"
+	BIND_DOCS
+	)
+{
+	return handle_binds(g_cfg->to_ggsns, argv);
+}
+
+DEFUN(cfg_gtphub_ggsn_proxy_short, cfg_gtphub_ggsn_proxy_short_cmd,
+	"ggsn-proxy ADDR",
+	"GTP Hub Parameters\n"
+	"Redirect all GGSN bound traffic to default ports on this address (another gtphub)\n"
+	"Remote IP address (v4 or v6)\n"
+	)
+{
+	g_cfg->ggsn_proxy[GTPH_PORT_CTRL].addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->ggsn_proxy[GTPH_PORT_CTRL].port = GTPH_DEFAULT_CONTROL_PORT;
+	g_cfg->ggsn_proxy[GTPH_PORT_USER].addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->ggsn_proxy[GTPH_PORT_USER].port = GTPH_DEFAULT_USER_PORT;
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gtphub_ggsn_proxy, cfg_gtphub_ggsn_proxy_cmd,
+	"ggsn-proxy " BIND_ARGS,
+	"GTP Hub Parameters\n"
+	"Redirect all GGSN bound traffic to these addresses and ports (another gtphub)\n"
+	BIND_DOCS
+	)
+{
+	g_cfg->ggsn_proxy[GTPH_PORT_CTRL].addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->ggsn_proxy[GTPH_PORT_CTRL].port = atoi(argv[1]);
+	g_cfg->ggsn_proxy[GTPH_PORT_USER].addr_str = talloc_strdup(tall_vty_ctx, argv[2]);
+	g_cfg->ggsn_proxy[GTPH_PORT_USER].port = atoi(argv[3]);
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gtphub_sgsn_proxy_short, cfg_gtphub_sgsn_proxy_short_cmd,
+	"sgsn-proxy ADDR",
+	"GTP Hub Parameters\n"
+	"Redirect all SGSN bound traffic to default ports on this address (another gtphub)\n"
+	"Remote IP address (v4 or v6)\n"
+	)
+{
+	g_cfg->sgsn_proxy[GTPH_PORT_CTRL].addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->sgsn_proxy[GTPH_PORT_CTRL].port = GTPH_DEFAULT_CONTROL_PORT;
+	g_cfg->sgsn_proxy[GTPH_PORT_USER].addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->sgsn_proxy[GTPH_PORT_USER].port = GTPH_DEFAULT_USER_PORT;
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_gtphub_sgsn_proxy, cfg_gtphub_sgsn_proxy_cmd,
+	"sgsn-proxy " BIND_ARGS,
+	"GTP Hub Parameters\n"
+	"Redirect all SGSN bound traffic to these addresses and ports (another gtphub)\n"
+	BIND_DOCS
+	)
+{
+	g_cfg->sgsn_proxy[GTPH_PORT_CTRL].addr_str = talloc_strdup(tall_vty_ctx, argv[0]);
+	g_cfg->sgsn_proxy[GTPH_PORT_CTRL].port = atoi(argv[1]);
+	g_cfg->sgsn_proxy[GTPH_PORT_USER].addr_str = talloc_strdup(tall_vty_ctx, argv[2]);
+	g_cfg->sgsn_proxy[GTPH_PORT_USER].port = atoi(argv[3]);
+	return CMD_SUCCESS;
+}
+
+DEFUN(show_gtphub, show_gtphub_cmd, "show gtphub",
+      SHOW_STR "Display information about the GTP hub")
+{
+	vty_out(vty, "gtphub has nothing to say yet%s", VTY_NEWLINE);
+	return CMD_SUCCESS;
+}
+
+
+int gtphub_vty_init(void)
+{
+	install_element_ve(&show_gtphub_cmd);
+
+	install_element(CONFIG_NODE, &cfg_gtphub_cmd);
+	install_node(&gtphub_node, config_write_gtphub);
+	vty_install_default(GTPHUB_NODE);
+
+	install_element(GTPHUB_NODE, &cfg_gtphub_bind_to_sgsns_short_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_bind_to_sgsns_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_bind_to_ggsns_short_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_bind_to_ggsns_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_ggsn_proxy_short_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_ggsn_proxy_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_sgsn_proxy_short_cmd);
+	install_element(GTPHUB_NODE, &cfg_gtphub_sgsn_proxy_cmd);
+
+	return 0;
+}
+
+int gtphub_cfg_read(struct gtphub_cfg *cfg, const char *config_file)
+{
+	int rc;
+
+	g_cfg = cfg;
+
+	rc = vty_read_config_file(config_file, NULL);
+	if (rc < 0) {
+		fprintf(stderr, "Failed to parse the config file: '%s'\n", config_file);
+		return rc;
+	}
+
