SRv6 BGP SID reachability

bgpd/bgp_nht.c

@@ -116,24 +116,36 @@ static int bgp_isvalid_nexthop_for_mplsovergre(struct bgp_nexthop_cache *bnc,
 static int bgp_isvalid_nexthop_for_mpls(struct bgp_nexthop_cache *bnc,
 					struct bgp_path_info *path)
 {
+	return (bnc && (bnc->nexthop_num > 0 &&
+			(CHECK_FLAG(path->flags, BGP_PATH_ACCEPT_OWN) ||
+			 CHECK_FLAG(bnc->flags, BGP_NEXTHOP_LABELED_VALID) ||
+			 bgp_isvalid_nexthop_for_ebgp(bnc, path) ||
+			 bgp_isvalid_nexthop_for_mplsovergre(bnc, path))));
+}
+
+static bool bgp_isvalid_nexthop_for_l3vpn(struct bgp_nexthop_cache *bnc,
+					  struct bgp_path_info *path)
+{
+	if (bgp_zebra_num_connects() == 0)
+		return 1;
+
+	if (path->attr->srv6_l3vpn || path->attr->srv6_vpn) {
+		/* In the case of SRv6-VPN, we need to track the reachability to the
+		 * SID (in other words, IPv6 address). We check that the SID is
+		 * available in the BGP update; then if it is available, we check
+		 * for the nexthop reachability.
+		 */
+		if (bnc && (bnc->nexthop_num > 0 && bgp_isvalid_nexthop(bnc)))
+			return 1;
+		return 0;
+	}
 	/*
-	 * - In the case of MPLS-VPN, the label is learned from LDP or other
+	 * In the case of MPLS-VPN, the label is learned from LDP or other
 	 * protocols, and nexthop tracking is enabled for the label.
 	 * The value is recorded as BGP_NEXTHOP_LABELED_VALID.
-	 * - In the case of SRv6-VPN, we need to track the reachability to the
-	 * SID (in other words, IPv6 address). As in MPLS, we need to record
-	 * the value as BGP_NEXTHOP_SID_VALID. However, this function is
-	 * currently not implemented, and this function assumes that all
-	 * Transit routes for SRv6-VPN are valid.
 	 * - Otherwise check for mpls-gre acceptance
 	 */
-	return (bgp_zebra_num_connects() == 0 ||
-		(bnc && (bnc->nexthop_num > 0 &&
-			 (CHECK_FLAG(path->flags, BGP_PATH_ACCEPT_OWN) ||
-			  CHECK_FLAG(bnc->flags, BGP_NEXTHOP_LABELED_VALID) ||
-			  bnc->bgp->srv6_enabled ||
-			  bgp_isvalid_nexthop_for_ebgp(bnc, path) ||
-			  bgp_isvalid_nexthop_for_mplsovergre(bnc, path)))));
+	return bgp_isvalid_nexthop_for_mpls(bnc, path);
 }
 
 static void bgp_unlink_nexthop_check(struct bgp_nexthop_cache *bnc)
@@ -496,7 +508,7 @@ int bgp_find_or_add_nexthop(struct bgp *bgp_route, struct bgp *bgp_nexthop,
 	else if (safi == SAFI_UNICAST && pi &&
 		 pi->sub_type == BGP_ROUTE_IMPORTED && pi->extra &&
 		 pi->extra->num_labels && !bnc->is_evpn_gwip_nexthop)
-		return bgp_isvalid_nexthop_for_mpls(bnc, pi);
+		return bgp_isvalid_nexthop_for_l3vpn(bnc, pi);
 	else if (safi == SAFI_MPLS_VPN && pi &&
 		 pi->sub_type != BGP_ROUTE_IMPORTED)
 		/* avoid not redistributing mpls vpn routes */
@@ -1045,8 +1057,11 @@ static int make_prefix(int afi, struct bgp_path_info *pi, struct prefix *p)
 		break;
 	case AFI_IP6:
 		p->family = AF_INET6;
-
-		if (is_bgp_static) {
+		if (pi->attr && pi->attr->srv6_l3vpn) {
+			IPV6_ADDR_COPY(&(p->u.prefix6),
+				       &(pi->attr->srv6_l3vpn->sid));
+			p->prefixlen = IPV6_MAX_BITLEN;
+		} else if (is_bgp_static) {
 			p->u.prefix6 = p_orig->u.prefix6;
 			p->prefixlen = p_orig->prefixlen;
 		} else {
@@ -1294,8 +1309,9 @@ void evaluate_paths(struct bgp_nexthop_cache *bnc)
 		    && (path->attr->evpn_overlay.type
 			!= OVERLAY_INDEX_GATEWAY_IP)) {
 			bnc_is_valid_nexthop =
-				bgp_isvalid_nexthop_for_mpls(bnc, path) ? true
-									: false;
+				bgp_isvalid_nexthop_for_l3vpn(bnc, path)
+					? true
+					: false;
 		} else if (safi == SAFI_MPLS_VPN &&
 			   path->sub_type != BGP_ROUTE_IMPORTED) {
 			/* avoid not redistributing mpls vpn routes */

doc/user/bgp.rst

@@ -3172,6 +3172,31 @@ L3VPN SRv6
    Specify the SRv6 locator to be used for SRv6 L3VPN. The Locator name must
    be set in zebra, but user can set it in any order.
 
