[ovs-dev,v3,2/2] northd: Fix direct access to SNAT network.

This change fixes bug that breaks ability of machines from external
networks, to communicate with machines in SNATed networks (specifically
when using a Distributed router).

Currently when a machine (S1) on an external network tries to talk
over TCP with a machine (A1) in a network that has enabled SNAT, the
connection is established successfully. However after the three-way
handshake, any packets that come from the A1 machine will have their
source address translated by the Distributed router, breaking the
communication.

Existing rule in `build_lrouter_out_snat_flow` that decides which
packets should be SNATed already tries to avoid SNATing packets in
reply direction with `(!ct.trk || !ct.rpl)`. However, previous stages
in the distributed LR egress pipeline do not initiate the CT state.

Additionally we need to commit new connections that originate from
external networks into CT, so that the packets in the reply direction
(back to the external network) can be properly identified.

Rationale:

In my original RFC [0], there were questions about the motivation for
fixing this issue. I'll try to summarize why I think this is a bug
that should be fixed.

1. Current implementation for Distributed router already tries to
   avoid SNATing packets in the reply direction, it's just missing
   initialized CT states to make proper decisions.

2. This same scenario works with Gateway Router. I tested with
   following setup:

    foo -- R1 -- join - R3 -- alice
                  |
    bar ----------R2

    R1 is a Distributed router with SNAT for foo. R2 is a Gateway
    router with SNAT for bar. R3 is a Gateway router with no SNAT.
    Using 'alice1' as a client I was able to talk over TCP with
    'bar1' but connection with 'foo1' failed.

3. Regarding security and "leaking" of internal IPs. Reading through
   RFC 4787 [1], 5382 [2] and their update in 7857 [3], the
   specifications do not seem to mandate that SNAT implementations
   must filter incoming traffic destined directly to the internal
   network. Sections like "5. Filtering Behavior" in 4787 and
   "4.3 Externally Initiated Connections" in 5382 describe only
   behavior for traffic destined to external IP/Port associated
   with NAT on the device that performs NAT.

   Besides, with the current implementation, it's already possible
   to scan the internal network with pings and TCP syn scanning.

4. We do have customers/clouds that depend on this functionality.
   This is a scenario that used to work in Openstack with ML2/OVS
   and migrating those clouds to ML2/OVN would break it.

[0]https://mail.openvswitch.org/pipermail/ovs-dev/2024-February/411670.html
[1]https://datatracker.ietf.org/doc/html/rfc4787
[2]https://datatracker.ietf.org/doc/html/rfc5382
[3]https://datatracker.ietf.org/doc/html/rfc7857

Signed-off-by: Martin Kalcok <martin.kalcok@canonical.com>
---
 northd/northd.c         | 66 ++++++++++++++++++++++++++++-------
 northd/ovn-northd.8.xml | 29 ++++++++++++++++
 tests/ovn-northd.at     | 76 +++++++++++++++++++++++++++++++++++++----
 tests/system-ovn.at     | 68 ++++++++++++++++++++++++++++++++++++
 4 files changed, 220 insertions(+), 19 deletions(-)

On Mon, Apr 15, 2024 at 2:15 PM Martin Kalcok <martin.kalcok@canonical.com>
wrote:

> This change fixes bug that breaks ability of machines from external
> networks, to communicate with machines in SNATed networks (specifically
> when using a Distributed router).
>
> Currently when a machine (S1) on an external network tries to talk
> over TCP with a machine (A1) in a network that has enabled SNAT, the
> connection is established successfully. However after the three-way
> handshake, any packets that come from the A1 machine will have their
> source address translated by the Distributed router, breaking the
> communication.
>
> Existing rule in `build_lrouter_out_snat_flow` that decides which
> packets should be SNATed already tries to avoid SNATing packets in
> reply direction with `(!ct.trk || !ct.rpl)`. However, previous stages
> in the distributed LR egress pipeline do not initiate the CT state.
>
> Additionally we need to commit new connections that originate from
> external networks into CT, so that the packets in the reply direction
> (back to the external network) can be properly identified.
>
> Rationale:
>
> In my original RFC [0], there were questions about the motivation for
> fixing this issue. I'll try to summarize why I think this is a bug
> that should be fixed.
>
> 1. Current implementation for Distributed router already tries to
>    avoid SNATing packets in the reply direction, it's just missing
>    initialized CT states to make proper decisions.
>
> 2. This same scenario works with Gateway Router. I tested with
>    following setup:
>
>     foo -- R1 -- join - R3 -- alice
>                   |
>     bar ----------R2
>
>     R1 is a Distributed router with SNAT for foo. R2 is a Gateway
>     router with SNAT for bar. R3 is a Gateway router with no SNAT.
>     Using 'alice1' as a client I was able to talk over TCP with
>     'bar1' but connection with 'foo1' failed.
>
> 3. Regarding security and "leaking" of internal IPs. Reading through
>    RFC 4787 [1], 5382 [2] and their update in 7857 [3], the
>    specifications do not seem to mandate that SNAT implementations
>    must filter incoming traffic destined directly to the internal
>    network. Sections like "5. Filtering Behavior" in 4787 and
>    "4.3 Externally Initiated Connections" in 5382 describe only
>    behavior for traffic destined to external IP/Port associated
>    with NAT on the device that performs NAT.
>
>    Besides, with the current implementation, it's already possible
>    to scan the internal network with pings and TCP syn scanning.
>
> 4. We do have customers/clouds that depend on this functionality.
>    This is a scenario that used to work in Openstack with ML2/OVS
>    and migrating those clouds to ML2/OVN would break it.
>
> [0]
> https://mail.openvswitch.org/pipermail/ovs-dev/2024-February/411670.html
> [1]https://datatracker.ietf.org/doc/html/rfc4787
> [2]https://datatracker.ietf.org/doc/html/rfc5382
> [3]https://datatracker.ietf.org/doc/html/rfc7857
>
> Signed-off-by: Martin Kalcok <martin.kalcok@canonical.com>
> ---
>

Hi Martin,

I have just some nits down below.


>  northd/northd.c         | 66 ++++++++++++++++++++++++++++-------
>  northd/ovn-northd.8.xml | 29 ++++++++++++++++
>  tests/ovn-northd.at     | 76 +++++++++++++++++++++++++++++++++++++----
>  tests/system-ovn.at     | 68 ++++++++++++++++++++++++++++++++++++
>  4 files changed, 220 insertions(+), 19 deletions(-)
>
> diff --git a/northd/northd.c b/northd/northd.c
> index 02cf5b234..0726c8429 100644
> --- a/northd/northd.c
> +++ b/northd/northd.c
> @@ -14413,20 +14413,27 @@ build_lrouter_out_is_dnat_local(struct
> lflow_table *lflows,
>
>  static void
>  build_lrouter_out_snat_match(struct lflow_table *lflows,
> -                             const struct ovn_datapath *od,
> -                             const struct nbrec_nat *nat, struct ds
> *match,
> -                             bool distributed_nat, int cidr_bits, bool
> is_v6,
> -                             struct ovn_port *l3dgw_port,
> -                             struct lflow_ref *lflow_ref)
> +                                         const struct ovn_datapath *od,
> +                                         const struct nbrec_nat *nat,
> +                                         struct ds *match,
> +                                         bool distributed_nat, int
> cidr_bits,
> +                                         bool is_v6,
> +                                         struct ovn_port *l3dgw_port,
> +                                         struct lflow_ref *lflow_ref,
> +                                         bool is_reverse)
>  {
>      ds_clear(match);
>
> -    ds_put_format(match, "ip && ip%c.src == %s", is_v6 ? '6' : '4',
> +    ds_put_format(match, "ip && ip%c.%s == %s",
> +                  is_v6 ? '6' : '4',
> +                  is_reverse ? "dst" : "src",
>                    nat->logical_ip);
>
>      if (!od->is_gw_router) {
>          /* Distributed router. */
> -        ds_put_format(match, " && outport == %s", l3dgw_port->json_key);
> +        ds_put_format(match, " && %s == %s",
> +                      is_reverse ? "inport" : "outport",
> +                      l3dgw_port->json_key);
>          if (od->n_l3dgw_ports) {
>              ds_put_format(match, " && is_chassis_resident(\"%s\")",
>                            distributed_nat
> @@ -14437,7 +14444,7 @@ build_lrouter_out_snat_match(struct lflow_table
> *lflows,
>
>      if (nat->allowed_ext_ips || nat->exempted_ext_ips) {
>          lrouter_nat_add_ext_ip_match(od, lflows, match, nat,
> -                                     is_v6, false, cidr_bits,
> +                                     is_v6, is_reverse, cidr_bits,
>                                       lflow_ref);
>      }
>  }
> @@ -14464,7 +14471,8 @@ build_lrouter_out_snat_stateless_flow(struct
> lflow_table *lflows,
>      uint16_t priority = cidr_bits + 1;
>
>      build_lrouter_out_snat_match(lflows, od, nat, match, distributed_nat,
> -                                 cidr_bits, is_v6, l3dgw_port, lflow_ref);
> +                                 cidr_bits, is_v6, l3dgw_port, lflow_ref,
> +                                 false);
>
>      if (!od->is_gw_router) {
>          /* Distributed router. */
> @@ -14511,7 +14519,7 @@ build_lrouter_out_snat_in_czone_flow(struct
> lflow_table *lflows,
>
>      build_lrouter_out_snat_match(lflows, od, nat, match, distributed_nat,
>                                   cidr_bits, is_v6, l3dgw_port,
> -                                 lflow_ref);
> +                                 lflow_ref, false);
>
>      if (od->n_l3dgw_ports) {
>          priority += 128;
> @@ -14560,7 +14568,8 @@ build_lrouter_out_snat_flow(struct lflow_table
> *lflows,
>                              struct ds *actions, bool distributed_nat,
>                              struct eth_addr mac, int cidr_bits, bool
> is_v6,
>                              struct ovn_port *l3dgw_port,
> -                            struct lflow_ref *lflow_ref)
> +                            struct lflow_ref *lflow_ref,
> +                            const struct chassis_features *features)
>  {
>      if (strcmp(nat->type, "snat") && strcmp(nat->type, "dnat_and_snat")) {
>          return;
> @@ -14574,7 +14583,9 @@ build_lrouter_out_snat_flow(struct lflow_table
> *lflows,
>      uint16_t priority = cidr_bits + 1;
>
>      build_lrouter_out_snat_match(lflows, od, nat, match, distributed_nat,
> -                                 cidr_bits, is_v6, l3dgw_port, lflow_ref);
> +                                 cidr_bits, is_v6, l3dgw_port, lflow_ref,
> +                                 false);
> +    size_t original_match_len = match->length;
>
>      if (!od->is_gw_router) {
>          /* Distributed router. */
> @@ -14599,6 +14610,35 @@ build_lrouter_out_snat_flow(struct lflow_table
> *lflows,
>                              priority, ds_cstr(match),
>                              ds_cstr(actions), &nat->header_,
>                              lflow_ref);
> +
> +    /* For the SNAT networks, we need to make sure that connections are
> +     * properly tracked so we can decide whether to perform SNAT on
> traffic
> +     * exiting the network. */
> +    if (features->ct_commit_to_zone && !strcmp(nat->type, "snat") &&
> +        !od->is_gw_router) {
> +        /* For traffic that comes from SNAT network, initiate CT state
> before
> +         * entering S_ROUTER_OUT_SNAT to allow matching on various CT
> states.
> +         */
> +        ds_truncate(match, original_match_len);
> +        ovn_lflow_add(lflows, od, S_ROUTER_OUT_POST_UNDNAT, 70,
> +                      ds_cstr(match), "ct_snat; ",
>