+	return 0;
+}
diff --git a/openbsc/tests/Makefile.am b/openbsc/tests/Makefile.am
index 1b557d4..aacfe0b 100644
--- a/openbsc/tests/Makefile.am
+++ b/openbsc/tests/Makefile.am
@@ -1,4 +1,4 @@
-SUBDIRS = gsm0408 db channel mgcp gprs abis gbproxy trau subscr oap
+SUBDIRS = gsm0408 db channel mgcp gprs abis gbproxy trau subscr oap gtphub
 
 if BUILD_NAT
 SUBDIRS += bsc-nat bsc-nat-trie
diff --git a/openbsc/tests/gtphub/Makefile.am b/openbsc/tests/gtphub/Makefile.am
new file mode 100644
index 0000000..ecc6d62
--- /dev/null
+++ b/openbsc/tests/gtphub/Makefile.am
@@ -0,0 +1,20 @@
+AM_CPPFLAGS = $(all_includes) -I$(top_srcdir)/include
+AM_CFLAGS=-Wall -ggdb3 $(LIBOSMOCORE_CFLAGS)
+
+EXTRA_DIST = \
+	gtphub_test.ok \
+	gtphub_nc_test.sh \
+	gtphub_nc_test.ok \
+	hex2bin.py
+
+noinst_PROGRAMS = gtphub_test
+
+gtphub_test_SOURCES = gtphub_test.c
+gtphub_test_LDFLAGS = \
+	-Wl,--wrap=gtphub_resolve_ggsn_addr
+
+gtphub_test_LDADD = \
+	$(top_builddir)/src/gprs/gtphub.o \
+	$(LIBOSMOCORE_LIBS) \
+	-lgtp -lrt
+
diff --git a/openbsc/tests/gtphub/gtphub_nc_test.gtphub.conf b/openbsc/tests/gtphub/gtphub_nc_test.gtphub.conf
new file mode 100644
index 0000000..17cc756
--- /dev/null
+++ b/openbsc/tests/gtphub/gtphub_nc_test.gtphub.conf
@@ -0,0 +1,5 @@
+gtphub
+ bind-to-sgsns ctrl 127.0.0.1 21231 user 127.0.0.1 21521
+ bind-to-ggsns ctrl 127.0.0.1 21232 user 127.0.0.1 21522
+ ggsn-proxy 127.0.0.1
+end
diff --git a/openbsc/tests/gtphub/gtphub_nc_test.ok b/openbsc/tests/gtphub/gtphub_nc_test.ok
new file mode 100644
index 0000000..6a6db53
--- /dev/null
+++ b/openbsc/tests/gtphub/gtphub_nc_test.ok
@@ -0,0 +1,7 @@
+--- recv_server:
+32 01 00 04 00 00 00 00 6d 31 00 00
+OK
+--- recv_client:
+32 02 00 06 00 00 00 00 7c 00 00 00 0e 01
+OK
+done
diff --git a/openbsc/tests/gtphub/gtphub_nc_test.sh b/openbsc/tests/gtphub/gtphub_nc_test.sh
new file mode 100755
index 0000000..febb5a7
--- /dev/null
+++ b/openbsc/tests/gtphub/gtphub_nc_test.sh
@@ -0,0 +1,85 @@
+#!/usr/bin/env bash
+# gtphub_nc_test.sh
+
+# TODO does this work with all relevant netcat implementations?
+# TODO skip if netcat not found?
+# TODO use only 127.0.0.1 once gtphub is configurable.
+
+dump() {
+  # echo result to strip trailing space
+  echo $(hexdump -v -e '/1 "%02x "' $@)
+}
+
+sendhex() {
+  hex="$1"
+  from_port="$2"
+  to_port="$3"
+  echo "$hex" | ./hex2bin.py | nc --send-only -u -s 127.0.0.1 -p "$from_port" 127.0.0.1 "$to_port"
+}
+
+gtphub_bin="./osmo-gtphub"
+if [ ! -x "$gtphub_bin" ]; then
+	echo "executable not found: $gtphub_bin"
+	exit 1;
+fi
+
+#  client              osmo-gtphub                            gtp server
+#  127.0.0.1:9876 <--> 127.0.0.1:21231 | 127.0.0.1:21232 <--> 127.0.0.1 2123
+#  (netcat)            ($gtphub_bin)                          (netcat)
+
+# start gtphub relay
+"$gtphub_bin" -c gtphub.conf &
+sleep 0.1
+
+# log what reaches client and server
+nc --recv-only -u -l -p 9876 -s 127.0.0.1 > recv_client &
+nc --recv-only -u -l -p 2123 -s 127.0.0.1 > recv_server &
+sleep .1
+
+# send test messages, both ways...
+# When sending the ping, the sequence number gets mapped (7c00 -> 6d31).
+# In the pong, the mapped sequence nr is sent and gets mapped backwards.
+gtp_ping_seq1="32 01 00 04 00 00 00 00 7c 00 00 00"
+gtp_ping_seq2="32 01 00 04 00 00 00 00 6d 31 00 00"
+gtp_pong_seq2="32 02 00 06 00 00 00 00 6d 31 00 00 0e 01"
+gtp_pong_seq1="32 02 00 06 00 00 00 00 7c 00 00 00 0e 01"
+
+sendhex "$gtp_ping_seq1" 9876 21231
+
+# server sends reply with the mapped sequence nr., but wrong sender in terms of
+# the configured GGSN proxy address.