+L3VPN SRv6 SID reachability
+---------------------------
+
+In the context of IPv4 L3VPN over SRv6 specific usecase, 2001:db8:12::2
+is the peer IPv6 address of r2, and 2001:db8:2:2:: is the SRv6 SID
+advertised by router r2 for prefix P. On r1, the SID reachability is
+checked in order to install the prefix P. The below output indicates
+that the 2001:db8:2:2:: prefix is valid.
+
+
+.. code-block:: frr
+
+   r1# show bgp nexthop detail 
+   Current BGP nexthop cache:
+    2001:db8:2:2:: valid [IGP metric 0], #paths 4
+     gate 2001:db8:12::2, if eth0
+     Last update: Tue Nov 14 10:36:28 2023
+     Paths:
+       1/1 192.168.2.0/24 VRF vrf10 flags 0x4018
+       1/3 192.168.2.0/24 RD 65002:10 VRF default flags 0x418
+    2001:db8:12::2 valid [IGP metric 0], #paths 0, peer 2001:db8:12::2
+     if eth0
+     Last update: Tue Nov 14 10:36:26 2023
+     Paths:
+
 General configuration
 ^^^^^^^^^^^^^^^^^^^^^
 

tests/topotests/bgp_srv6_sid_reachability/c11/staticd.conf

@@ -0,0 +1,4 @@
+!
+ip route 0.0.0.0/0 192.168.1.254
+ipv6 route ::/0 2001:1::ffff
+!

tests/topotests/bgp_srv6_sid_reachability/c11/zebra.conf

@@ -0,0 +1,6 @@
+hostname c11
+!
+interface eth0
+ ip address 192.168.1.1/24
+ ipv6 address 2001:1::1/64
+!

tests/topotests/bgp_srv6_sid_reachability/c12/staticd.conf

@@ -0,0 +1,4 @@
+!
+ip route 0.0.0.0/0 192.168.1.254
+ipv6 route ::/0 2001:1::ffff
+!

tests/topotests/bgp_srv6_sid_reachability/c12/zebra.conf

@@ -0,0 +1,6 @@
+hostname c12
+!
+interface eth0
+ ip address 192.168.1.1/24
+ ipv6 address 2001:1::1/64
+!

tests/topotests/bgp_srv6_sid_reachability/c21/staticd.conf

@@ -0,0 +1,4 @@
+!
+ip route 0.0.0.0/0 192.168.2.254
+ipv6 route ::/0 2001:2::ffff
+!

tests/topotests/bgp_srv6_sid_reachability/c21/zebra.conf

@@ -0,0 +1,6 @@
+hostname c21
+!
+interface eth0
+ ip address 192.168.2.1/24
+ ipv6 address 2001:2::1/64
+!

tests/topotests/bgp_srv6_sid_reachability/c22/staticd.conf

@@ -0,0 +1,5 @@
+
+!
+ip route 0.0.0.0/0 192.168.2.254
+ipv6 route ::/0 2001:2::ffff
+!

tests/topotests/bgp_srv6_sid_reachability/c22/zebra.conf

@@ -0,0 +1,9 @@
+hostname c22
+!
+interface eth0
+ ip address 192.168.2.1/24
+ ipv6 address 2001:2::1/64
+!
+ip route 0.0.0.0/0 192.168.2.254
+ipv6 route ::/0 2001:2::ffff
+!

tests/topotests/bgp_srv6_sid_reachability/c31/staticd.conf

@@ -0,0 +1,4 @@
+!
+ip route 0.0.0.0/0 192.168.3.254
+ipv6 route ::/0 2001:3::ffff
+!

tests/topotests/bgp_srv6_sid_reachability/c31/zebra.conf

@@ -0,0 +1,6 @@
+hostname c31
+!
+interface eth0
+ ip address 192.168.3.1/24
+ ipv6 address 2001:3::1/64
+!