nit: Extra space after ct_snat;


> +                      lflow_ref);
> +
> +        build_lrouter_out_snat_match(lflows, od, nat, match,
> +                                     distributed_nat, cidr_bits, is_v6,
> +                                     l3dgw_port, lflow_ref, true);
> +
> +        /* New traffic that goes into SNAT network is committed to CT to
> avoid
> +         * SNAT-ing replies.*/
> +        ovn_lflow_add(lflows, od, S_ROUTER_OUT_SNAT, priority,
> +                      ds_cstr(match), "ct_snat;",
> +                      lflow_ref);
> +
> +        ds_put_cstr(match, " && ct.new");
> +        ovn_lflow_add(lflows, od, S_ROUTER_OUT_POST_SNAT, priority,
> +                      ds_cstr(match), "ct_commit_to_zone(snat); next; ",
>

nit: Extra space after next;


> +                      lflow_ref);
> +    }
>  }
>
>  static void
> @@ -15137,7 +15177,7 @@ build_lrouter_nat_defrag_and_lb(
>          } else {
>              build_lrouter_out_snat_flow(lflows, od, nat, match, actions,
>                                          distributed_nat, mac, cidr_bits,
> is_v6,
> -                                        l3dgw_port, lflow_ref);
> +                                        l3dgw_port, lflow_ref, features);
>          }
>
>          /* S_ROUTER_IN_ADMISSION - S_ROUTER_IN_IP_INPUT */
> diff --git a/northd/ovn-northd.8.xml b/northd/ovn-northd.8.xml
> index 90ce0de3f..93a0b781a 100644
> --- a/northd/ovn-northd.8.xml
> +++ b/northd/ovn-northd.8.xml
> @@ -4876,6 +4876,13 @@ nd_ns {
>
>      <p>
>        <ul>
> +        <li>
> +          A priority-70 logical flow is added that initiates CT state for
> +          traffic that is configured to be SNATed on Distributed routers.
> +          This allows the next table, <code>lr_out_snat</code>, to
> +          effectively match on various CT states.
> +        </li>
> +
>          <li>
>            A priority-50 logical flow is added that commits any untracked
> flows
>            from the previous table <code>lr_out_undnat</code> for Gateway
> @@ -5068,6 +5075,18 @@ nd_ns {
>
>        </li>
>
> +      <li>
> +        An additional flow is added for traffic that goes in opposite
> +        direction (i.e. it enters a network with configured SNAT). Where
> the
> +        flow above matched on <code>ip4.src == <var>A</var> &amp;&amp;
> outport
> +        == <var>GW</var></code>, this flow matches on <code> ip4.dst ==
> +        <var>A</var> &amp;&amp; inport == <var>GW</var></code>. A CT
> state is
> +        initiated for this traffic so that the following table, <code>
> +        lr_out_post_snat</code>, can identify whether the traffic flow was
> +        initiated from the internal or external network.
> +
> +      </li>
> +
>        <li>
>          A priority-0 logical flow with match <code>1</code> has actions
>          <code>next;</code>.
> @@ -5079,6 +5098,16 @@ nd_ns {
>      <p>
>        Packets reaching this table are processed according to the flows
> below:
>        <ul>
> +        <li>
> +          Traffic that goes directly into a network configured with SNAT
> on
> +          Distributed routers, and was initiated from an external network
> (i.e.
> +          it matches <code>ct.new</code>), is committed to the SNAT CT
> zone.
> +          This ensures that replies returning from the SNATed network do
> not
> +          have their source address translated. For details about match
> rules
> +          and priority see section "Egress Table 3: SNAT on Distributed
> +          Routers".
> +        </li>
> +
>          <li>
>            A priority-0 logical flow that matches all packets not already
>            handled (match <code>1</code>) and action <code>next;</code>.
> diff --git a/tests/ovn-northd.at b/tests/ovn-northd.at
> index be006fb32..3c9d9309b 100644
> --- a/tests/ovn-northd.at
> +++ b/tests/ovn-northd.at
> @@ -1107,7 +1107,8 @@ ovn_start
>  #
>  # DR is connected to S1 and CR is connected to S2
>
> -check ovn-sbctl chassis-add gw1 geneve 127.0.0.1
> +check ovn-sbctl chassis-add gw1 geneve 127.0.0.1 \
> +  -- set chassis gw1 other_config:ct-commit-to-zone="true"
>
>  check ovn-nbctl lr-add DR
>  check ovn-nbctl lrp-add DR DR-S1 02:ac:10:01:00:01 172.16.1.1/24
> @@ -1155,15 +1156,24 @@ AT_CAPTURE_FILE([crflows])
>  AT_CHECK([grep -e "lr_out_snat" drflows | ovn_strip_lflows], [0], [dnl
>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
> action=(next;)
> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
> 50.0.0.11 && inport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
> ip4.src == $allowed_range), action=(ct_snat;)
>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
> 50.0.0.11 && outport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
> ip4.dst == $allowed_range && (!ct.trk || !ct.rpl)),
> action=(ct_snat(172.16.1.1);)
>  ])
>
> +AT_CHECK([grep -e "lr_out_post_snat" drflows | ovn_strip_lflows], [0],
> [dnl
> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
> 50.0.0.11 && inport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
> ip4.src == $allowed_range && ct.new), action=(ct_commit_to_zone(snat);
> next; )
> +])
> +
>  AT_CHECK([grep -e "lr_out_snat" crflows | ovn_strip_lflows], [0], [dnl
>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
> action=(next;)
>    table=??(lr_out_snat        ), priority=33   , match=(ip && ip4.src ==
> 50.0.0.11 && ip4.dst == $allowed_range && (!ct.trk || !ct.rpl)),
> action=(ct_snat(172.16.1.1);)
>  ])
>
> +AT_CHECK([grep -e "lr_out_post_snat" crflows | ovn_strip_lflows], [0],
> [dnl
> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
> +])
>
>  # SNAT with DISALLOWED_IPs
>  check ovn-nbctl lr-nat-del DR snat  50.0.0.11
> @@ -1185,10 +1195,16 @@ AT_CAPTURE_FILE([crflows2])
>  AT_CHECK([grep -e "lr_out_snat" drflows2 | ovn_strip_lflows], [0], [dnl
>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
> action=(next;)
> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
> 50.0.0.11 && inport == "DR-S1" && is_chassis_resident("cr-DR-S1")),
> action=(ct_snat;)
>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
> 50.0.0.11 && outport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
> (!ct.trk || !ct.rpl)), action=(ct_snat(172.16.1.1);)
>    table=??(lr_out_snat        ), priority=163  , match=(ip && ip4.src ==
> 50.0.0.11 && outport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
> ip4.dst == $disallowed_range), action=(next;)
>  ])
>
> +AT_CHECK([grep -e "lr_out_post_snat" drflows2 | ovn_strip_lflows], [0],
> [dnl
> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
> 50.0.0.11 && inport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
> ct.new), action=(ct_commit_to_zone(snat); next; )
> +])
> +
>  AT_CHECK([grep -e "lr_out_snat" crflows2 | ovn_strip_lflows], [0], [dnl
>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
> action=(next;)
> @@ -1196,6 +1212,10 @@ AT_CHECK([grep -e "lr_out_snat" crflows2 |
> ovn_strip_lflows], [0], [dnl
>    table=??(lr_out_snat        ), priority=35   , match=(ip && ip4.src ==
> 50.0.0.11 && ip4.dst == $disallowed_range), action=(next;)
>  ])
>
> +AT_CHECK([grep -e "lr_out_post_snat" crflows2 | ovn_strip_lflows], [0],
> [dnl
> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
> +])
> +
>  # Stateful FIP with ALLOWED_IPs
