diff --git a/net.c b/net.c
index 0707188..35ec2ae 100644
--- a/net.c
+++ b/net.c
@@ -933,6 +933,10 @@ static const struct {
                 .name = "droplog",
                 .type = QEMU_OPT_STRING,
                 .help = "Set log filename for the reverse firewall",
+            }, {
+                .name = "allow",
+                .type = QEMU_OPT_STRING,
+                .help = "Add an allow rule for the reverse firewall",
             },
             { /* end of list */ }
         },
diff --git a/net/slirp.c b/net/slirp.c
index 07e1353..51e4728 100644
--- a/net/slirp.c
+++ b/net/slirp.c
@@ -34,6 +34,12 @@
 #include "qemu_socket.h"
 #include "slirp/libslirp.h"

+int slirp_add_allow(Slirp *slirp, const char *optarg);
+
+int parse_port_range(const char *str,
+                     unsigned short *lport,
+                     unsigned short *hport);
+
 static int get_str_sep(char *buf, int buf_size, const char **pp, int sep)
 {
     const char *p, *p1;
@@ -58,6 +64,7 @@ static int get_str_sep(char *buf, int buf_size, const char
**pp, int sep)

 #define SLIRP_CFG_HOSTFWD 1
 #define SLIRP_CFG_LEGACY  2
+#define SLIRP_CFG_ALLOW   4

 struct slirp_config_str {
     struct slirp_config_str *next;
@@ -255,6 +262,9 @@ static int net_slirp_init(VLANState *vlan, const char
*model,
             if (slirp_hostfwd(s, config->str,
                               config->flags & SLIRP_CFG_LEGACY) < 0)
                 goto error;
+        } else if (config->flags & SLIRP_CFG_ALLOW) {
+            if (slirp_add_allow(s->slirp, config->str))
+                goto error;
         } else {
             if (slirp_guestfwd(s, config->str,
                                config->flags & SLIRP_CFG_LEGACY) < 0)
@@ -659,7 +669,9 @@ static int net_init_slirp_configs(const char *name,
const char *value, void *opa
 {
     struct slirp_config_str *config;

-    if (strcmp(name, "hostfwd") != 0 && strcmp(name, "guestfwd") != 0) {
+    if (strcmp(name, "hostfwd") != 0 &&
+        strcmp(name, "guestfwd") != 0 &&
+        strcmp(name, "allow") != 0) {
         return 0;
     }

@@ -669,6 +681,8 @@ static int net_init_slirp_configs(const char *name,
const char *value, void *opa

     if (!strcmp(name, "hostfwd")) {
         config->flags = SLIRP_CFG_HOSTFWD;
+    } else if (!strcmp(name, "allow")) {
+        config->flags = SLIRP_CFG_ALLOW;
     }

     config->next = slirp_configs;
@@ -795,3 +809,98 @@ int net_slirp_parse_legacy(QemuOptsList *opts_list,
const char *optarg, int *ret