+sendhex "$gtp_pong_seq2" 7777 21232
+
+# server sends reply with the mapped sequence nr., correct sender
+sendhex "$gtp_pong_seq2" 2123 21232
+
+sleep .1
+kill %1 %2 %3
+
+# log what has reached the server and client ends, matched against
+# gtphub_nc_test.ok
+retval=0
+rx_srv="$(dump recv_server)"
+echo "--- recv_server:"
+echo "$rx_srv"
+
+if [ "$rx_srv" = "$gtp_ping_seq2" ]; then
+	echo "OK"
+else
+	echo "*** FAILURE"
+	retval=1
+fi
+
+rx_clt="$(dump recv_client)"
+echo "--- recv_client:"
+echo "$rx_clt"
+
+if [ "$rx_clt" = "$gtp_pong_seq1" ]; then
+	echo "OK"
+else
+	echo "*** FAILURE"
+	retval=2
+fi
+
+echo "done"
+exit "$retval"
diff --git a/openbsc/tests/gtphub/gtphub_test.c b/openbsc/tests/gtphub/gtphub_test.c
new file mode 100644
index 0000000..5a5c4d1
--- /dev/null
+++ b/openbsc/tests/gtphub/gtphub_test.c
@@ -0,0 +1,675 @@
+/* Test the GTP hub */
+
+/* (C) 2015 by sysmocom s.f.m.c. GmbH
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr <nhofmeyr@sysmcom.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <limits.h>
+#include <unistd.h>
+
+#include <osmocom/core/utils.h>
+#include <osmocom/core/msgb.h>
+#include <osmocom/core/application.h>
+
+#include <openbsc/debug.h>
+
+#include <openbsc/gtphub.h>
+#include <gtp.h>
+#include <gtpie.h>
+
+#define EXPIRE_ALL (gtphub_now() + (60 * GTPH_TEI_MAPPING_EXPIRY_MINUTES) + 1)
+
+/* Make non-public API accessible */
+
+void gtphub_init(struct gtphub *hub);
+
+int gtphub_from_sgsns_handle_buf(struct gtphub *hub,
+				 unsigned int port_idx,
+				 const struct osmo_sockaddr *from_addr,
+				 uint8_t *buf,
+				 size_t received,
+				 struct osmo_fd **to_ofd,
+				 struct osmo_sockaddr **to_addr);
+
+int gtphub_from_ggsns_handle_buf(struct gtphub *hub,
+				 unsigned int port_idx,
+				 const struct osmo_sockaddr *from_addr,
+				 uint8_t *buf,
+				 size_t received,
+				 struct osmo_fd **to_ofd,
+				 struct osmo_sockaddr **to_addr);
+
+void *osmo_gtphub_ctx;
+
+/* TODO copied from libosmo-abis/src/subchan_demux.c, remove dup */
+static int llist_len(struct llist_head *head)
+{
+	struct llist_head *entry;
+	int i = 0;
+
+	llist_for_each(entry, head)
+		i++;
+
+	return i;
+}
+
+static void nr_mapping_free(struct nr_mapping *m)
+{
+	talloc_free(m);
+}
+
+static struct nr_mapping *nr_mapping_alloc(void)
+{
+	struct nr_mapping *m;
+	m = talloc(osmo_gtphub_ctx, struct nr_mapping);
+	nr_mapping_init(m);
+	m->del_cb = nr_mapping_free;
+	return m;
+}
+
+static struct nr_mapping *nr_map_have(struct nr_map *map, void *origin, nr_t orig, time_t now)
+{
+	struct nr_mapping *mapping;
+
+	mapping = nr_map_get(map, origin, orig);
+	if (!mapping) {
+		mapping = nr_mapping_alloc();
+		mapping->origin = origin;
+		mapping->orig = orig;
+		nr_map_add(map, mapping, now);
+	}
+
+	return mapping;
+}
+
+static nr_t nr_map_verify(const struct nr_map *map, void *origin, nr_t orig, nr_t expect_repl)
+{
+	struct nr_mapping *m;
+	m = nr_map_get(map, origin, orig);
+
+	if (!m) {
+		printf("mapping not found for %p %d\n", origin, orig);
+		return 0;
+	}
+
+	if (m->repl != expect_repl) {
+		printf("mapping found, but nr mismatches: expect %d, got %d\n",
+		       (int)expect_repl, (int)m->repl);
+		return 0;
+	}
+
+	return 1;
+}
+
+static int nr_map_verify_inv(const struct nr_map *map, nr_t repl,
+			     void *expect_origin, nr_t expect_orig)
+{
+	struct nr_mapping *m;
+	m = nr_map_get_inv(map, repl);
+	if (!m) {
+		printf("mapping not found for %d\n", (int)repl);
+		return 0;
+	}
+