>  check ovn-nbctl lr-nat-del DR snat  50.0.0.11
>  check ovn-nbctl lr-nat-del CR snat  50.0.0.11
> @@ -1217,12 +1237,20 @@ AT_CHECK([grep -e "lr_out_snat" drflows3 |
> ovn_strip_lflows], [0], [dnl
>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
> 50.0.0.11 && outport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
> ip4.dst == $allowed_range && (!ct.trk || !ct.rpl)),
> action=(ct_snat(172.16.1.2);)
>  ])
>
> +AT_CHECK([grep -e "lr_out_post_snat" drflows3 | ovn_strip_lflows], [0],
> [dnl
> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
> +])
> +
>  AT_CHECK([grep -e "lr_out_snat" crflows3 | ovn_strip_lflows], [0], [dnl
>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
> action=(next;)
>    table=??(lr_out_snat        ), priority=33   , match=(ip && ip4.src ==
> 50.0.0.11 && ip4.dst == $allowed_range && (!ct.trk || !ct.rpl)),
> action=(ct_snat(172.16.1.2);)
>  ])
>
> +AT_CHECK([grep -e "lr_out_post_snat" crflows3 | ovn_strip_lflows], [0],
> [dnl
> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
> +])
> +
>  # Stateful FIP with DISALLOWED_IPs
>  ovn-nbctl lr-nat-del DR dnat_and_snat  172.16.1.2
>  ovn-nbctl lr-nat-del CR dnat_and_snat  172.16.1.2
> @@ -1279,7 +1307,7 @@ AT_CHECK([grep -e "lr_out_snat" crflows5 |
> ovn_strip_lflows], [0], [dnl
>    table=??(lr_out_snat        ), priority=33   , match=(ip && ip4.src ==
> 50.0.0.11 && ip4.dst == $allowed_range), action=(ip4.src=172.16.1.2; next;)
>  ])
>
> -# Stateful FIP with DISALLOWED_IPs
> +# Stateless FIP with DISALLOWED_IPs
>  ovn-nbctl lr-nat-del DR dnat_and_snat  172.16.1.2
>  ovn-nbctl lr-nat-del CR dnat_and_snat  172.16.1.2
>
> @@ -5521,7 +5549,8 @@ AT_CHECK([grep "lr_out_snat" lr0flows |
> ovn_strip_lflows], [0], [dnl
>
>  check ovn-sbctl chassis-add gw1 geneve 127.0.0.1 \
>    -- set chassis gw1 other_config:ct-no-masked-label="true" \
> -  -- set chassis gw1 other_config:ovn-ct-lb-related="true"
> +  -- set chassis gw1 other_config:ovn-ct-lb-related="true" \
> +  -- set chassis gw1 other_config:ct-commit-to-zone="true"
>
>  # Create a distributed gw port on lr0
>  check ovn-nbctl ls-add public
> @@ -5622,16 +5651,26 @@ AT_CHECK([grep "lr_out_undnat" lr0flows |
> ovn_strip_lflows], [0], [dnl
>
>  AT_CHECK([grep "lr_out_post_undnat" lr0flows | ovn_strip_lflows], [0],
> [dnl
>    table=??(lr_out_post_undnat ), priority=0    , match=(1), action=(next;)
> +  table=??(lr_out_post_undnat ), priority=70   , match=(ip && ip4.src ==
> 10.0.0.0/24 && outport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public")), action=(ct_snat; )
> +  table=??(lr_out_post_undnat ), priority=70   , match=(ip && ip4.src ==
> 10.0.0.10 && outport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public")), action=(ct_snat; )
>  ])
>
>  AT_CHECK([grep "lr_out_snat" lr0flows | ovn_strip_lflows], [0], [dnl
>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
> action=(next;)
> +  table=??(lr_out_snat        ), priority=153  , match=(ip && ip4.dst ==
> 10.0.0.0/24 && inport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public")), action=(ct_snat;)
>    table=??(lr_out_snat        ), priority=153  , match=(ip && ip4.src ==
> 10.0.0.0/24 && outport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public") && (!ct.trk || !ct.rpl)),
> action=(ct_snat(172.168.0.10);)
> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
> 10.0.0.10 && inport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public")), action=(ct_snat;)
>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
> 10.0.0.10 && outport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public") && (!ct.trk || !ct.rpl)),
> action=(ct_snat(172.168.0.30);)
>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
> 10.0.0.3 && outport == "lr0-public" && is_chassis_resident("cr-lr0-public")
> && (!ct.trk || !ct.rpl)), action=(ct_snat(172.168.0.20);)
>  ])
>
> +AT_CHECK([grep "lr_out_post_snat" lr0flows | ovn_strip_lflows], [0], [dnl
> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
> +  table=??(lr_out_post_snat   ), priority=153  , match=(ip && ip4.dst ==
> 10.0.0.0/24 && inport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public") && ct.new),
> action=(ct_commit_to_zone(snat); next; )
> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
> 10.0.0.10 && inport == "lr0-public" && is_chassis_resident("cr-lr0-public")
> && ct.new), action=(ct_commit_to_zone(snat); next; )
> +])
> +
>  # Associate load balancer to lr0
>
>  check ovn-nbctl lb-add lb0 172.168.0.100:8082 "10.0.0.50:82,10.0.0.60:82"
> @@ -5770,16 +5809,26 @@ AT_CHECK([grep "lr_out_undnat" lr0flows |
> ovn_strip_lflows], [0], [dnl
>
>  AT_CHECK([grep "lr_out_post_undnat" lr0flows | ovn_strip_lflows], [0],
> [dnl
>    table=??(lr_out_post_undnat ), priority=0    , match=(1), action=(next;)
> +  table=??(lr_out_post_undnat ), priority=70   , match=(ip && ip4.src ==
> 10.0.0.0/24 && outport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public")), action=(ct_snat; )
> +  table=??(lr_out_post_undnat ), priority=70   , match=(ip && ip4.src ==
> 10.0.0.10 && outport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public")), action=(ct_snat; )
>  ])
>
>  AT_CHECK([grep "lr_out_snat" lr0flows | ovn_strip_lflows], [0], [dnl
>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
> action=(next;)
> +  table=??(lr_out_snat        ), priority=153  , match=(ip && ip4.dst ==
> 10.0.0.0/24 && inport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public")), action=(ct_snat;)
>    table=??(lr_out_snat        ), priority=153  , match=(ip && ip4.src ==
> 10.0.0.0/24 && outport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public") && (!ct.trk || !ct.rpl)),
> action=(ct_snat(172.168.0.10);)
> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
> 10.0.0.10 && inport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public")), action=(ct_snat;)
>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
> 10.0.0.10 && outport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public") && (!ct.trk || !ct.rpl)),
> action=(ct_snat(172.168.0.30);)
>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
> 10.0.0.3 && outport == "lr0-public" && is_chassis_resident("cr-lr0-public")
> && (!ct.trk || !ct.rpl)), action=(ct_snat(172.168.0.20);)
>  ])
>
> +AT_CHECK([grep "lr_out_post_snat" lr0flows | ovn_strip_lflows], [0], [dnl
> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
> +  table=??(lr_out_post_snat   ), priority=153  , match=(ip && ip4.dst ==
> 10.0.0.0/24 && inport == "lr0-public" &&
> is_chassis_resident("cr-lr0-public") && ct.new),
> action=(ct_commit_to_zone(snat); next; )
> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
> 10.0.0.10 && inport == "lr0-public" && is_chassis_resident("cr-lr0-public")
> && ct.new), action=(ct_commit_to_zone(snat); next; )
> +])
> +
>  # Make the logical router as Gateway router
>  check ovn-nbctl clear logical_router_port lr0-public gateway_chassis
>  check ovn-nbctl set logical_router lr0 options:chassis=gw1
> @@ -7606,9 +7655,14 @@ ovn_start
>  # Validate SNAT, DNAT and DNAT_AND_SNAT behavior with multiple
>  # distributed gateway LRPs.
>
> -check ovn-sbctl chassis-add gw1 geneve 127.0.0.1
> -check ovn-sbctl chassis-add gw2 geneve 128.0.0.1
> -check ovn-sbctl chassis-add gw3 geneve 129.0.0.1
