diff mbox series

[ovs-dev,3/3] northd: Explicitly handle SNAT for ICMP need frag

Message ID 20231206101951.93483-4-amusil@redhat.com
State Changes Requested
Headers show
Series Keep track of SNAT status for ICMP need frag | expand

Checks

Context Check Description
ovsrobot/apply-robot success apply and check: success
ovsrobot/github-robot-_Build_and_Test success github build: passed
ovsrobot/github-robot-_ovn-kubernetes success github build: passed

Commit Message

Ales Musil Dec. 6, 2023, 10:19 a.m. UTC 
Considering following topology:
client - sw0 - lrp0 - lr - lrp1 - sw1 - server
sw0 in subnet 192.168.0.0/24
sw1 in subnet 172.168.0.0/24
SNAT configured for client
gateway_mtu=1400 configured for lrp0

If we send UDP traffic from client to server
and server responds with packet bigger than 1400
the following sequence will happen:

1) Packet is coming into lr via lrp1
2) unSNAT
3) Routing, the outport will be set to lrp0
4) Check for packet larger will fail
5) We will generate ICMP need frag

However, the last step is wrong from the server
perspective. The ICMP message will have IP source
address = lrp1 IP address. Which means that SNAT won't
happen because the source is not within the sw0 subnet,
but the inner packet has sw0 subnet address, because it
was unSNATted. This results in server ignoring the ICMP
message because server never sent any packet to the
sw0 subnet.

In order to prevent this issue perform SNAT for the
ICMP packet. Because the packet is related to already
existing connection we just need to perform
ct_commit_nat(snat) action.

This is achieved with addition of the following flow for
"lr_in_larger_pkts" stage (the flow for IPv6 is the in
regard to the addition):

match=(inport == "INPORT" && outport == "OUTPORT" && ip4 && REGBIT_PKT_LARGER && REGBIT_EGRESS_LOOPBACK == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; REGBIT_EGRESS_LOOPBACK = 1; REGBIT_PKT_LARGER = 0; eth.dst = ETH_DST; ip4.dst = ip4.src; ip4.src = IP_SRC; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)

Also, add flow to "lr_out_post_snat" stage:

match=(icmp && flags.icmp_snat == 1), action=(ct_commit_nat(snat);)

Partially revert 0e49f49c73d6 ("northd: Allow need frag to be SNATed")
which attempted to fix the same issue in a wrong way.

Fixes: 0e49f49c73d6 ("northd: Allow need frag to be SNATed")
Reported-at: https://issues.redhat.com/browse/FDP-134
Reported-at: https://issues.redhat.com/browse/FDP-159
Signed-off-by: Ales Musil <amusil@redhat.com>
---
 include/ovn/logical-fields.h |   1 +
 lib/logical-fields.c         |   4 +
 northd/northd.c              | 182 +++++++++++++++++++----------------
 tests/ovn-northd.at          | 118 ++++++++++++++++-------
 tests/ovn.at                 |   6 +-
 tests/system-ovn-kmod.at     |   3 +-
 6 files changed, 192 insertions(+), 122 deletions(-)
diff mbox series

Patch

diff --git a/include/ovn/logical-fields.h b/include/ovn/logical-fields.h
index 272277ec4..497a25247 100644
--- a/include/ovn/logical-fields.h
+++ b/include/ovn/logical-fields.h
@@ -78,6 +78,7 @@  enum mff_log_flags_bits {
     MLF_LOOKUP_COMMIT_ECMP_NH_BIT = 13,
     MLF_USE_LB_AFF_SESSION_BIT = 14,
     MLF_LOCALNET_BIT = 15,
+    MLF_ICMP_SNAT = 16,
 };
 
 /* MFF_LOG_FLAGS_REG flag assignments */
diff --git a/lib/logical-fields.c b/lib/logical-fields.c
index 7a1e66d0a..65106050a 100644
--- a/lib/logical-fields.c
+++ b/lib/logical-fields.c
@@ -132,6 +132,10 @@  ovn_init_symtab(struct shash *symtab)
     snprintf(flags_str, sizeof flags_str, "flags[%d]",
              MLF_LOCALNET_BIT);
     expr_symtab_add_subfield(symtab, "flags.localnet", NULL,
+                            flags_str);
+    snprintf(flags_str, sizeof flags_str, "flags[%d]",
+             MLF_ICMP_SNAT);
+    expr_symtab_add_subfield(symtab, "flags.icmp_snat", NULL,
                              flags_str);
 