+	if (m->origin != expect_origin) {
+		printf("mapping found, but origin mismatches: expect %p, got %p\n",
+		       expect_origin, m->origin);
+		return 0;
+	}
+
+	if (m->orig != expect_orig) {
+		printf("mapping found, but nr mismatches: expect %d, got %d\n",
+		       (int)expect_orig, (int)m->orig);
+		return 0;
+	}
+
+	return 1;
+}
+
+
+static void test_nr_map_basic(void)
+{
+	struct nr_pool _pool;
+	struct nr_pool *pool = &_pool;
+	struct nr_map _map;
+	struct nr_map *map = &_map;
+
+	nr_pool_init(pool);
+	nr_map_init(map, pool, NULL);
+
+	OSMO_ASSERT(llist_empty(&map->mappings));
+
+#define TEST_N_HALF 100
+#define TEST_N (2*TEST_N_HALF)
+#define TEST_I 123
+	uint32_t i, check_i;
+	uint32_t m[TEST_N];
+	struct nr_mapping *mapping;
+
+	/* create half of TEST_N mappings from one origin */
+	void *origin1 = (void*)0x1234;
+	for (i = 0; i < TEST_N_HALF; i++) {
+		nr_t orig = TEST_I + i;
+		mapping = nr_map_have(map, origin1, orig, 0);
+		m[i] = mapping->repl;
+		OSMO_ASSERT(m[i] != 0);
+		OSMO_ASSERT(llist_len(&map->mappings) == (i+1));
+		for (check_i = 0; check_i < i; check_i++)
+			OSMO_ASSERT(m[check_i] != m[i]);
+	}
+	OSMO_ASSERT(llist_len(&map->mappings) == TEST_N_HALF);
+
+	/* create another TEST_N mappings with the same original numbers, but
+	 * from a different origin */
+	void *origin2 = (void*)0x5678;
+	for (i = 0; i < TEST_N_HALF; i++) {
+		int i2 = TEST_N_HALF + i;
+		nr_t orig = TEST_I + i;
+		mapping = nr_map_have(map, origin2, orig, 0);
+		m[i2] = mapping->repl;
+		OSMO_ASSERT(m[i2] != 0);
+		OSMO_ASSERT(llist_len(&map->mappings) == (i2+1));
+		for (check_i = 0; check_i < i2; check_i++)
+			OSMO_ASSERT(m[check_i] != m[i2]);
+	}
+	OSMO_ASSERT(llist_len(&map->mappings) == TEST_N);
+
+	/* verify mappings */
+	for (i = 0; i < TEST_N_HALF; i++) {
+		nr_t orig = TEST_I + i;
+		{
+			OSMO_ASSERT(nr_map_verify(map, origin1, orig, m[i]));
+			OSMO_ASSERT(nr_map_verify_inv(map, m[i], origin1, orig));
+		}
+		{
+			int i2 = TEST_N_HALF + i;
+			OSMO_ASSERT(nr_map_verify(map, origin2, orig, m[i2]));
+			OSMO_ASSERT(nr_map_verify_inv(map, m[i2], origin2, orig));
+		}
+	}
+
+	/* remove all mappings */
+	for (i = 0; i < TEST_N_HALF; i++) {
+		OSMO_ASSERT(llist_len(&map->mappings) == (TEST_N - 2*i));
+
+		nr_t orig = TEST_I + i;
+		nr_mapping_del(nr_map_get(map, origin1, orig));
+		nr_mapping_del(nr_map_get(map, origin2, orig));
+	}
+	OSMO_ASSERT(llist_empty(&map->mappings));
+#undef TEST_N
+#undef TEST_I
+}
+
+static int seqmap_is(struct nr_map *map, const char *str)
+{
+	static char buf[4096];
+	char *pos = buf;
+	size_t len = sizeof(buf);
+	struct nr_mapping *m;
+	llist_for_each_entry(m, &map->mappings, entry) {
+		size_t wrote = snprintf(pos, len, "(%d->%d@%d), ",
+					(int)m->orig,
+					(int)m->repl,
+					(int)m->expiry);
+		OSMO_ASSERT(wrote < len);
+		pos += wrote;
+		len -= wrote;
+	}
+	*pos = '\0';
+
+	if (strncmp(buf, str, sizeof(buf)) != 0) {
+		printf("FAILURE: seqmap_is() mismatches expected value:\n"
+		       "expected: %s\n"
+		       "is:       %s\n",
+		       str, buf);
+		return 0;
+	}
+	return 1;
+}
+
+static void test_nr_map_expiry(void)
+{
+	struct nr_map_expiry expiry;
+	struct nr_pool pool;
+	struct nr_map map;
+	int i;
+
+	nr_map_expiry_init(&expiry, 30);
+	nr_pool_init(&pool);
+	nr_map_init(&map, &pool, &expiry);
+	OSMO_ASSERT(seqmap_is(&map, ""));
+
+	/* tick on empty map */
+	OSMO_ASSERT(nr_map_expiry_tick(&expiry, 10000) == 0);
+	OSMO_ASSERT(seqmap_is(&map, ""));
+
+#define MAP1 \