> +check ovn-sbctl chassis-add gw1 geneve 127.0.0.1 \
> +  -- set chassis gw1 other_config:ct-commit-to-zone="true"
> +
> +check ovn-sbctl chassis-add gw2 geneve 128.0.0.1 \
> +  -- set chassis gw2 other_config:ct-commit-to-zone="true"
> +
> +check ovn-sbctl chassis-add gw3 geneve 129.0.0.1 \
> +  -- set chassis gw3 other_config:ct-commit-to-zone="true"
>
>  check ovn-nbctl lr-add DR
>  check ovn-nbctl lrp-add DR DR-S1 02:ac:10:01:00:01 172.16.1.1/24
> @@ -7673,11 +7727,21 @@ AT_CHECK([grep lr_in_unsnat lrflows | grep ct_snat
> | ovn_strip_lflows], [0], [dn
>  ])
>
>  AT_CHECK([grep lr_out_snat lrflows | grep ct_snat | ovn_strip_lflows],
> [0], [dnl
> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
> 20.0.0.10 && inport == "DR-S1" && is_chassis_resident("cr-DR-S1")),
> action=(ct_snat;)
> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
> 20.0.0.10 && inport == "DR-S2" && is_chassis_resident("cr-DR-S2")),
> action=(ct_snat;)
> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
> 20.0.0.10 && inport == "DR-S3" && is_chassis_resident("cr-DR-S3")),
> action=(ct_snat;)
>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
> 20.0.0.10 && outport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
> (!ct.trk || !ct.rpl)), action=(ct_snat(172.16.1.10);)
>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
> 20.0.0.10 && outport == "DR-S2" && is_chassis_resident("cr-DR-S2") &&
> (!ct.trk || !ct.rpl)), action=(ct_snat(10.0.0.10);)
>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
> 20.0.0.10 && outport == "DR-S3" && is_chassis_resident("cr-DR-S3") &&
> (!ct.trk || !ct.rpl)), action=(ct_snat(192.168.0.10);)
>  ])
>
> +AT_CHECK([grep lr_out_post_snat lrflows | ovn_strip_lflows], [0], [dnl
> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
> 20.0.0.10 && inport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
> ct.new), action=(ct_commit_to_zone(snat); next; )
> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
> 20.0.0.10 && inport == "DR-S2" && is_chassis_resident("cr-DR-S2") &&
> ct.new), action=(ct_commit_to_zone(snat); next; )
> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
> 20.0.0.10 && inport == "DR-S3" && is_chassis_resident("cr-DR-S3") &&
> ct.new), action=(ct_commit_to_zone(snat); next; )
> +])
> +
>  check ovn-nbctl --wait=sb lr-nat-del DR snat 20.0.0.10
>  AT_CHECK([ovn-sbctl dump-flows DR | grep -e lr_in_unsnat -e lr_out_snat |
> grep ct_snat | wc -l], [0], [0
>  ])
> diff --git a/tests/system-ovn.at b/tests/system-ovn.at
> index c699f7960..68adfa4e6 100644
> --- a/tests/system-ovn.at
> +++ b/tests/system-ovn.at
> @@ -3574,6 +3574,39 @@ NS_CHECK_EXEC([foo1], [ping -q -c 3 -i 0.3 -w 2
> 10.0.0.1 | FORMAT_PING], \
>  3 packets transmitted, 3 received, 0% packet loss, time 0ms
>  ])
>
> +# test_connectivity_from_ext takes parameters 'vm' and 'ip'. It tests
> +# icmp, udp and tcp connectivity from external network to the 'vm' on
> +# the specified 'ip'.
> +test_connectivity_from_ext() {
> +    local vm=$1; shift
> +    local ip=$1; shift
> +
> +    # Start listening daemons for UDP and TCP connections
> +    NETNS_DAEMONIZE($vm, [nc -l -u 1234], [nc-$vm-$ip-udp.pid])
> +    NETNS_DAEMONIZE($vm, [nc -l -k 1235], [nc-$vm-$ip-tcp.pid])
> +
> +    # Ensure that vm can be pinged on the specified IP
> +    NS_CHECK_EXEC([alice1], [ping -q -c 3 -i 0.3 -w 2 $ip | FORMAT_PING],
> \
> +    [0], [dnl
> +3 packets transmitted, 3 received, 0% packet loss, time 0ms
> +])
> +
> +    # Perform two consecutive UDP connections to the specified IP
> +    NS_CHECK_EXEC([alice1], [nc -u $ip 1234 -p 2000 -z])
> +    NS_CHECK_EXEC([alice1], [nc -u $ip 1234 -p 2000 -z])
> +
> +    # Send data over TCP connection to the specified IP
> +    NS_CHECK_EXEC([alice1], [echo "TCP test" | nc --send-only $ip 1235])
> +}
> +
> +# Test access from external network to the internal IP of a VM that
> +# has also configured DNAT
> +test_connectivity_from_ext foo1 192.168.1.2
> +
> +# Test access from external network to the internal IP of a VM that
> +# does not have DNAT
> +test_connectivity_from_ext bar1 192.168.2.2
> +
>  OVS_WAIT_UNTIL([
>      total_pkts=$(cat ext-net.tcpdump | wc -l)
>      test "${total_pkts}" = "3"
> @@ -3740,6 +3773,39 @@ sed -e 's/zone=[[0-9]]*/zone=<cleared>/'], [0], [dnl
>
>  icmpv6,orig=(src=fd12::2,dst=fd20::2,id=<cleared>,type=128,code=0),reply=(src=fd20::2,dst=fd20::1,id=<cleared>,type=129,code=0),zone=<cleared>
>  ])
>
> +# test_connectivity_from_ext takes parameters 'vm' and 'ip'. It tests
> +# icmp, udp and tcp connectivity from external network to the 'vm' on
> +# the specified 'ip'.
> +test_connectivity_from_ext() {
> +    local vm=$1; shift
> +    local ip=$1; shift
> +
> +    # Start listening daemons for UDP and TCP connections
> +    NETNS_DAEMONIZE($vm, [nc -l -u 1234], [nc-$vm-$ip-udp.pid])
> +    NETNS_DAEMONIZE($vm, [nc -l -k 1235], [nc-$vm-$ip-tcp.pid])
> +
> +    # Ensure that vm can be pinged on the specified IP
> +    NS_CHECK_EXEC([alice1], [ping -q -c 3 -i 0.3 -w 2 $ip | FORMAT_PING],
> \
> +    [0], [dnl
> +3 packets transmitted, 3 received, 0% packet loss, time 0ms
> +])
> +
> +    # Perform two consecutive UDP connections to the specified IP
> +    NS_CHECK_EXEC([alice1], [nc -u $ip 1234 -p 2000 -z])
> +    NS_CHECK_EXEC([alice1], [nc -u $ip 1234 -p 2000 -z])
> +
> +    # Send data over TCP connection to the specified IP
> +    NS_CHECK_EXEC([alice1], [echo "TCP test" | nc --send-only $ip 1235])
> +}
> +
> +# Test access from external network to the internal IP of a VM that
> +# has also configured DNAT
> +test_connectivity_from_ext foo1 fd11::2
> +
> +# Test access from external network to the internal IP of a VM that
> +# does not have DNAT
> +test_connectivity_from_ext bar1 fd12::2
> +
>  OVS_APP_EXIT_AND_WAIT([ovn-controller])
>
>  as ovn-sb
> @@ -3920,6 +3986,7 @@ NS_CHECK_EXEC([foo2], [ping -q -c 3 -i 0.3 -w 2
> 172.16.1.4 | FORMAT_PING], \
>  AT_CHECK([ovs-appctl dpctl/dump-conntrack | grep icmp |
> FORMAT_CT(172.16.1.1) | \
>  sed -e 's/zone=[[0-9]]*/zone=<cleared>/'], [0], [dnl
>
>  icmp,orig=(src=172.16.1.1,dst=172.16.1.4,id=<cleared>,type=8,code=0),reply=(src=192.168.2.2,dst=172.16.1.1,id=<cleared>,type=0,code=0),zone=<cleared>
>
> +icmp,orig=(src=172.16.1.1,dst=192.168.2.2,id=<cleared>,type=8,code=0),reply=(src=192.168.2.2,dst=172.16.1.1,id=<cleared>,type=0,code=0),zone=<cleared>
>
>  icmp,orig=(src=192.168.1.3,dst=172.16.1.4,id=<cleared>,type=8,code=0),reply=(src=172.16.1.4,dst=172.16.1.1,id=<cleared>,type=0,code=0),zone=<cleared>
>  ])
>
> @@ -4088,6 +4155,7 @@ NS_CHECK_EXEC([foo2], [ping -q -c 3 -i 0.3 -w 2
> fd20::4 | FORMAT_PING], \
>  AT_CHECK([ovs-appctl dpctl/dump-conntrack | FORMAT_CT(fd20::1) | \
>  sed -e 's/zone=[[0-9]]*/zone=<cleared>/'], [0], [dnl
>
>  icmpv6,orig=(src=fd11::3,dst=fd20::4,id=<cleared>,type=128,code=0),reply=(src=fd20::4,dst=fd20::1,id=<cleared>,type=129,code=0),zone=<cleared>
>
> +icmpv6,orig=(src=fd20::1,dst=fd12::2,id=<cleared>,type=128,code=0),reply=(src=fd12::2,dst=fd20::1,id=<cleared>,type=129,code=0),zone=<cleared>
>
>  icmpv6,orig=(src=fd20::1,dst=fd20::4,id=<cleared>,type=128,code=0),reply=(src=fd12::2,dst=fd20::1,id=<cleared>,type=129,code=0),zone=<cleared>
>  ])
>
> --
> 2.40.1
>
>
Other than that it looks good.