     return 1;
 }
+
+/*
+ * Parse a null-terminated string specifying a network port or port range
(e.g.
+ * "[1024-65535]"). In case of a single port, lport and hport are the same.
+ * Returns 0 on success and -1 on error.
+ */
+int parse_port_range(const char *str,
+                     unsigned short *lport,
+                     unsigned short *hport) {
+    unsigned int low = 0, high = 0;
+    char *p, *arg = qemu_strdup(str);
+
+    p = rindex(arg, ']');
+    if ((*arg == '[') & (p != NULL)) {
+        p = arg + 1;   /* skip '[' */
+        low  = atoi(strsep(&p, "-"));
+        if (p == NULL) {    /* '-' is not found. e.g. [port] */
+            high = low;
+        } else {            /* [port-port] */
+            high = atoi(p);
+        }
+    } else {
+        low = atoi(arg);
+        high = low;
+    }
+
+    qemu_free(arg);
+
+    if ((low > 0) && (high > 0) && (low <= high) && (high < 65536)) {
+        *lport = low;
+        *hport = high;
+        return 0;
+    }
+
+    return -1;
+}
+
+/*
+ * Add allow rules for the usermode firewall.
+ */
+int slirp_add_allow(Slirp *slirp, const char *optarg)
+{
+    /*
+     * we expect the following format:
+     *  dst_addr:dst_port OR dst_addr:[dst_lport-dst_hport]
+     */
+    char *argument = strdup(optarg), *p = argument;
+    char *dst_addr_str, *dst_port_str;
+    struct in_addr dst_addr;
+    unsigned short dst_lport, dst_hport;
+    char *proto_str;
+    u_int8_t proto;
+
+    proto_str = strsep(&p, ":");
+    if (!strcmp(proto_str, "udp")) {
+        proto = IPPROTO_UDP;
+    } else {
+        fprintf(stderr,
+                "Invalid argument: %s. "
+                "Protocol name is missing or not recognized.\n",
+                optarg);
+        return -1;
+    }
+    dst_addr_str = strsep(&p, ":");
+    dst_port_str = p;
+
+    if (dst_addr_str == NULL || dst_port_str == NULL) {
+        fprintf(stderr,
+                "Invalid argument: %s. "
+                "proto:dst_addr:dst_port or "
+                "proto:dst_addr:[dst_lport-dst_hport]\n",
+                optarg);
+        return -1;
+    }
+
+    /* handling ":port" notation (when IP address is omitted entirely). */
+    if (*dst_addr_str == '\0') {
+        dst_addr.s_addr = 0;
+    } else if (inet_aton(dst_addr_str, &dst_addr) == 0) {
+        fprintf(stderr, "Invalid destination IP address: %s\n",
dst_addr_str);
+        return -1;
+    }
+
+    if (parse_port_range(dst_port_str, &dst_lport, &dst_hport) == -1) {
+        fprintf(stderr,
+                "Invalid destination port or port range: %s.\n",
+                optarg);
+        return -1;
+    }
+
+    slirp_add_allow_internal(slirp, dst_addr, dst_lport, dst_hport, proto);
+
+    free(argument);
+    return 0;
+}
diff --git a/qemu-options.hx b/qemu-options.hx
index 7a8872b..b536f82 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1067,9 +1067,10 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
 #ifdef CONFIG_SLIRP
     "-net
user[,vlan=n][,name=str][,net=addr[/mask]][,host=addr][,restrict=y|n]\n"
     "
[,hostname=host][,dhcpstart=addr][,dns=addr][,tftp=dir][,bootfile=f]\n"
-    "
[,hostfwd=rule][,guestfwd=rule][,drop=udp|all][,droplog=file]"
+    "
[,hostfwd=rule][,guestfwd=rule][,drop=udp|all][,droplog=file]\n"
+    "         [,allow=rule]\n"
 #ifndef _WIN32
-
"[,smb=dir[,smbserver=addr]]\n"
+    "         [,smb=dir[,smbserver=addr]]\n"
 #endif
     "                connect the user mode network stack to VLAN 'n',
configure its\n"
     "                DHCP server and enabled optional services\n"
diff --git a/slirp/libslirp.h b/slirp/libslirp.h
index f1e48a7..1f4ddb1 100644
--- a/slirp/libslirp.h
+++ b/slirp/libslirp.h
@@ -54,6 +54,13 @@ int slirp_should_drop(Slirp *slirp,
                       unsigned short dst_port,
                       u_int8_t proto);

+/* slirp.c */
+void slirp_add_allow_internal(Slirp *slirp,
+                              struct in_addr dst_addr,
+                              unsigned short dst_lport,
+                              unsigned short dst_hport,
+                              u_int8_t proto);
+
 #else /* !CONFIG_SLIRP */

 static inline void slirp_select_fill(int *pnfds, fd_set *readfds,
diff --git a/slirp/slirp.c b/slirp/slirp.c
index 81fd85b..928025e 100644
--- a/slirp/slirp.c
+++ b/slirp/slirp.c
@@ -233,6 +233,7 @@ Slirp *slirp_init(int restricted, struct in_addr
vnetwork,

     slirp->drop = drop;
     slirp->drop_log = drop_log;
+    QSIMPLEQ_INIT(&(slirp->udp_allows));

     slirp->opaque = opaque;