+	"(10->1@10040), " \
+	""
+
+#define MAP2 \
+	"(20->2@10050), " \
+	"(21->3@10051), " \
+	"(22->4@10052), " \
+	"(23->5@10053), " \
+	"(24->6@10054), " \
+	"(25->7@10055), " \
+	"(26->8@10056), " \
+	"(27->9@10057), " \
+	""
+
+#define MAP3 \
+	"(420->10@10072), " \
+	"(421->11@10072), " \
+	"(422->12@10072), " \
+	"(423->13@10072), " \
+	"(424->14@10072), " \
+	"(425->15@10072), " \
+	"(426->16@10072), " \
+	"(427->17@10072), " \
+	""
+
+	/* add mapping at time 10010. */
+	nr_map_have(&map, 0, 10, 10010);
+	OSMO_ASSERT(seqmap_is(&map, MAP1));
+
+	/* tick on unexpired item. */
+	OSMO_ASSERT(nr_map_expiry_tick(&expiry, 10010) == 0);
+	OSMO_ASSERT(nr_map_expiry_tick(&expiry, 10011) == 0);
+	OSMO_ASSERT(seqmap_is(&map, MAP1));
+
+	/* Spread mappings at 10020, 10021, ... 10027. */
+	for (i = 0; i < 8; i++)
+		nr_map_have(&map, 0, 20 + i, 10020 + i);
+	OSMO_ASSERT(seqmap_is(&map, MAP1 MAP2));
+
+	/* tick on unexpired items. */
+	OSMO_ASSERT(nr_map_expiry_tick(&expiry, 10030) == 0);
+	OSMO_ASSERT(nr_map_expiry_tick(&expiry, 10039) == 0);
+	OSMO_ASSERT(seqmap_is(&map, MAP1 MAP2));
+
+	/* expire the first item (from 10010). */
+	OSMO_ASSERT(nr_map_expiry_tick(&expiry, 10010 + 30) == 1);
+	OSMO_ASSERT(seqmap_is(&map, MAP2));
+
+	/* again nothing to expire */
+	OSMO_ASSERT(nr_map_expiry_tick(&expiry, 10041) == 0);
+	OSMO_ASSERT(seqmap_is(&map, MAP2));
+
+	/* Mappings all at the same time. */
+	for (i = 0; i < 8; i++)
+		nr_map_have(&map, 0, 420 + i, 10042);
+	OSMO_ASSERT(seqmap_is(&map, MAP2 MAP3));
+
+	/* Eight to expire, were added further above to be chronologically
+	 * correct, at 10020..10027. */
+	OSMO_ASSERT(nr_map_expiry_tick(&expiry, 10027 + 30) == 8);
+	OSMO_ASSERT(seqmap_is(&map, MAP3));
+
+	/* again nothing to expire */
+	OSMO_ASSERT(nr_map_expiry_tick(&expiry, 10027 + 30) == 0);
+	OSMO_ASSERT(seqmap_is(&map, MAP3));
+
+	/* Eight to expire, from 10042. Now at 10042 + 30: */
+	OSMO_ASSERT(nr_map_expiry_tick(&expiry, 10042 + 30) == 8);
+	OSMO_ASSERT(seqmap_is(&map, ""));
+
+#undef MAP1
+#undef MAP2
+#undef MAP3
+}
+
+
+
+/* override, requires '-Wl,--wrap=gtphub_resolve_ggsn_addr' */
+int __real_gtphub_resolve_ggsn_addr(struct gtphub *hub,
+				    struct osmo_sockaddr *result,
+				    struct gtp_packet_desc *p);
+
+struct osmo_sockaddr resolved_ggsn_addr = {.l = 0};
+int __wrap_gtphub_resolve_ggsn_addr(struct gtphub *hub,
+				    struct osmo_sockaddr *result,
+				    struct gtp_packet_desc *p)
+{
+	osmo_sockaddr_copy(result, &resolved_ggsn_addr);
+	printf("Wrap: returning GGSN addr: %s\n",
+	       osmo_sockaddr_to_str(result));
+	return (resolved_ggsn_addr.l != 0)? 0 : -1;
+}
+
+#define buf_len 1024
+static uint8_t buf[buf_len];
+
+static unsigned int msg(const char *hex)
+{
+	unsigned int l = osmo_hexparse(hex, buf, buf_len);
+	OSMO_ASSERT(l > 0);
+	return l;
+}
+
+/* Compare static buf to given string constant. The amount of bytes is obtained
+ * from parsing the GTP header in buf.  hex must match an osmo_hexdump() of the
+ * desired message. Return 1 if size and content match. */
+#define msg_is(MSG) _msg_is(MSG, __FILE__, __LINE__)
+static int _msg_is(const char *hex, const char *file, int line)
+{
+	struct gtp1_header_long *h = (void*)buf;
+	int len = ntoh16(h->length) + 8;
+	const char *dump = osmo_hexdump_nospc(buf, len);
+	int cmp = strcmp(dump, hex);
+
+	if (cmp != 0) {
+		printf("\n%s:%d: msg_is(): MISMATCH\n"
+		       "  expecting:\n'%s'\n"
+		       "        got:\n'%s'\n",
+		       file,