Thanks,
Ales

On 4/17/24 09:08, Ales Musil wrote:
> On Mon, Apr 15, 2024 at 2:15 PM Martin Kalcok <martin.kalcok@canonical.com>
> wrote:
> 
>> This change fixes bug that breaks ability of machines from external
>> networks, to communicate with machines in SNATed networks (specifically
>> when using a Distributed router).
>>
>> Currently when a machine (S1) on an external network tries to talk
>> over TCP with a machine (A1) in a network that has enabled SNAT, the
>> connection is established successfully. However after the three-way
>> handshake, any packets that come from the A1 machine will have their
>> source address translated by the Distributed router, breaking the
>> communication.
>>
>> Existing rule in `build_lrouter_out_snat_flow` that decides which
>> packets should be SNATed already tries to avoid SNATing packets in
>> reply direction with `(!ct.trk || !ct.rpl)`. However, previous stages
>> in the distributed LR egress pipeline do not initiate the CT state.
>>
>> Additionally we need to commit new connections that originate from
>> external networks into CT, so that the packets in the reply direction
>> (back to the external network) can be properly identified.
>>
>> Rationale:
>>
>> In my original RFC [0], there were questions about the motivation for
>> fixing this issue. I'll try to summarize why I think this is a bug
>> that should be fixed.
>>
>> 1. Current implementation for Distributed router already tries to
>>    avoid SNATing packets in the reply direction, it's just missing
>>    initialized CT states to make proper decisions.
>>
>> 2. This same scenario works with Gateway Router. I tested with
>>    following setup:
>>
>>     foo -- R1 -- join - R3 -- alice
>>                   |
>>     bar ----------R2
>>
>>     R1 is a Distributed router with SNAT for foo. R2 is a Gateway
>>     router with SNAT for bar. R3 is a Gateway router with no SNAT.
>>     Using 'alice1' as a client I was able to talk over TCP with
>>     'bar1' but connection with 'foo1' failed.
>>
>> 3. Regarding security and "leaking" of internal IPs. Reading through
>>    RFC 4787 [1], 5382 [2] and their update in 7857 [3], the
>>    specifications do not seem to mandate that SNAT implementations
>>    must filter incoming traffic destined directly to the internal
>>    network. Sections like "5. Filtering Behavior" in 4787 and
>>    "4.3 Externally Initiated Connections" in 5382 describe only
>>    behavior for traffic destined to external IP/Port associated
>>    with NAT on the device that performs NAT.
>>
>>    Besides, with the current implementation, it's already possible
>>    to scan the internal network with pings and TCP syn scanning.
>>
>> 4. We do have customers/clouds that depend on this functionality.
>>    This is a scenario that used to work in Openstack with ML2/OVS
>>    and migrating those clouds to ML2/OVN would break it.
>>
>> [0]
>> https://mail.openvswitch.org/pipermail/ovs-dev/2024-February/411670.html
>> [1]https://datatracker.ietf.org/doc/html/rfc4787
>> [2]https://datatracker.ietf.org/doc/html/rfc5382
>> [3]https://datatracker.ietf.org/doc/html/rfc7857
>>
>> Signed-off-by: Martin Kalcok <martin.kalcok@canonical.com>
>> ---
>>
> 
> Hi Martin,
> 
> I have just some nits down below.
> 
> 
>>  northd/northd.c         | 66 ++++++++++++++++++++++++++++-------
>>  northd/ovn-northd.8.xml | 29 ++++++++++++++++
>>  tests/ovn-northd.at     | 76 +++++++++++++++++++++++++++++++++++++----
>>  tests/system-ovn.at     | 68 ++++++++++++++++++++++++++++++++++++
>>  4 files changed, 220 insertions(+), 19 deletions(-)
>>
>> diff --git a/northd/northd.c b/northd/northd.c
>> index 02cf5b234..0726c8429 100644
>> --- a/northd/northd.c
>> +++ b/northd/northd.c
>> @@ -14413,20 +14413,27 @@ build_lrouter_out_is_dnat_local(struct
>> lflow_table *lflows,
>>
>>  static void
>>  build_lrouter_out_snat_match(struct lflow_table *lflows,
>> -                             const struct ovn_datapath *od,
>> -                             const struct nbrec_nat *nat, struct ds
>> *match,
>> -                             bool distributed_nat, int cidr_bits, bool
>> is_v6,
>> -                             struct ovn_port *l3dgw_port,
>> -                             struct lflow_ref *lflow_ref)
>> +                                         const struct ovn_datapath *od,
>> +                                         const struct nbrec_nat *nat,
>> +                                         struct ds *match,
>> +                                         bool distributed_nat, int
>> cidr_bits,
>> +                                         bool is_v6,
>> +                                         struct ovn_port *l3dgw_port,
>> +                                         struct lflow_ref *lflow_ref,
>> +                                         bool is_reverse)
>>  {
>>      ds_clear(match);
>>
>> -    ds_put_format(match, "ip && ip%c.src == %s", is_v6 ? '6' : '4',
>> +    ds_put_format(match, "ip && ip%c.%s == %s",
>> +                  is_v6 ? '6' : '4',
>> +                  is_reverse ? "dst" : "src",
>>                    nat->logical_ip);
>>
>>      if (!od->is_gw_router) {
>>          /* Distributed router. */
>> -        ds_put_format(match, " && outport == %s", l3dgw_port->json_key);
>> +        ds_put_format(match, " && %s == %s",
>> +                      is_reverse ? "inport" : "outport",
>> +                      l3dgw_port->json_key);
>>          if (od->n_l3dgw_ports) {
>>              ds_put_format(match, " && is_chassis_resident(\"%s\")",
>>                            distributed_nat
>> @@ -14437,7 +14444,7 @@ build_lrouter_out_snat_match(struct lflow_table
>> *lflows,
>>
>>      if (nat->allowed_ext_ips || nat->exempted_ext_ips) {
>>          lrouter_nat_add_ext_ip_match(od, lflows, match, nat,
>> -                                     is_v6, false, cidr_bits,
>> +                                     is_v6, is_reverse, cidr_bits,
>>                                       lflow_ref);
>>      }
>>  }
>> @@ -14464,7 +14471,8 @@ build_lrouter_out_snat_stateless_flow(struct
>> lflow_table *lflows,
>>      uint16_t priority = cidr_bits + 1;
>>
>>      build_lrouter_out_snat_match(lflows, od, nat, match, distributed_nat,
>> -                                 cidr_bits, is_v6, l3dgw_port, lflow_ref);
>> +                                 cidr_bits, is_v6, l3dgw_port, lflow_ref,
>> +                                 false);
>>
>>      if (!od->is_gw_router) {
>>          /* Distributed router. */
>> @@ -14511,7 +14519,7 @@ build_lrouter_out_snat_in_czone_flow(struct
>> lflow_table *lflows,
>>
>>      build_lrouter_out_snat_match(lflows, od, nat, match, distributed_nat,
>>                                   cidr_bits, is_v6, l3dgw_port,
>> -                                 lflow_ref);
>> +                                 lflow_ref, false);
>>
>>      if (od->n_l3dgw_ports) {
>>          priority += 128;
>> @@ -14560,7 +14568,8 @@ build_lrouter_out_snat_flow(struct lflow_table
>> *lflows,
>>                              struct ds *actions, bool distributed_nat,
>>                              struct eth_addr mac, int cidr_bits, bool
>> is_v6,
>>                              struct ovn_port *l3dgw_port,
>> -                            struct lflow_ref *lflow_ref)
>> +                            struct lflow_ref *lflow_ref,
>> +                            const struct chassis_features *features)
>>  {
>>      if (strcmp(nat->type, "snat") && strcmp(nat->type, "dnat_and_snat")) {
>>          return;
>> @@ -14574,7 +14583,9 @@ build_lrouter_out_snat_flow(struct lflow_table
>> *lflows,
>>      uint16_t priority = cidr_bits + 1;
>>
>>      build_lrouter_out_snat_match(lflows, od, nat, match, distributed_nat,
>> -                                 cidr_bits, is_v6, l3dgw_port, lflow_ref);
>> +                                 cidr_bits, is_v6, l3dgw_port, lflow_ref,
>> +                                 false);