     /* Connection tracking state. */
diff --git a/northd/northd.c b/northd/northd.c
index 35d9b11d3..5776c8207 100644
--- a/northd/northd.c
+++ b/northd/northd.c
@@ -13991,96 +13991,103 @@  build_arp_resolve_flows_for_lsp(
     }
 }
 
+#define ICMP4_NEED_FRAG_FORMAT                           \
+    "icmp4_error {"                                      \
+    "%s"                                                 \
+    REGBIT_EGRESS_LOOPBACK" = 1; "                       \
+    REGBIT_PKT_LARGER" = 0; "                            \
+    "eth.dst = %s; "                                     \
+    "ip4.dst = ip4.src; "                                \
+    "ip4.src = %s; "                                     \
+    "ip.ttl = 255; "                                     \
+    "icmp4.type = 3; /* Destination Unreachable. */ "    \
+    "icmp4.code = 4; /* Frag Needed and DF was Set. */ " \
+    "icmp4.frag_mtu = %d; "                              \
+    "next(pipeline=ingress, table=%d); };"               \
+
+#define ICMP6_NEED_FRAG_FORMAT               \
+    "icmp6_error {"                          \
+    "%s"                                     \
+    REGBIT_EGRESS_LOOPBACK" = 1; "           \
+    REGBIT_PKT_LARGER" = 0; "                \
+    "eth.dst = %s; "                         \
+    "ip6.dst = ip6.src; "                    \
+    "ip6.src = %s; "                         \
+    "ip.ttl = 255; "                         \
+    "icmp6.type = 2; /* Packet Too Big. */ " \
+    "icmp6.code = 0; "                       \
+    "icmp6.frag_mtu = %d; "                  \
+    "next(pipeline=ingress, table=%d); };"
+
 static void
-build_icmperr_pkt_big_flows(struct ovn_port *op, int mtu, struct hmap *lflows,
-                            const struct shash *meter_groups, struct ds *match,
-                            struct ds *actions, enum ovn_stage stage,
-                            struct ovn_port *outport)
-{
-    char *outport_match = outport ? xasprintf("outport == %s && ",
-                                              outport->json_key)
-                                  : NULL;
+create_icmp_need_frag_lflow(const struct ovn_port *op, int mtu,
+                            struct ds *actions, struct ds *match,
+                            const char *meter, struct hmap *lflows,
+                            enum ovn_stage stage, uint16_t priority,
+                            bool is_ipv6, const char *extra_match,
+                            const char *extra_action)
+{
+    if ((is_ipv6 && !op->lrp_networks.ipv6_addrs) ||
+        (!is_ipv6 && !op->lrp_networks.ipv4_addrs)) {
+        return;
+    }
+
+    const char *ip = is_ipv6
+                     ? op->lrp_networks.ipv6_addrs[0].addr_s
+                     : op->lrp_networks.ipv4_addrs[0].addr_s;
+    size_t match_len = match->length;
 
-    char *ip4_src = NULL;
+    ds_put_format(match, " && ip%c && "REGBIT_PKT_LARGER
+                  " && "REGBIT_EGRESS_LOOPBACK" == 0", is_ipv6 ? '6' : '4');
 
-    if (outport && outport->lrp_networks.ipv4_addrs) {
-        ip4_src = outport->lrp_networks.ipv4_addrs[0].addr_s;
-    } else if (op->lrp_networks.ipv4_addrs) {
-        ip4_src = op->lrp_networks.ipv4_addrs[0].addr_s;
+    if (*extra_match) {
+        ds_put_format(match, " && %s", extra_match);
     }
 