+		       line,
+		       hex, dump);
+		int i;
+		int l = strlen(hex);
+		int m = strlen(dump);
+		if (m < l)
+			l = m;
+		for (i = 0; i < l; i++) {
+			if (hex[i] != dump[i]) {
+				printf("First mismatch at position %d:\n"
+				       "  %s\n  %s\n", i, hex + i, dump + i);
+				break;
+			}
+		}
+	}
+	return cmp == 0;
+}
+
+#define same_addr(GOT, EXPECTED) _same_addr((GOT),(EXPECTED), __FILE__, __LINE__)
+static int _same_addr(const struct osmo_sockaddr *got,
+		      const struct osmo_sockaddr *expected,
+		      const char *file, int line)
+{
+	int cmp = osmo_sockaddr_cmp(got, expected);
+	if (!cmp)
+		return 1;
+	char buf[256];
+	printf("\n%s:%d: addr_is(): MISMATCH\n"
+	       "  expecting: '%s'\n"
+	       "        got: '%s'\n",
+	       file, line,
+	       osmo_sockaddr_to_str(expected),
+	       osmo_sockaddr_to_strb(got, buf, sizeof(buf)));
+	return 0;
+}
+
+static void test_echo(void)
+{
+	struct gtphub _hub;
+	struct gtphub *hub = &_hub;
+
+	gtphub_init(hub);
+
+	const char *gtp_ping_from_sgsn =
+		"32"	/* 0b001'1 0010: version 1, protocol GTP, with seq nr. */
+		"01"	/* type 01: Echo request */
+		"0004"	/* length of 4 after header TEI */
+		"00000000" /* header TEI == 0 in Echo */
+		"abcd"	/* some 16 octet sequence nr */
+		"0000"	/* N-PDU 0, no extension header (why is this here?) */
+		;
+
+	/* Same with mapped sequence number */
+	const char *gtp_ping_to_ggsn =
+		"32" "01" "0004" "00000000"
+		"6d31"	/* mapped seq */
+		"00" "00";
+
+	const char *gtp_pong_from_ggsn =
+		"32"
+		"02"	/* type 02: Echo response */
+		"0006"	/* len */
+		"00000000" /* tei */
+		"6d31"	/* mapped seq */
+		"0000"	/* ext */
+		"0e01"	/* 0e: Recovery, val == 1 */
+		;
+	/* Same with unmapped sequence number */
+	const char *gtp_pong_to_sgsn =
+		"32" "02" "0006" "00000000"
+		"abcd"	/* unmapped seq */
+		"00" "00" "0e01";
+
+	/* Set the GGSN address that gtphub is forced to resolve to. */
+	OSMO_ASSERT(osmo_sockaddr_init_udp(&resolved_ggsn_addr,
+					   "192.168.43.34", 434)
+		    == 0);
+
+	/* according to spec, we'd always send to port 2123 instead...
+	struct osmo_sockaddr ggsn_standard_port;
+	OSMO_ASSERT(osmo_sockaddr_init_udp(&ggsn_standard_port,
+					   "192.168.43.34", 2123)
+		    == 0);
+	 */
+
+	struct osmo_sockaddr orig_sgsn_addr;
+	OSMO_ASSERT(osmo_sockaddr_init(&orig_sgsn_addr,
+				       AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP,
+				       "192.168.42.23", 423) == 0);
+	struct osmo_fd *ggsn_ofd = NULL;
+	struct osmo_sockaddr *ggsn_addr = NULL;
+	int send;
+	send = gtphub_from_sgsns_handle_buf(hub, GTPH_PORT_CTRL, &orig_sgsn_addr,
+					    buf, msg(gtp_ping_from_sgsn),
+					    &ggsn_ofd, &ggsn_addr);
+	OSMO_ASSERT(send > 0);
+	OSMO_ASSERT(ggsn_addr);
+	OSMO_ASSERT(same_addr(ggsn_addr, &resolved_ggsn_addr));
+	OSMO_ASSERT(msg_is(gtp_ping_to_ggsn));
+
+	struct osmo_fd *sgsn_ofd;
+	struct osmo_sockaddr *sgsn_addr;
+	send = gtphub_from_ggsns_handle_buf(hub, GTPH_PORT_CTRL, ggsn_addr,
+					    buf, msg(gtp_pong_from_ggsn),
+					    &sgsn_ofd, &sgsn_addr);
+	OSMO_ASSERT(send > 0);
+	OSMO_ASSERT(sgsn_addr);
+	OSMO_ASSERT(same_addr(sgsn_addr, &orig_sgsn_addr));
+	OSMO_ASSERT(msg_is(gtp_pong_to_sgsn));
+
+	gtphub_gc(hub, EXPIRE_ALL);
+}
+
+static void test_create_pdp_ctx(void)
+{
+	struct gtphub _hub;
+	struct gtphub *hub = &_hub;
+
+	gtphub_init(hub);
+
+	/* This is copied from a packet that sgsnemu sends. */
+	const char *gtp_req_from_sgsn =
+		"32" 	/* 0b001'1 0010: version 1, protocol GTP, with seq nr. */