>> +    size_t original_match_len = match->length;
>>
>>      if (!od->is_gw_router) {
>>          /* Distributed router. */
>> @@ -14599,6 +14610,35 @@ build_lrouter_out_snat_flow(struct lflow_table
>> *lflows,
>>                              priority, ds_cstr(match),
>>                              ds_cstr(actions), &nat->header_,
>>                              lflow_ref);
>> +
>> +    /* For the SNAT networks, we need to make sure that connections are
>> +     * properly tracked so we can decide whether to perform SNAT on
>> traffic
>> +     * exiting the network. */
>> +    if (features->ct_commit_to_zone && !strcmp(nat->type, "snat") &&
>> +        !od->is_gw_router) {
>> +        /* For traffic that comes from SNAT network, initiate CT state
>> before
>> +         * entering S_ROUTER_OUT_SNAT to allow matching on various CT
>> states.
>> +         */
>> +        ds_truncate(match, original_match_len);
>> +        ovn_lflow_add(lflows, od, S_ROUTER_OUT_POST_UNDNAT, 70,
>> +                      ds_cstr(match), "ct_snat; ",
>>
> 
> nit: Extra space after ct_snat;
> 
> 
>> +                      lflow_ref);
>> +
>> +        build_lrouter_out_snat_match(lflows, od, nat, match,
>> +                                     distributed_nat, cidr_bits, is_v6,
>> +                                     l3dgw_port, lflow_ref, true);
>> +
>> +        /* New traffic that goes into SNAT network is committed to CT to
>> avoid
>> +         * SNAT-ing replies.*/
>> +        ovn_lflow_add(lflows, od, S_ROUTER_OUT_SNAT, priority,
>> +                      ds_cstr(match), "ct_snat;",
>> +                      lflow_ref);
>> +
>> +        ds_put_cstr(match, " && ct.new");
>> +        ovn_lflow_add(lflows, od, S_ROUTER_OUT_POST_SNAT, priority,
>> +                      ds_cstr(match), "ct_commit_to_zone(snat); next; ",
>>
> 
> nit: Extra space after next;
> 
> 
>> +                      lflow_ref);
>> +    }
>>  }
>>
>>  static void
>> @@ -15137,7 +15177,7 @@ build_lrouter_nat_defrag_and_lb(
>>          } else {
>>              build_lrouter_out_snat_flow(lflows, od, nat, match, actions,
>>                                          distributed_nat, mac, cidr_bits,
>> is_v6,
>> -                                        l3dgw_port, lflow_ref);
>> +                                        l3dgw_port, lflow_ref, features);
>>          }
>>
>>          /* S_ROUTER_IN_ADMISSION - S_ROUTER_IN_IP_INPUT */
>> diff --git a/northd/ovn-northd.8.xml b/northd/ovn-northd.8.xml
>> index 90ce0de3f..93a0b781a 100644
>> --- a/northd/ovn-northd.8.xml
>> +++ b/northd/ovn-northd.8.xml
>> @@ -4876,6 +4876,13 @@ nd_ns {
>>
>>      <p>
>>        <ul>
>> +        <li>
>> +          A priority-70 logical flow is added that initiates CT state for
>> +          traffic that is configured to be SNATed on Distributed routers.
>> +          This allows the next table, <code>lr_out_snat</code>, to
>> +          effectively match on various CT states.
>> +        </li>
>> +
>>          <li>
>>            A priority-50 logical flow is added that commits any untracked
>> flows
>>            from the previous table <code>lr_out_undnat</code> for Gateway
>> @@ -5068,6 +5075,18 @@ nd_ns {
>>
>>        </li>
>>
>> +      <li>
>> +        An additional flow is added for traffic that goes in opposite
>> +        direction (i.e. it enters a network with configured SNAT). Where
>> the
>> +        flow above matched on <code>ip4.src == <var>A</var> &amp;&amp;
>> outport
>> +        == <var>GW</var></code>, this flow matches on <code> ip4.dst ==
>> +        <var>A</var> &amp;&amp; inport == <var>GW</var></code>. A CT
>> state is
>> +        initiated for this traffic so that the following table, <code>
>> +        lr_out_post_snat</code>, can identify whether the traffic flow was
>> +        initiated from the internal or external network.
>> +
>> +      </li>
>> +
>>        <li>
>>          A priority-0 logical flow with match <code>1</code> has actions
>>          <code>next;</code>.
>> @@ -5079,6 +5098,16 @@ nd_ns {
>>      <p>
>>        Packets reaching this table are processed according to the flows
>> below:
>>        <ul>
>> +        <li>
>> +          Traffic that goes directly into a network configured with SNAT
>> on
>> +          Distributed routers, and was initiated from an external network
>> (i.e.
>> +          it matches <code>ct.new</code>), is committed to the SNAT CT
>> zone.
>> +          This ensures that replies returning from the SNATed network do
>> not
>> +          have their source address translated. For details about match
>> rules
>> +          and priority see section "Egress Table 3: SNAT on Distributed
>> +          Routers".
>> +        </li>
>> +
>>          <li>
>>            A priority-0 logical flow that matches all packets not already
>>            handled (match <code>1</code>) and action <code>next;</code>.
>> diff --git a/tests/ovn-northd.at b/tests/ovn-northd.at
>> index be006fb32..3c9d9309b 100644
>> --- a/tests/ovn-northd.at
>> +++ b/tests/ovn-northd.at
>> @@ -1107,7 +1107,8 @@ ovn_start
>>  #
>>  # DR is connected to S1 and CR is connected to S2
>>
>> -check ovn-sbctl chassis-add gw1 geneve 127.0.0.1
>> +check ovn-sbctl chassis-add gw1 geneve 127.0.0.1 \
>> +  -- set chassis gw1 other_config:ct-commit-to-zone="true"
>>
>>  check ovn-nbctl lr-add DR
>>  check ovn-nbctl lrp-add DR DR-S1 02:ac:10:01:00:01 172.16.1.1/24
>> @@ -1155,15 +1156,24 @@ AT_CAPTURE_FILE([crflows])
>>  AT_CHECK([grep -e "lr_out_snat" drflows | ovn_strip_lflows], [0], [dnl
>>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
>> action=(next;)
>> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
>> 50.0.0.11 && inport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
>> ip4.src == $allowed_range), action=(ct_snat;)
>>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
>> 50.0.0.11 && outport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
>> ip4.dst == $allowed_range && (!ct.trk || !ct.rpl)),
>> action=(ct_snat(172.16.1.1);)
>>  ])
>>
>> +AT_CHECK([grep -e "lr_out_post_snat" drflows | ovn_strip_lflows], [0],
>> [dnl
>> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
>> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
>> 50.0.0.11 && inport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
>> ip4.src == $allowed_range && ct.new), action=(ct_commit_to_zone(snat);
>> next; )
>> +])
>> +
>>  AT_CHECK([grep -e "lr_out_snat" crflows | ovn_strip_lflows], [0], [dnl
>>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
>> action=(next;)
>>    table=??(lr_out_snat        ), priority=33   , match=(ip && ip4.src ==
>> 50.0.0.11 && ip4.dst == $allowed_range && (!ct.trk || !ct.rpl)),
>> action=(ct_snat(172.16.1.1);)
>>  ])
>>
>> +AT_CHECK([grep -e "lr_out_post_snat" crflows | ovn_strip_lflows], [0],
>> [dnl
>> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
>> +])
>>
>>  # SNAT with DISALLOWED_IPs
>>  check ovn-nbctl lr-nat-del DR snat  50.0.0.11
>> @@ -1185,10 +1195,16 @@ AT_CAPTURE_FILE([crflows2])
>>  AT_CHECK([grep -e "lr_out_snat" drflows2 | ovn_strip_lflows], [0], [dnl
>>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
>> action=(next;)
>> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
>> 50.0.0.11 && inport == "DR-S1" && is_chassis_resident("cr-DR-S1")),
>> action=(ct_snat;)
>>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
>> 50.0.0.11 && outport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
>> (!ct.trk || !ct.rpl)), action=(ct_snat(172.16.1.1);)
>>    table=??(lr_out_snat        ), priority=163  , match=(ip && ip4.src ==
>> 50.0.0.11 && outport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
>> ip4.dst == $disallowed_range), action=(next;)
>>  ])
>>
>> +AT_CHECK([grep -e "lr_out_post_snat" drflows2 | ovn_strip_lflows], [0],
>> [dnl
>> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
>> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