-    if (ip4_src) {
-        ds_clear(match);
-        ds_put_format(match, "inport == %s && %sip4 && "REGBIT_PKT_LARGER
-                      " && "REGBIT_EGRESS_LOOPBACK" == 0", op->json_key,
-                      outport ? outport_match : "");
+    ds_clear(actions);
+    ds_put_format(actions,
+                  is_ipv6 ? ICMP6_NEED_FRAG_FORMAT : ICMP4_NEED_FRAG_FORMAT,
+                  extra_action, op->lrp_networks.ea_s, ip,
+                  mtu, ovn_stage_get_table(S_ROUTER_IN_ADMISSION));
 
-        ds_clear(actions);
-        /* Set icmp4.frag_mtu to gw_mtu */
-        ds_put_format(actions,
-            "icmp4_error {"
-            REGBIT_EGRESS_LOOPBACK" = 1; "
-            REGBIT_PKT_LARGER" = 0; "
-            "eth.dst = %s; "
-            "ip4.dst = ip4.src; "
-            "ip4.src = %s; "
-            "ip.ttl = 255; "
-            "icmp4.type = 3; /* Destination Unreachable. */ "
-            "icmp4.code = 4; /* Frag Needed and DF was Set. */ "
-            "icmp4.frag_mtu = %d; "
-            "next(pipeline=ingress, table=%d); };",
-            op->lrp_networks.ea_s, ip4_src, mtu,
-            ovn_stage_get_table(S_ROUTER_IN_ADMISSION));
-        ovn_lflow_add_with_hint__(lflows, op->od, stage, 150,
-                                  ds_cstr(match), ds_cstr(actions),
-                                  NULL,
-                                  copp_meter_get(
-                                        COPP_ICMP4_ERR,
-                                        op->od->nbr->copp,
-                                        meter_groups),
-                                  &op->nbrp->header_);
-    }
+    ovn_lflow_add_with_hint__(lflows, op->od, stage, priority,
+                              ds_cstr(match), ds_cstr(actions),
+                              NULL, meter, &op->nbrp->header_);
 
-    char *ip6_src = NULL;
+    ds_truncate(match, match_len);
+}
 
-    if (outport && outport->lrp_networks.ipv6_addrs) {
-        ip6_src = outport->lrp_networks.ipv6_addrs[0].addr_s;
-    } else if (op->lrp_networks.ipv6_addrs) {
-        ip6_src = op->lrp_networks.ipv6_addrs[0].addr_s;
-    }
+static void
+build_icmperr_pkt_big_flows(struct ovn_port *op, int mtu, struct hmap *lflows,
+                            const struct shash *meter_groups, struct ds *match,
+                            struct ds *actions, enum ovn_stage stage,
+                            struct ovn_port *outport)
+{
+    const char *ipv4_meter = copp_meter_get(COPP_ICMP4_ERR, op->od->nbr->copp,
+                                            meter_groups);
+    const char *ipv6_meter = copp_meter_get(COPP_ICMP6_ERR, op->od->nbr->copp,
+                                            meter_groups);
 
-    if (ip6_src) {
-        ds_clear(match);
-        ds_put_format(match, "inport == %s && %sip6 && "REGBIT_PKT_LARGER
-                      " && "REGBIT_EGRESS_LOOPBACK" == 0", op->json_key,
-                      outport ? outport_match : "");
+    ds_clear(match);
+    ds_put_format(match, "inport == %s", op->json_key);
 