+		"10" 	/* type 16: Create PDP Context Request */
+		"0067"	/* length = 8 + 103 */
+		"00000000" /* No TEI yet */
+		"abcd"	/* Sequence nr */
+		"00"	/* N-PDU 0 */
+		"00"	/* No extensions */
+		/* IEs */
+		"02"	/* 2 = IMSI */
+		  "42000121436587f9"
+		"0e" "60" /* 14: Recovery = 96 */
+		"0f01"	/* 15: Selection mode = MS provided APN, subscription not verified*/
+		"10"	/* 16: TEI Data I */
+		  "00000123"
+		"11"	/* 17: TEI Control Plane */
+		  "00000321"
+		"1400"	/* 20: NSAPI = 0*/
+		"1a"	/* 26: Charging Characteristics */
+		  "0800"
+		"80"	/* 128: End User Address */
+		  "0002" /* length = 2: empty PDP Address */
+		  "f121" /* spare 0xf0, PDP organization 1, PDP type number 0x21 = 33 */
+		"83"	/* 131: Access Point Name */
+		  "0008" /* length = 8 */
+		  "696e7465726e6574" /* "internet" */
+		"84"	/* 132: Protocol Configuration Options */
+		  "0015" /* length = 21 */
+		  "80c0231101010011036d69670868656d6d656c6967"
+		"85"	/* 133: GSN Address */
+		  "0004" /* length */
+		  "7f000001"
+		"85"	/* 133: GSN Address (second entry) */
+		  "0004" /* length */
+		  "7f000001"
+		"86"	/* 134: MS International PSTN/ISDN Number (MSISDN) */
+		  "0007" /* length */
+		  "916407123254f6" /* 1946702123456(f) */
+		"87"	/* 135: Quality of Service (QoS) Profile */
+		  "0004" /* length */
+		  "00"	/* priority */
+		  "0b921f" /* QoS profile data */
+		;
+
+	const char *gtp_req_to_ggsn =
+		"32" "10" "0067" "00000000"
+		"6d31"	/* mapped seq ("abcd") */
+		"00" "00" "02" "42000121436587f9" "0e60" "0f01"
+		"10" "00000001" /* mapped TEI Data I ("123") */
+		"11" "00000001" /* mapped TEI Control ("321") */
+		"1400" "1a" "0800" "80" "0002" "f121" "83"
+		"0008" "696e7465726e6574" "84" "0015"
+		"80c0231101010011036d69670868656d6d656c6967" "85" "0004"
+		"7f000001" "85" "0004" "7f000001" "86" "0007" "916407123254f6"
+		"87" "0004" "00" "0b921f"
+		;
+
+	const char *gtp_resp_from_ggsn =
+		"32"
+		"11"	/* Create PDP Context Response */
+		"004e"	/* length = 78 + 8 */
+		"00000001" /* destination TEI (sent in req above) */
+		"6d31"	/* mapped seq */
+		"00" "00"
+		/* IEs */
+		"01"	/* 1: Cause */
+		  "80"	/* value = 0b10000000 = response, no rejection. */
+		"08"	/* 8: Reordering Required */
+		  "00"	/* not required. */
+		"0e" "01" /* 14: Recovery = 1 */
+		"10"	/* 16: TEI Data I */
+		  "00000567"
+		"11"	/* 17: TEI Control */
+		  "00000765"
+		"7f"	/* 127: Charging ID */
+		  "00000001"
+		"80"	/* 128: End User Address */
+		  "0006" /* length = 6 */
+		  "f121" /* spare 0xf0, PDP organization 1, PDP type number 0x21 = 33 */
+		  "7f000002"
+		"84"	/* 132: Protocol Configuration Options */
+		  "0014" /* len = 20 */
+		  "8080211002000010810608080808830600000000"
+		"85"	/* 133: GSN Address */
+		  "0004" /* length */
+		  "7f000002"
+		"85"	/* 133: GSN Address (again) */
+		  "0004" /* length */
+		  "7f000002"
+		"87"	/* 135: Quality of Service (QoS) Profile */
+		  "0004" /* length */
+		  "00"	/* priority */
+		  "0b921f" /* QoS profile data */
+		;
+
+	const char *gtp_resp_to_sgsn =
+		"32" "11" "004e"
+		"00000321" /* unmapped TEI ("001") */
+		"abcd" /* unmapped seq ("6d31") */
+		"00" "00" "01" "80" "08" "00" "0e" "01"
+		"10" "00000001" /* mapped TEI from GGSN ("567") */
+		"11" "00000001" /* mapped TEI from GGSN ("765") */
+		"7f" "00000001" "80" "0006" "f121" "7f000002" "84" "0014"
+		"8080211002000010810608080808830600000000" "85" "0004"