>> 50.0.0.11 && inport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
>> ct.new), action=(ct_commit_to_zone(snat); next; )
>> +])
>> +
>>  AT_CHECK([grep -e "lr_out_snat" crflows2 | ovn_strip_lflows], [0], [dnl
>>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
>> action=(next;)
>> @@ -1196,6 +1212,10 @@ AT_CHECK([grep -e "lr_out_snat" crflows2 |
>> ovn_strip_lflows], [0], [dnl
>>    table=??(lr_out_snat        ), priority=35   , match=(ip && ip4.src ==
>> 50.0.0.11 && ip4.dst == $disallowed_range), action=(next;)
>>  ])
>>
>> +AT_CHECK([grep -e "lr_out_post_snat" crflows2 | ovn_strip_lflows], [0],
>> [dnl
>> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
>> +])
>> +
>>  # Stateful FIP with ALLOWED_IPs
>>  check ovn-nbctl lr-nat-del DR snat  50.0.0.11
>>  check ovn-nbctl lr-nat-del CR snat  50.0.0.11
>> @@ -1217,12 +1237,20 @@ AT_CHECK([grep -e "lr_out_snat" drflows3 |
>> ovn_strip_lflows], [0], [dnl
>>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
>> 50.0.0.11 && outport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
>> ip4.dst == $allowed_range && (!ct.trk || !ct.rpl)),
>> action=(ct_snat(172.16.1.2);)
>>  ])
>>
>> +AT_CHECK([grep -e "lr_out_post_snat" drflows3 | ovn_strip_lflows], [0],
>> [dnl
>> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
>> +])
>> +
>>  AT_CHECK([grep -e "lr_out_snat" crflows3 | ovn_strip_lflows], [0], [dnl
>>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
>> action=(next;)
>>    table=??(lr_out_snat        ), priority=33   , match=(ip && ip4.src ==
>> 50.0.0.11 && ip4.dst == $allowed_range && (!ct.trk || !ct.rpl)),
>> action=(ct_snat(172.16.1.2);)
>>  ])
>>
>> +AT_CHECK([grep -e "lr_out_post_snat" crflows3 | ovn_strip_lflows], [0],
>> [dnl
>> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
>> +])
>> +
>>  # Stateful FIP with DISALLOWED_IPs
>>  ovn-nbctl lr-nat-del DR dnat_and_snat  172.16.1.2
>>  ovn-nbctl lr-nat-del CR dnat_and_snat  172.16.1.2
>> @@ -1279,7 +1307,7 @@ AT_CHECK([grep -e "lr_out_snat" crflows5 |
>> ovn_strip_lflows], [0], [dnl
>>    table=??(lr_out_snat        ), priority=33   , match=(ip && ip4.src ==
>> 50.0.0.11 && ip4.dst == $allowed_range), action=(ip4.src=172.16.1.2; next;)
>>  ])
>>
>> -# Stateful FIP with DISALLOWED_IPs
>> +# Stateless FIP with DISALLOWED_IPs
>>  ovn-nbctl lr-nat-del DR dnat_and_snat  172.16.1.2
>>  ovn-nbctl lr-nat-del CR dnat_and_snat  172.16.1.2
>>
>> @@ -5521,7 +5549,8 @@ AT_CHECK([grep "lr_out_snat" lr0flows |
>> ovn_strip_lflows], [0], [dnl
>>
>>  check ovn-sbctl chassis-add gw1 geneve 127.0.0.1 \
>>    -- set chassis gw1 other_config:ct-no-masked-label="true" \
>> -  -- set chassis gw1 other_config:ovn-ct-lb-related="true"
>> +  -- set chassis gw1 other_config:ovn-ct-lb-related="true" \
>> +  -- set chassis gw1 other_config:ct-commit-to-zone="true"
>>
>>  # Create a distributed gw port on lr0
>>  check ovn-nbctl ls-add public
>> @@ -5622,16 +5651,26 @@ AT_CHECK([grep "lr_out_undnat" lr0flows |
>> ovn_strip_lflows], [0], [dnl
>>
>>  AT_CHECK([grep "lr_out_post_undnat" lr0flows | ovn_strip_lflows], [0],
>> [dnl
>>    table=??(lr_out_post_undnat ), priority=0    , match=(1), action=(next;)
>> +  table=??(lr_out_post_undnat ), priority=70   , match=(ip && ip4.src ==
>> 10.0.0.0/24 && outport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public")), action=(ct_snat; )
>> +  table=??(lr_out_post_undnat ), priority=70   , match=(ip && ip4.src ==
>> 10.0.0.10 && outport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public")), action=(ct_snat; )
>>  ])
>>
>>  AT_CHECK([grep "lr_out_snat" lr0flows | ovn_strip_lflows], [0], [dnl
>>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
>> action=(next;)
>> +  table=??(lr_out_snat        ), priority=153  , match=(ip && ip4.dst ==
>> 10.0.0.0/24 && inport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public")), action=(ct_snat;)
>>    table=??(lr_out_snat        ), priority=153  , match=(ip && ip4.src ==
>> 10.0.0.0/24 && outport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public") && (!ct.trk || !ct.rpl)),
>> action=(ct_snat(172.168.0.10);)
>> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
>> 10.0.0.10 && inport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public")), action=(ct_snat;)
>>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
>> 10.0.0.10 && outport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public") && (!ct.trk || !ct.rpl)),
>> action=(ct_snat(172.168.0.30);)
>>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
>> 10.0.0.3 && outport == "lr0-public" && is_chassis_resident("cr-lr0-public")
>> && (!ct.trk || !ct.rpl)), action=(ct_snat(172.168.0.20);)
>>  ])
>>
>> +AT_CHECK([grep "lr_out_post_snat" lr0flows | ovn_strip_lflows], [0], [dnl
>> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
>> +  table=??(lr_out_post_snat   ), priority=153  , match=(ip && ip4.dst ==
>> 10.0.0.0/24 && inport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public") && ct.new),
>> action=(ct_commit_to_zone(snat); next; )
>> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
>> 10.0.0.10 && inport == "lr0-public" && is_chassis_resident("cr-lr0-public")
>> && ct.new), action=(ct_commit_to_zone(snat); next; )
>> +])
>> +
>>  # Associate load balancer to lr0
>>
>>  check ovn-nbctl lb-add lb0 172.168.0.100:8082 "10.0.0.50:82,10.0.0.60:82"
>> @@ -5770,16 +5809,26 @@ AT_CHECK([grep "lr_out_undnat" lr0flows |
>> ovn_strip_lflows], [0], [dnl
>>
>>  AT_CHECK([grep "lr_out_post_undnat" lr0flows | ovn_strip_lflows], [0],
>> [dnl
>>    table=??(lr_out_post_undnat ), priority=0    , match=(1), action=(next;)
>> +  table=??(lr_out_post_undnat ), priority=70   , match=(ip && ip4.src ==
>> 10.0.0.0/24 && outport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public")), action=(ct_snat; )
>> +  table=??(lr_out_post_undnat ), priority=70   , match=(ip && ip4.src ==
>> 10.0.0.10 && outport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public")), action=(ct_snat; )
>>  ])
>>
>>  AT_CHECK([grep "lr_out_snat" lr0flows | ovn_strip_lflows], [0], [dnl
>>    table=??(lr_out_snat        ), priority=0    , match=(1), action=(next;)
>>    table=??(lr_out_snat        ), priority=120  , match=(nd_ns),
>> action=(next;)
>> +  table=??(lr_out_snat        ), priority=153  , match=(ip && ip4.dst ==
>> 10.0.0.0/24 && inport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public")), action=(ct_snat;)
>>    table=??(lr_out_snat        ), priority=153  , match=(ip && ip4.src ==
>> 10.0.0.0/24 && outport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public") && (!ct.trk || !ct.rpl)),
>> action=(ct_snat(172.168.0.10);)
>> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
>> 10.0.0.10 && inport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public")), action=(ct_snat;)
>>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
>> 10.0.0.10 && outport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public") && (!ct.trk || !ct.rpl)),
>> action=(ct_snat(172.168.0.30);)
>>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
>> 10.0.0.3 && outport == "lr0-public" && is_chassis_resident("cr-lr0-public")
>> && (!ct.trk || !ct.rpl)), action=(ct_snat(172.168.0.20);)
>>  ])
>>
>> +AT_CHECK([grep "lr_out_post_snat" lr0flows | ovn_strip_lflows], [0], [dnl
>> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
>> +  table=??(lr_out_post_snat   ), priority=153  , match=(ip && ip4.dst ==
>> 10.0.0.0/24 && inport == "lr0-public" &&
>> is_chassis_resident("cr-lr0-public") && ct.new),
>> action=(ct_commit_to_zone(snat); next; )
>> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
>> 10.0.0.10 && inport == "lr0-public" && is_chassis_resident("cr-lr0-public")
>> && ct.new), action=(ct_commit_to_zone(snat); next; )
>> +])
>> +
>>  # Make the logical router as Gateway router
>>  check ovn-nbctl clear logical_router_port lr0-public gateway_chassis
>>  check ovn-nbctl set logical_router lr0 options:chassis=gw1