-        ds_clear(actions);
-        /* Set icmp6.frag_mtu to gw_mtu */
-        ds_put_format(actions,
-            "icmp6_error {"
-            REGBIT_EGRESS_LOOPBACK" = 1; "
-            REGBIT_PKT_LARGER" = 0; "
-            "eth.dst = %s; "
-            "ip6.dst = ip6.src; "
-            "ip6.src = %s; "
-            "ip.ttl = 255; "
-            "icmp6.type = 2; /* Packet Too Big. */ "
-            "icmp6.code = 0; "
-            "icmp6.frag_mtu = %d; "
-            "next(pipeline=ingress, table=%d); };",
-            op->lrp_networks.ea_s, ip6_src, mtu,
-            ovn_stage_get_table(S_ROUTER_IN_ADMISSION));
-        ovn_lflow_add_with_hint__(lflows, op->od, stage, 150,
-                                  ds_cstr(match), ds_cstr(actions),
-                                  NULL,
-                                  copp_meter_get(
-                                        COPP_ICMP6_ERR,
-                                        op->od->nbr->copp,
-                                        meter_groups),
-                                  &op->nbrp->header_);
+    if (outport) {
+        ds_put_format(match, " && outport == %s", outport->json_key);
+
+        create_icmp_need_frag_lflow(op, mtu, actions, match, ipv4_meter,
+                                    lflows, stage, 160, false,
+                                    "ct.trk && ct.rpl && ct.dnat",
+                                    "flags.icmp_snat = 1; ");
+        create_icmp_need_frag_lflow(op, mtu, actions, match, ipv6_meter,
+                                    lflows, stage, 160, true,
+                                    "ct.trk && ct.rpl && ct.dnat",
+                                    "flags.icmp_snat = 1; ");
     }
-    free(outport_match);
+
+    create_icmp_need_frag_lflow(op, mtu, actions, match, ipv4_meter, lflows,
+                                stage, 150, false, "", "");
+    create_icmp_need_frag_lflow(op, mtu, actions, match, ipv6_meter, lflows,
+                                stage, 150, true, "", "");
 }
 
 static void
@@ -14088,8 +14095,8 @@  build_check_pkt_len_flows_for_lrp(struct ovn_port *op,
                                   struct hmap *lflows,
                                   const struct hmap *lr_ports,
                                   const struct shash *meter_groups,
-                                  struct ds *match,
-                                  struct ds *actions)
+                                  struct ds *match, struct ds *actions,
+                                  const struct chassis_features *features)
 {
     int gw_mtu = smap_get_int(&op->nbrp->options, "gateway_mtu", 0);
     if (gw_mtu <= 0) {
@@ -14118,6 +14125,12 @@  build_check_pkt_len_flows_for_lrp(struct ovn_port *op,
                                     match, actions, S_ROUTER_IN_LARGER_PKTS,
                                     op);
     }
+
+    if (features->ct_commit_nat_v2) {
+        ovn_lflow_add_with_hint(lflows, op->od, S_ROUTER_OUT_POST_SNAT, 100,
+                                "icmp && flags.icmp_snat == 1",
+                                "ct_commit_nat(snat);", &op->nbrp->header_);
+    }
 }
 
 /* Local router ingress table CHK_PKT_LEN: Check packet length.
@@ -14138,7 +14151,8 @@  build_check_pkt_len_flows_for_lrouter(
         struct ovn_datapath *od, struct hmap *lflows,
         const struct hmap *lr_ports,
         struct ds *match, struct ds *actions,
-        const struct shash *meter_groups)
+        const struct shash *meter_groups,
+        const struct chassis_features *features)
 {
     ovs_assert(od->nbr);
 
@@ -14155,7 +14169,7 @@  build_check_pkt_len_flows_for_lrouter(
             continue;
         }
         build_check_pkt_len_flows_for_lrp(rp, lflows, lr_ports, meter_groups,
-                                          match, actions);
+                                          match, actions, features);
     }
 }
 
@@ -16125,7 +16139,7 @@  build_lswitch_and_lrouter_iterate_by_lr(struct ovn_datapath *od,
     build_arp_resolve_flows_for_lrouter(od, lsi->lflows);
     build_check_pkt_len_flows_for_lrouter(od, lsi->lflows, lsi->lr_ports,
                                           &lsi->match, &lsi->actions,
-                                          lsi->meter_groups);
+                                          lsi->meter_groups, lsi->features);
     build_gateway_redirect_flows_for_lrouter(od, lsi->lflows, &lsi->match,
                                              &lsi->actions);
     build_arp_request_flows_for_lrouter(od, lsi->lflows, &lsi->match,
diff --git a/tests/ovn-northd.at b/tests/ovn-northd.at
index e7910e83c..c30715bfa 100644
--- a/tests/ovn-northd.at
+++ b/tests/ovn-northd.at
@@ -6082,7 +6082,8 @@  OVN_FOR_EACH_NORTHD_NO_HV([
 AT_SETUP([ovn -- gateway mtu check pkt larger flows])
 ovn_start
 