@@ -1126,20 +1127,64 @@ int slirp_should_drop(Slirp *slirp,
                       struct in_addr dst_addr,
                       unsigned short dst_port,
                       u_int8_t proto) {
+    /* struct rfw_allow *allows = NULL; */
+    QSIMPLEQ_HEAD(rfw_allows, rfw_allow) *allows;
+    struct rfw_allow *allow;
+    unsigned short dport;   /* host byte order */
+
     switch (proto) {
     case IPPROTO_UDP:
         if (!(slirp->drop & SLIRP_DROP_UDP)) {
             return 0;
+        } else {
+            allows = (struct rfw_allows*)&slirp->udp_allows;
         }
         break;
     default:
-        return 0;   /* unrecognized protocol. default pass. */
+        return 1;   /* unrecognized protocol. default drop. */
     }

+    /* Find matching allow rule. 0 works as a wildcard for address. */
+    QSIMPLEQ_FOREACH(allow, allows, next) {
+        dport = ntohs(dst_port);
+        if ((allow->dst_lport <= dport) && (dport <= allow->dst_hport)) {
+            /* allow any destination if 0 */
+            if (allow->dst_addr.s_addr == 0
+                || allow->dst_addr.s_addr == dst_addr.s_addr) {
+                return 0;
+            }
+        }
+    }
     return 1;
 }

 /*
+ * Register an allow rule for user mode firewall
+ */
+void slirp_add_allow_internal(Slirp *slirp,
+                              struct in_addr dst_addr,
+                              unsigned short dst_lport,
+                              unsigned short dst_hport,
+                              u_int8_t proto) {
+    struct rfw_allow *allow = qemu_malloc(sizeof(struct rfw_allow));
+
+    allow->dst_addr = dst_addr;
+    allow->dst_lport = dst_lport;
+    allow->dst_hport = dst_hport;
+
+    switch (proto) {
+    case IPPROTO_UDP:
+        QSIMPLEQ_INSERT_HEAD(&(slirp->udp_allows), allow, next);
+        break;
+    case IPPROTO_TCP:
+    default:
+        qemu_free(allow);
+        return;   /* unrecognized protocol */
+    }
+}
+
+
+/*
  * Write to drop-log
  */
 int slirp_drop_log(FILE *drop_log, const char *format, ...)
diff --git a/slirp/slirp.h b/slirp/slirp.h
index d95953c..619bbee 100644
--- a/slirp/slirp.h
+++ b/slirp/slirp.h
@@ -170,6 +170,16 @@ int inet_aton(const char *cp, struct in_addr *ia);
 int qemu_socket(int domain, int type, int protocol);


+struct rfw_allow {
+    /* struct rfw_allow *next; */
+    QSIMPLEQ_ENTRY(rfw_allow) next;
+
+    struct in_addr dst_addr;
+    /* Port range. For a single port, dst_lport = dst_hport. */
+    unsigned short dst_lport;   /* in host byte order */
+    unsigned short dst_hport;   /* in host byte order */
+};
+
 struct Slirp {
     QTAILQ_ENTRY(Slirp) entry;

@@ -183,6 +193,7 @@ struct Slirp {
     /* Reverse Firewall configuration */
     unsigned char drop;
     FILE *drop_log;
+    QSIMPLEQ_HEAD(rfw_allows, rfw_allow) udp_allows;

     /* ARP cache for the guest IP addresses (XXX: allow many entries) */
     uint8_t client_ethaddr[6];
@@ -303,6 +314,7 @@ int tcp_emu(struct socket *, struct mbuf *);
 int tcp_ctl(struct socket *);
 struct tcpcb *tcp_drop(struct tcpcb *tp, int err);

+
 #ifdef USE_PPP
 #define MIN_MRU MINMRU
 #define MAX_MRU MAXMRU
diff --git a/slirp/udp.c b/slirp/udp.c
index 6519d36..5c602d1 100644
--- a/slirp/udp.c
+++ b/slirp/udp.c
@@ -116,7 +116,14 @@ udp_input(register struct mbuf *m, int iphlen)
                 timestamp);
             goto bad;
         } else {
-            /* PASS */
+            slirp_drop_log(
+                slirp->drop_log,
+                "Allowed UDP: src:0x%08x:0x%04hx dst:0x%08x:0x%04hx %ld\n",
+                ntohl(ip->ip_src.s_addr),
+                ntohs(uh->uh_sport),
+                ntohl(ip->ip_dst.s_addr),
+                ntohs(uh->uh_dport),
+                timestamp);
         }

  /*