>> @@ -7606,9 +7655,14 @@ ovn_start
>>  # Validate SNAT, DNAT and DNAT_AND_SNAT behavior with multiple
>>  # distributed gateway LRPs.
>>
>> -check ovn-sbctl chassis-add gw1 geneve 127.0.0.1
>> -check ovn-sbctl chassis-add gw2 geneve 128.0.0.1
>> -check ovn-sbctl chassis-add gw3 geneve 129.0.0.1
>> +check ovn-sbctl chassis-add gw1 geneve 127.0.0.1 \
>> +  -- set chassis gw1 other_config:ct-commit-to-zone="true"
>> +
>> +check ovn-sbctl chassis-add gw2 geneve 128.0.0.1 \
>> +  -- set chassis gw2 other_config:ct-commit-to-zone="true"
>> +
>> +check ovn-sbctl chassis-add gw3 geneve 129.0.0.1 \
>> +  -- set chassis gw3 other_config:ct-commit-to-zone="true"
>>
>>  check ovn-nbctl lr-add DR
>>  check ovn-nbctl lrp-add DR DR-S1 02:ac:10:01:00:01 172.16.1.1/24
>> @@ -7673,11 +7727,21 @@ AT_CHECK([grep lr_in_unsnat lrflows | grep ct_snat
>> | ovn_strip_lflows], [0], [dn
>>  ])
>>
>>  AT_CHECK([grep lr_out_snat lrflows | grep ct_snat | ovn_strip_lflows],
>> [0], [dnl
>> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
>> 20.0.0.10 && inport == "DR-S1" && is_chassis_resident("cr-DR-S1")),
>> action=(ct_snat;)
>> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
>> 20.0.0.10 && inport == "DR-S2" && is_chassis_resident("cr-DR-S2")),
>> action=(ct_snat;)
>> +  table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.dst ==
>> 20.0.0.10 && inport == "DR-S3" && is_chassis_resident("cr-DR-S3")),
>> action=(ct_snat;)
>>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
>> 20.0.0.10 && outport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
>> (!ct.trk || !ct.rpl)), action=(ct_snat(172.16.1.10);)
>>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
>> 20.0.0.10 && outport == "DR-S2" && is_chassis_resident("cr-DR-S2") &&
>> (!ct.trk || !ct.rpl)), action=(ct_snat(10.0.0.10);)
>>    table=??(lr_out_snat        ), priority=161  , match=(ip && ip4.src ==
>> 20.0.0.10 && outport == "DR-S3" && is_chassis_resident("cr-DR-S3") &&
>> (!ct.trk || !ct.rpl)), action=(ct_snat(192.168.0.10);)
>>  ])
>>
>> +AT_CHECK([grep lr_out_post_snat lrflows | ovn_strip_lflows], [0], [dnl
>> +  table=??(lr_out_post_snat   ), priority=0    , match=(1), action=(next;)
>> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
>> 20.0.0.10 && inport == "DR-S1" && is_chassis_resident("cr-DR-S1") &&
>> ct.new), action=(ct_commit_to_zone(snat); next; )
>> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
>> 20.0.0.10 && inport == "DR-S2" && is_chassis_resident("cr-DR-S2") &&
>> ct.new), action=(ct_commit_to_zone(snat); next; )
>> +  table=??(lr_out_post_snat   ), priority=161  , match=(ip && ip4.dst ==
>> 20.0.0.10 && inport == "DR-S3" && is_chassis_resident("cr-DR-S3") &&
>> ct.new), action=(ct_commit_to_zone(snat); next; )
>> +])
>> +
>>  check ovn-nbctl --wait=sb lr-nat-del DR snat 20.0.0.10
>>  AT_CHECK([ovn-sbctl dump-flows DR | grep -e lr_in_unsnat -e lr_out_snat |
>> grep ct_snat | wc -l], [0], [0
>>  ])
>> diff --git a/tests/system-ovn.at b/tests/system-ovn.at
>> index c699f7960..68adfa4e6 100644
>> --- a/tests/system-ovn.at
>> +++ b/tests/system-ovn.at
>> @@ -3574,6 +3574,39 @@ NS_CHECK_EXEC([foo1], [ping -q -c 3 -i 0.3 -w 2
>> 10.0.0.1 | FORMAT_PING], \
>>  3 packets transmitted, 3 received, 0% packet loss, time 0ms
>>  ])
>>
>> +# test_connectivity_from_ext takes parameters 'vm' and 'ip'. It tests
>> +# icmp, udp and tcp connectivity from external network to the 'vm' on
>> +# the specified 'ip'.
>> +test_connectivity_from_ext() {
>> +    local vm=$1; shift
>> +    local ip=$1; shift
>> +
>> +    # Start listening daemons for UDP and TCP connections
>> +    NETNS_DAEMONIZE($vm, [nc -l -u 1234], [nc-$vm-$ip-udp.pid])
>> +    NETNS_DAEMONIZE($vm, [nc -l -k 1235], [nc-$vm-$ip-tcp.pid])
>> +
>> +    # Ensure that vm can be pinged on the specified IP
>> +    NS_CHECK_EXEC([alice1], [ping -q -c 3 -i 0.3 -w 2 $ip | FORMAT_PING],
>> \
>> +    [0], [dnl
>> +3 packets transmitted, 3 received, 0% packet loss, time 0ms
>> +])
>> +
>> +    # Perform two consecutive UDP connections to the specified IP
>> +    NS_CHECK_EXEC([alice1], [nc -u $ip 1234 -p 2000 -z])
>> +    NS_CHECK_EXEC([alice1], [nc -u $ip 1234 -p 2000 -z])
>> +
>> +    # Send data over TCP connection to the specified IP
>> +    NS_CHECK_EXEC([alice1], [echo "TCP test" | nc --send-only $ip 1235])
>> +}
>> +
>> +# Test access from external network to the internal IP of a VM that
>> +# has also configured DNAT
>> +test_connectivity_from_ext foo1 192.168.1.2
>> +
>> +# Test access from external network to the internal IP of a VM that
>> +# does not have DNAT
>> +test_connectivity_from_ext bar1 192.168.2.2
>> +
>>  OVS_WAIT_UNTIL([
>>      total_pkts=$(cat ext-net.tcpdump | wc -l)
>>      test "${total_pkts}" = "3"
>> @@ -3740,6 +3773,39 @@ sed -e 's/zone=[[0-9]]*/zone=<cleared>/'], [0], [dnl
>>
>>  icmpv6,orig=(src=fd12::2,dst=fd20::2,id=<cleared>,type=128,code=0),reply=(src=fd20::2,dst=fd20::1,id=<cleared>,type=129,code=0),zone=<cleared>
>>  ])
>>
>> +# test_connectivity_from_ext takes parameters 'vm' and 'ip'. It tests
>> +# icmp, udp and tcp connectivity from external network to the 'vm' on
>> +# the specified 'ip'.
>> +test_connectivity_from_ext() {
>> +    local vm=$1; shift
>> +    local ip=$1; shift
>> +
>> +    # Start listening daemons for UDP and TCP connections
>> +    NETNS_DAEMONIZE($vm, [nc -l -u 1234], [nc-$vm-$ip-udp.pid])
>> +    NETNS_DAEMONIZE($vm, [nc -l -k 1235], [nc-$vm-$ip-tcp.pid])
>> +
>> +    # Ensure that vm can be pinged on the specified IP
>> +    NS_CHECK_EXEC([alice1], [ping -q -c 3 -i 0.3 -w 2 $ip | FORMAT_PING],
>> \
>> +    [0], [dnl
>> +3 packets transmitted, 3 received, 0% packet loss, time 0ms
>> +])
>> +
>> +    # Perform two consecutive UDP connections to the specified IP
>> +    NS_CHECK_EXEC([alice1], [nc -u $ip 1234 -p 2000 -z])
>> +    NS_CHECK_EXEC([alice1], [nc -u $ip 1234 -p 2000 -z])
>> +
>> +    # Send data over TCP connection to the specified IP
>> +    NS_CHECK_EXEC([alice1], [echo "TCP test" | nc --send-only $ip 1235])
>> +}
>> +
>> +# Test access from external network to the internal IP of a VM that
>> +# has also configured DNAT
>> +test_connectivity_from_ext foo1 fd11::2
>> +
>> +# Test access from external network to the internal IP of a VM that
>> +# does not have DNAT
>> +test_connectivity_from_ext bar1 fd12::2
>> +
>>  OVS_APP_EXIT_AND_WAIT([ovn-controller])
>>
>>  as ovn-sb
>> @@ -3920,6 +3986,7 @@ NS_CHECK_EXEC([foo2], [ping -q -c 3 -i 0.3 -w 2
>> 172.16.1.4 | FORMAT_PING], \
>>  AT_CHECK([ovs-appctl dpctl/dump-conntrack | grep icmp |
>> FORMAT_CT(172.16.1.1) | \
>>  sed -e 's/zone=[[0-9]]*/zone=<cleared>/'], [0], [dnl
>>
>>  icmp,orig=(src=172.16.1.1,dst=172.16.1.4,id=<cleared>,type=8,code=0),reply=(src=192.168.2.2,dst=172.16.1.1,id=<cleared>,type=0,code=0),zone=<cleared>
>>
>> +icmp,orig=(src=172.16.1.1,dst=192.168.2.2,id=<cleared>,type=8,code=0),reply=(src=192.168.2.2,dst=172.16.1.1,id=<cleared>,type=0,code=0),zone=<cleared>
>>
>>  icmp,orig=(src=192.168.1.3,dst=172.16.1.4,id=<cleared>,type=8,code=0),reply=(src=172.16.1.4,dst=172.16.1.1,id=<cleared>,type=0,code=0),zone=<cleared>
>>  ])
>>
>> @@ -4088,6 +4155,7 @@ NS_CHECK_EXEC([foo2], [ping -q -c 3 -i 0.3 -w 2
>> fd20::4 | FORMAT_PING], \
>>  AT_CHECK([ovs-appctl dpctl/dump-conntrack | FORMAT_CT(fd20::1) | \
>>  sed -e 's/zone=[[0-9]]*/zone=<cleared>/'], [0], [dnl
>>
>>  icmpv6,orig=(src=fd11::3,dst=fd20::4,id=<cleared>,type=128,code=0),reply=(src=fd20::4,dst=fd20::1,id=<cleared>,type=129,code=0),zone=<cleared>
>>
>> +icmpv6,orig=(src=fd20::1,dst=fd12::2,id=<cleared>,type=128,code=0),reply=(src=fd12::2,dst=fd20::1,id=<cleared>,type=129,code=0),zone=<cleared>
>>
>>  icmpv6,orig=(src=fd20::1,dst=fd20::4,id=<cleared>,type=128,code=0),reply=(src=fd12::2,dst=fd20::1,id=<cleared>,type=129,code=0),zone=<cleared>
>>  ])
>>
>> --
>> 2.40.1
>>
>>
> Other than that it looks good.
> 

Same here.

Thanks,
Dumitru