-check ovn-sbctl chassis-add ch1 geneve 127.0.0.1
+check ovn-sbctl chassis-add ch1 geneve 127.0.0.1 --\
+                set chassis ch1 other_config:ct-commit-nat-v2=true
 
 check ovn-nbctl ls-add sw0
 check ovn-nbctl ls-add sw1
@@ -6127,10 +6128,14 @@  AT_CHECK([grep -e "chk_pkt_len" -e "lr_in_larger_pkts" lr0flows | sed 's/table=.
   table=??(lr_in_chk_pkt_len  ), priority=0    , match=(1), action=(next;)
   table=??(lr_in_chk_pkt_len  ), priority=50   , match=(outport == "lr0-public"), action=(reg9[[1]] = check_pkt_larger(1514); next;)
   table=??(lr_in_larger_pkts  ), priority=0    , match=(1), action=(next;)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
 ])
 
 AT_CHECK([grep -E "lr_in_admission.*check_pkt_larger" lr0flows | sort], [0], [dnl
@@ -6145,6 +6150,10 @@  AT_CHECK([grep -E "lr_in_ip_input.*icmp6_error" lr0flows | sort], [0], [dnl
   table=3 (lr_in_ip_input     ), priority=150  , match=(inport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
 ])
 
+AT_CHECK([grep -E "lr_out_post_snat.*ct_commit_nat" lr0flows | sed 's/table=../table=??/' | sort], [0], [dnl
+  table=??(lr_out_post_snat   ), priority=100  , match=(icmp && flags.icmp_snat == 1), action=(ct_commit_nat(snat);)
+])
+
 # Clear the gateway-chassis for lr0-public
 check ovn-nbctl --wait=sb clear logical_router_port lr0-public gateway_chassis
 
@@ -6158,10 +6167,14 @@  AT_CHECK([grep -e "chk_pkt_len" -e "lr_in_larger_pkts" lr0flows | sed 's/table=.
   table=??(lr_in_chk_pkt_len  ), priority=0    , match=(1), action=(next;)
   table=??(lr_in_chk_pkt_len  ), priority=50   , match=(outport == "lr0-public"), action=(reg9[[1]] = check_pkt_larger(1514); next;)
   table=??(lr_in_larger_pkts  ), priority=0    , match=(1), action=(next;)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
 ])
 
 AT_CHECK([grep -E "lr_in_admission.*check_pkt_larger" lr0flows | sort], [0], [dnl
@@ -6176,6 +6189,10 @@  AT_CHECK([grep -E "lr_in_ip_input.*icmp6_error" lr0flows | sort], [0], [dnl
   table=3 (lr_in_ip_input     ), priority=150  , match=(inport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
 ])
 
+AT_CHECK([grep -E "lr_out_post_snat.*ct_commit_nat" lr0flows | sed 's/table=../table=??/' | sort], [0], [dnl
+  table=??(lr_out_post_snat   ), priority=100  , match=(icmp && flags.icmp_snat == 1), action=(ct_commit_nat(snat);)
+])
+
 # Set gateway_mtu_bypass to avoid check_pkt_larger() for tcp on lr0-public.
 check ovn-nbctl --wait=sb set logical_router_port lr0-public options:gateway_mtu_bypass=tcp
 
@@ -6187,10 +6204,14 @@  AT_CHECK([grep -e "chk_pkt_len" -e "lr_in_larger_pkts" lr0flows | sed 's/table=.
   table=??(lr_in_chk_pkt_len  ), priority=50   , match=(outport == "lr0-public"), action=(reg9[[1]] = check_pkt_larger(1514); next;)
   table=??(lr_in_chk_pkt_len  ), priority=55   , match=(outport == "lr0-public" && (tcp)), action=(next;)
   table=??(lr_in_larger_pkts  ), priority=0    , match=(1), action=(next;)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
 ])
 
