Fix IPv4 routes with IPv6 link local next hops installed in FPM (#8740)

* Description: Currently IPv4 routes with IPv6 link local next hops are
not properly installed in FPM.
Reason is the netlink decoding truncates the ipv6 LL address to 4 byte
ipv4 address.

Ex : fe80:: is directly converted to ipv4 and it results in 254.128.0.0
as next hop for below routes

show ip route
Codes: K - kernel route, C - connected, S - static, R - RIP,
O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
F - PBR, f - OpenFabric,
> - selected route, * - FIB route, q - queued, r - rejected, b - backup

B>* 2.1.0.0/16 [200/0] via fe80::268a:7ff:fed0:d40, Ethernet0, weight 1,
02:22:26
B>* 5.1.0.0/16 [200/0] via fe80::268a:7ff:fed0:d40, Ethernet0, weight 1,
02:22:26
B>* 10.1.0.2/32 [200/0] via fe80::268a:7ff:fed0:d40, Ethernet0, weight
1, 02:22:26

Hence this fix converts the ipv6-LL address to ipv4-LL (169.254.0.1)
address before sending it to FPM. This is inline with how these types of
routes are currently programmed into kernel.

Signed-off-by: Nikhil Kelapure <[email protected]>

Author: nkelapur

src/sonic-frr/patch/0011-Ipv4-Link-local-address-for-Ipv6-linl-local-nexthop.patch

@@ -0,0 +1,55 @@
+diff --git a/zebra/zebra_fpm.c b/zebra/zebra_fpm.c
+index 7b0611bf9..b5582ea35 100644
+--- a/zebra/zebra_fpm.c
++++ b/zebra/zebra_fpm.c
+@@ -288,6 +288,9 @@ static void zfpm_start_connect_timer(const char *reason);
+ static void zfpm_start_stats_timer(void);
+ static void zfpm_mac_info_del(struct fpm_mac_info_t *fpm_mac);
+ 
++static const char ipv4_ll_buf[16] = "169.254.0.1";
++union g_addr ipv4ll_gateway;
++
+ /*
+  * zfpm_thread_should_yield
+  */
+@@ -1988,6 +1991,9 @@ static int zfpm_init(struct thread_master *master)
+ 	zfpm_stats_init(&zfpm_g->last_ivl_stats);
+ 	zfpm_stats_init(&zfpm_g->cumulative_stats);
+ 
++	memset(&ipv4ll_gateway, 0, sizeof(ipv4ll_gateway));
++	inet_pton(AF_INET, ipv4_ll_buf, &ipv4ll_gateway.ipv4);
++
+ 	install_node(&zebra_node);
+ 	install_element(ENABLE_NODE, &show_zebra_fpm_stats_cmd);
+ 	install_element(ENABLE_NODE, &clear_zebra_fpm_stats_cmd);
+diff --git a/zebra/zebra_fpm_netlink.c b/zebra/zebra_fpm_netlink.c
+index 60ea7f97e..0f8ba5413 100644
+--- a/zebra/zebra_fpm_netlink.c
++++ b/zebra/zebra_fpm_netlink.c
+@@ -221,7 +221,12 @@ static int netlink_route_info_add_nh(struct netlink_route_info *ri,
+ 
+ 	if (nexthop->type == NEXTHOP_TYPE_IPV6
+ 	    || nexthop->type == NEXTHOP_TYPE_IPV6_IFINDEX) {
+-		nhi.gateway = &nexthop->gate;
++		/* Special handling for IPv4 route with IPv6 Link Local next hop
++		 */
++		if (ri->af == AF_INET)
++			nhi.gateway = &ipv4ll_gateway;
++		else
++			nhi.gateway = &nexthop->gate;
+ 	}
+ 
+ 	if (nexthop->type == NEXTHOP_TYPE_IFINDEX) {
+diff --git a/zebra/zebra_fpm_private.h b/zebra/zebra_fpm_private.h
+index c169ee8c2..13415c7e1 100644
+--- a/zebra/zebra_fpm_private.h
++++ b/zebra/zebra_fpm_private.h
+@@ -97,6 +97,8 @@ extern int zfpm_netlink_encode_mac(struct fpm_mac_info_t *mac, char *in_buf,
+ 
+ extern struct route_entry *zfpm_route_for_update(rib_dest_t *dest);
+ 
++extern union g_addr ipv4ll_gateway;
++
+ #ifdef __cplusplus
+ }
+ #endif

src/sonic-frr/patch/series

@@ -8,3 +8,4 @@
 0009-Add-bgp-bestpath-peer-type-multipath-relax.patch
 0009-Link-local-scope-was-not-set-while-binding-socket-for-bgp-ipv6-link-local-neighbors.patch
 0010-remove-doc-png-install.patch
+0011-Ipv4-Link-local-address-for-Ipv6-linl-local-nexthop.patch