+		"7f000002" "85" "0004" "7f000002" "87" "0004" "00" "0b921f"
+		;
+
+	/* Set the GGSN address that gtphub is forced to resolve to. */
+	OSMO_ASSERT(osmo_sockaddr_init_udp(&resolved_ggsn_addr,
+					   "192.168.43.34", 434)
+		    == 0);
+
+	struct osmo_sockaddr orig_sgsn_addr;
+	OSMO_ASSERT(osmo_sockaddr_init(&orig_sgsn_addr,
+				       AF_UNSPEC, SOCK_DGRAM, IPPROTO_UDP,
+				       "192.168.42.23", 423) == 0);
+	struct osmo_fd *ggsn_ofd = NULL;
+	struct osmo_sockaddr *ggsn_addr = NULL;
+	int send;
+	send = gtphub_from_sgsns_handle_buf(hub, GTPH_PORT_CTRL, &orig_sgsn_addr,
+					    buf, msg(gtp_req_from_sgsn),
+					    &ggsn_ofd, &ggsn_addr);
+	OSMO_ASSERT(send > 0);
+	OSMO_ASSERT(ggsn_addr);
+	OSMO_ASSERT(same_addr(ggsn_addr, &resolved_ggsn_addr));
+	OSMO_ASSERT(msg_is(gtp_req_to_ggsn));
+
+	struct osmo_fd *sgsn_ofd;
+	struct osmo_sockaddr *sgsn_addr;
+	send = gtphub_from_ggsns_handle_buf(hub, GTPH_PORT_CTRL, ggsn_addr,
+					    buf, msg(gtp_resp_from_ggsn),
+					    &sgsn_ofd, &sgsn_addr);
+	OSMO_ASSERT(send > 0);
+	OSMO_ASSERT(sgsn_addr);
+	OSMO_ASSERT(same_addr(sgsn_addr, &orig_sgsn_addr));
+	OSMO_ASSERT(msg_is(gtp_resp_to_sgsn));
+
+	gtphub_gc(hub, EXPIRE_ALL);
+}
+
+static struct log_info_cat gtphub_categories[] = {
+	[DGTPHUB] = {
+		.name = "DGTPHUB",
+		.description = "GTP Hub",
+		.color = "\033[1;33m",
+		.enabled = 1, .loglevel = LOGL_NOTICE,
+	},
+};
+
+static struct log_info info = {
+	.cat = gtphub_categories,
+	.num_cat = ARRAY_SIZE(gtphub_categories),
+};
+
+int main(int argc, char **argv)
+{
+	osmo_init_logging(&info);
+	osmo_gtphub_ctx = talloc_named_const(NULL, 0, "osmo_gtphub");
+
+	test_nr_map_basic();
+	test_nr_map_expiry();
+	test_echo();
+	test_create_pdp_ctx();
+	printf("Done\n");
+
+	talloc_report_full(osmo_gtphub_ctx, stderr);
+	OSMO_ASSERT(talloc_total_blocks(osmo_gtphub_ctx) == 1);
+	return 0;
+}
+
diff --git a/openbsc/tests/gtphub/gtphub_test.ok b/openbsc/tests/gtphub/gtphub_test.ok
new file mode 100644
index 0000000..7be13fe
--- /dev/null
+++ b/openbsc/tests/gtphub/gtphub_test.ok
@@ -0,0 +1,3 @@
+Wrap: returning GGSN addr: 192.168.43.34 port 434
+Wrap: returning GGSN addr: 192.168.43.34 port 434
+Done
diff --git a/openbsc/tests/gtphub/hex2bin.py b/openbsc/tests/gtphub/hex2bin.py
new file mode 100755
index 0000000..6a906b1
--- /dev/null
+++ b/openbsc/tests/gtphub/hex2bin.py
@@ -0,0 +1,13 @@
+#!/usr/bin/env python
+
+import sys
+
+blob = []
+
+for l in sys.stdin.readlines():
+  l = ''.join(c for c in l if not c.isspace())
+
+  for i in range(0, len(l), 2):
+    h = l[i:i+2]
+    sys.stdout.write(chr(int(h, 16)))
+
diff --git a/openbsc/tests/testsuite.at b/openbsc/tests/testsuite.at
index 78aa47e..3a5883e 100644
--- a/openbsc/tests/testsuite.at
+++ b/openbsc/tests/testsuite.at
@@ -110,3 +110,15 @@ AT_CHECK([test "$enable_oap_test" != no || exit 77])
 cat $abs_srcdir/oap/oap_test.ok > expout
 AT_CHECK([$abs_top_builddir/tests/oap/oap_test], [], [expout], [ignore])
 AT_CLEANUP
+
+AT_SETUP([gtphub])
+AT_KEYWORDS([gtphub])
+AT_CHECK([test "$enable_gtphub_test" != no || exit 77])
+cat $abs_srcdir/gtphub/gtphub_test.ok > expout
+AT_CHECK([$abs_top_builddir/tests/gtphub/gtphub_test], [], [expout], [ignore])
+cat $abs_srcdir/gtphub/gtphub_nc_test.ok > expout
+cat $abs_srcdir/gtphub/gtphub_nc_test.gtphub.conf > gtphub.conf
+ln -s $abs_srcdir/gtphub/hex2bin.py .
+ln -s $abs_top_builddir/src/gprs/osmo-gtphub .
+AT_CHECK([$abs_top_builddir/tests/gtphub/gtphub_nc_test.sh], [], [expout], [ignore])
+AT_CLEANUP