 AT_CHECK([grep "lr_in_admission" lr0flows | grep -e "check_pkt_larger" -e "tcp" | sort], [0], [dnl
@@ -6212,14 +6233,22 @@  AT_CHECK([grep -e "chk_pkt_len" -e "lr_in_larger_pkts" lr0flows | sed 's/table=.
   table=??(lr_in_chk_pkt_len  ), priority=50   , match=(outport == "lr0-sw0"), action=(reg9[[1]] = check_pkt_larger(1414); next;)
   table=??(lr_in_chk_pkt_len  ), priority=55   , match=(outport == "lr0-public" && (tcp)), action=(next;)
   table=??(lr_in_larger_pkts  ), priority=0    , match=(1), action=(next;)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
 ])
 
 AT_CHECK([grep "lr_in_admission.*check_pkt_larger" lr0flows | sort], [0], [dnl
@@ -6238,6 +6267,10 @@  AT_CHECK([grep -E "lr_in_ip_input.*icmp6_error" lr0flows | sort], [0], [dnl
   table=3 (lr_in_ip_input     ), priority=150  , match=(inport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
 ])
 
+AT_CHECK([grep -E "lr_out_post_snat.*ct_commit_nat" lr0flows | sed 's/table=../table=??/' | sort], [0], [dnl
+  table=??(lr_out_post_snat   ), priority=100  , match=(icmp && flags.icmp_snat == 1), action=(ct_commit_nat(snat);)
+])
+
 # Set gateway_mtu_bypass to avoid check_pkt_larger() for tcp on lr0-sw0.
 check ovn-nbctl --wait=sb set logical_router_port lr0-sw0 options:gateway_mtu_bypass=tcp
 
@@ -6251,14 +6284,22 @@  AT_CHECK([grep -e "chk_pkt_len" -e "lr_in_larger_pkts" lr0flows | sed 's/table=.
   table=??(lr_in_chk_pkt_len  ), priority=55   , match=(outport == "lr0-public" && (tcp)), action=(next;)
   table=??(lr_in_chk_pkt_len  ), priority=55   , match=(outport == "lr0-sw0" && (tcp)), action=(next;)
   table=??(lr_in_larger_pkts  ), priority=0    , match=(1), action=(next;)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw0" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:01; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-public" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1500; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
 ])
 
 AT_CHECK([grep "lr_in_admission" lr0flows | grep -e "check_pkt_larger" -e "tcp" | sort], [0], [dnl
@@ -6277,16 +6318,19 @@  check ovn-nbctl --wait=sb clear logical_router_port lr0-public options
 ovn-sbctl dump-flows lr0 > lr0flows
 AT_CAPTURE_FILE([lr0flows])
 
-grep -e "chk_pkt_len" -e "lr_in_larger_pkts" lr0flows | sed 's/table=../table=??/' | sort
 AT_CHECK([grep -e "chk_pkt_len" -e "lr_in_larger_pkts" lr0flows | sed 's/table=../table=??/' | sort], [0], [dnl
   table=??(lr_in_chk_pkt_len  ), priority=0    , match=(1), action=(next;)
   table=??(lr_in_chk_pkt_len  ), priority=50   , match=(outport == "lr0-sw0"), action=(reg9[[1]] = check_pkt_larger(1414); next;)
   table=??(lr_in_chk_pkt_len  ), priority=55   , match=(outport == "lr0-sw0" && (tcp)), action=(next;)
   table=??(lr_in_larger_pkts  ), priority=0    , match=(1), action=(next;)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 10.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
-  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff01; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0), action=(icmp4_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=150  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0), action=(icmp6_error {reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip4.dst = ip4.src; ip4.src = 172.168.0.100; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-public" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:20:20:12:13; ip6.dst = ip6.src; ip6.src = fe80::200:20ff:fe20:1213; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip4 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp4_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip4.dst = ip4.src; ip4.src = 20.0.0.1; ip.ttl = 255; icmp4.type = 3; /* Destination Unreachable. */ icmp4.code = 4; /* Frag Needed and DF was Set. */ icmp4.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
+  table=??(lr_in_larger_pkts  ), priority=160  , match=(inport == "lr0-sw1" && outport == "lr0-sw0" && ip6 && reg9[[1]] && reg9[[0]] == 0 && ct.trk && ct.rpl && ct.dnat), action=(icmp6_error {flags.icmp_snat = 1; reg9[[0]] = 1; reg9[[1]] = 0; eth.dst = 00:00:00:00:ff:02; ip6.dst = ip6.src; ip6.src = fe80::200:ff:fe00:ff02; ip.ttl = 255; icmp6.type = 2; /* Packet Too Big. */ icmp6.code = 0; icmp6.frag_mtu = 1400; next(pipeline=ingress, table=0); };)
 ])
 
