Add time exceeded flow for fip

Add "ip4.src == <external_ip>" to match for distinguish between
external router gateway and floatingIP to handle time exceeded
packet.

Signed-off-by: Huanghailun <[email protected]>

Author: hailun.huang

Diff for: northd/northd.c

@@ -14680,6 +14680,42 @@ build_lrouter_arp_nd_for_datapath(struct ovn_datapath *od,
     }
 }
 
+static void
+build_time_exceeded_flow_for_dnat_and_snat(struct ovn_port *op,
+                                           struct hmap *lflows, struct ds *ip_ds,
+                                           struct ds *match, struct ds *actions,
+                                           const struct shash *meter_groups)
+{
+    if (is_l3dgw_port(op)) {
+        for (int i = 0; i < op->od->nbr->n_nat; i++) {
+            ds_clear(match);
+            ds_clear(actions);
+            ds_clear(ip_ds);
+            struct ovn_nat *nat_entry = &op->od->nat_entries[i];
+            if (!strcmp(nat_entry->nb->type, "dnat_and_snat")) {
+                ds_put_format(match, "ip4.src == %s && ", nat_entry->nb->external_ip);
+                ds_put_cstr(ip_ds, "ip4.dst <-> ip4.src");
+                ds_put_format(match,
+                              "inport == %s && ip4 && "
+                              "ip.ttl == {0, 1} && !ip.later_frag", op->json_key);
+                ds_put_format(actions,
+                              "icmp4 {"
+                              "eth.dst <-> eth.src; "
+                              "icmp4.type = 11; /* Time exceeded */ "
+                              "icmp4.code = 0; /* TTL exceeded in transit */ "
+                              "%s ; ip.ttl = 254; "
+                              "outport = %s; flags.loopback = 1; output; };",
+                              ds_cstr(ip_ds), op->json_key);
+                ovn_lflow_add_with_hint__(lflows, op->od, S_ROUTER_IN_IP_INPUT,
+                    30, ds_cstr(match), ds_cstr(actions), NULL,
+                    copp_meter_get(COPP_ICMP4_ERR, op->od->nbr->copp,
+                                   meter_groups),
+                    &op->nbrp->header_);
+            }
+        }
+    }
+}
+
 /* Logical router ingress table 3: IP Input for IPv4. */
 static void
 build_lrouter_ipv4_ip_input(struct ovn_port *op,
@@ -14730,6 +14766,8 @@ build_lrouter_ipv4_ip_input(struct ovn_port *op,
 
     /* ICMP time exceeded */
     struct ds ip_ds = DS_EMPTY_INITIALIZER;
+    build_time_exceeded_flow_for_dnat_and_snat(op, lflows, &ip_ds,
+                                               match, actions, meter_groups);
     for (int i = 0; i < op->lrp_networks.n_ipv4_addrs; i++) {
         ds_clear(match);
         ds_clear(actions);