 check ovn-nbctl --wait=sb clear logical_router_port lr0-sw0 options
@@ -6319,6 +6363,12 @@  AT_CHECK([grep "lr_in_admission" lr0flows | grep -e "check_pkt_larger" | sort],
   table=0 (lr_in_admission    ), priority=50   , match=(eth.mcast && inport == "lr0-public"), action=(reg9[[1]] = check_pkt_larger(1518); xreg0[[0..47]] = 00:00:20:20:12:13; next;)
 ])
 
+check ovn-sbctl set chassis ch1 other_config:ct-commit-nat-v2=false
+check ovn-nbctl --wait=sb sync
+
+ovn-sbctl dump-flows lr0 > lr0flows
+AT_CHECK([grep -E "lr_out_post_snat.*ct_commit_nat" lr0flows], [1])
+
 AT_CLEANUP
 ])
 
diff --git a/tests/ovn.at b/tests/ovn.at
index 94f57d796..54e48e5aa 100644
--- a/tests/ovn.at
+++ b/tests/ovn.at
@@ -20575,12 +20575,12 @@  test_ip_packet_larger() {
         expected=${expected}0000000000000000000000000000
         echo $expected > br_phys_n1.expected
     else
-        src_ip=`ip_to_hex 172.168.0.100`
+        src_ip=`ip_to_hex 10 0 0 1`
         dst_ip=`ip_to_hex 10 0 0 3`
         # pkt len should be 146 (28 (icmp packet) + 118 (orig ip + payload))
         reply_pkt_len=008e
         ip_csum=fc97
-        icmp_reply=${src_mac}${dst_mac}08004500${reply_pkt_len}00004000fe01c55f
+        icmp_reply=${src_mac}${dst_mac}08004500${reply_pkt_len}00004000fe01686b
         icmp_reply=${icmp_reply}${src_ip}${dst_ip}0304${ip_csum}0000$(printf "%04x" $mtu)
         icmp_reply=${icmp_reply}4500${pkt_len}000000003f01c4dd
         icmp_reply=${icmp_reply}${orig_packet_l3}
@@ -20672,7 +20672,7 @@  test_ip6_packet_larger() {
 
     local ipv6_src=10000000000000000000000000000003
     local ipv6_dst=20000000000000000000000000000002
-    local ipv6_rt=20000000000000000000000000000001
+    local ipv6_rt=10000000000000000000000000000001
 
     local payload=0000000000000000000000000000000000000000
     local payload=${payload}0000000000000000000000000000000000000000
diff --git a/tests/system-ovn-kmod.at b/tests/system-ovn-kmod.at
index a81bae713..047a296eb 100644
--- a/tests/system-ovn-kmod.at
+++ b/tests/system-ovn-kmod.at
@@ -1196,7 +1196,7 @@  dnl check ovn-nbctl lr-lb-add lr lb1
 check ovn-nbctl set logical_router lr options:chassis=hv1
 check ovn-nbctl set logical_router_port lr-internal options:gateway_mtu=800
 
-check ovn-nbctl lr-nat-add lr snat 192.168.1.1 172.16.1.2/24
+check ovn-nbctl lr-nat-add lr snat 192.168.1.1 172.16.1.2
 
 check ovn-nbctl --wait=hv sync
 
@@ -1251,6 +1251,7 @@  NS_CHECK_EXEC([client], [$PYTHON3 ./client.py])
 
 dnl Expecting 2 outgoing packets and 2 fragments back - 8 lines total.
 OVS_WAIT_UNTIL([test "$(cat client.tcpdump | wc -l)" = "8"])
+AT_CHECK([test $(grep -c "need to frag (mtu 800)" server.tcpdump) -eq 1])
 
 ovn-appctl -t ovn-controller vlog/set info