tests/topotests/bgp_srv6_sid_reachability/c32/staticd.conf

@@ -0,0 +1,4 @@
+!
+ip route 0.0.0.0/0 192.168.3.254
+ipv6 route ::/0 2001:3::ffff
+!

tests/topotests/bgp_srv6_sid_reachability/c32/zebra.conf

@@ -0,0 +1,6 @@
+hostname c32
+!
+interface eth0
+ ip address 192.168.3.1/24
+ ipv6 address 2001:3::1/64
+!

tests/topotests/bgp_srv6_sid_reachability/r1/bgpd.conf

@@ -0,0 +1,61 @@
+frr defaults traditional
+!
+hostname r1
+password zebra
+!
+log commands
+!
+router bgp 65001
+ bgp router-id 192.0.2.1
+ no bgp ebgp-requires-policy
+ no bgp default ipv4-unicast
+ neighbor 2001:db8:12::2 remote-as 65002
+ neighbor 2001:db8:12::2 timers 3 10
+ neighbor 2001:db8:12::2 timers connect 1
+ neighbor 2001:db8:12::2 capability extended-nexthop
+ neighbor 2001:db8:13::3 remote-as 65001
+ neighbor 2001:db8:13::3 timers 3 10
+ neighbor 2001:db8:13::3 timers connect 1
+ neighbor 2001:db8:13::3 capability extended-nexthop
+ !
+ segment-routing srv6
+  locator default
+ !
+ address-family ipv4 vpn
+  neighbor 2001:db8:12::2 activate
+  neighbor 2001:db8:13::3 activate
+ exit-address-family
+ !
+!
+router bgp 65001 vrf vrf10
+ bgp router-id 192.0.2.1
+ !
+ address-family ipv4 unicast
+  redistribute connected
+  sid vpn export 1
+  rd vpn export 65001:10
+  rt vpn both 0:10
+  import vpn
+  export vpn
+ exit-address-family
+ !
+!
+router bgp 65001 vrf vrf20
+ bgp router-id 192.0.2.1
+ !
+ address-family ipv4 unicast
+  redistribute connected
+  sid vpn export 2
+  rd vpn export 65001:20
+  rt vpn both 0:20
+  import vpn
+  export vpn
+ exit-address-family
+ !
+!
+interface eth0
+ mpls bgp forwarding
+!
+interface eth1
+ mpls bgp forwarding
+!

tests/topotests/bgp_srv6_sid_reachability/r1/staticd.conf

@@ -0,0 +1,4 @@
+!
+ipv6 route 2001:db8:2:2::/64 2001:db8:12::2
+ipv6 route 2001:db8:3:3::/64 2001:db8:13::3
+!

tests/topotests/bgp_srv6_sid_reachability/r1/zebra.conf

@@ -0,0 +1,32 @@
+log file zebra.log
+!
+hostname r1
+!
+interface lo
+ ipv6 address 2001:db8:1:1::1/128
+!
+interface eth0
+ ipv6 address 2001:db8:12::1/64
+!
+interface eth1
+ ipv6 address 2001:db8:13::1/64
+!
+interface eth2 vrf vrf10
+ ip address 192.168.1.254/24
+!
+interface eth3 vrf vrf20
+ ip address 192.168.1.254/24
+!
+segment-routing
+ srv6
+  locators
+   locator default
+    prefix 2001:db8:1:1::/64
+  !
+ !
+!
+ip forwarding
+ipv6 forwarding
+!
+line vty
+!

tests/topotests/bgp_srv6_sid_reachability/r2/bgpd.conf

@@ -0,0 +1,50 @@
+frr defaults traditional
+!
+hostname r2
+password zebra
+!
+log commands
+!
+router bgp 65002
+ bgp router-id 192.0.2.2
+ no bgp ebgp-requires-policy
+ no bgp default ipv4-unicast
+ neighbor 2001:db8:12::1 remote-as 65001
+ neighbor 2001:db8:12::1 timers 3 10
+ neighbor 2001:db8:12::1 timers connect 1
+ neighbor 2001:db8:12::1 capability extended-nexthop
+ !
+ segment-routing srv6
+  locator default
+ !
+ address-family ipv4 vpn
+  neighbor 2001:db8:12::1 activate
+ exit-address-family
+ !
+!
+router bgp 65002 vrf vrf10
+ bgp router-id 192.0.2.2
+ !
+ address-family ipv4 unicast
+  redistribute connected
+  sid vpn export 1
+  rd vpn export 65002:10
+  rt vpn both 0:10
+  import vpn
+  export vpn
+ exit-address-family
+ !
+!
+router bgp 65002 vrf vrf20
+ bgp router-id 192.0.2.2
+ !
+ address-family ipv4 unicast
+  redistribute connected
+  sid vpn export 2
+  rd vpn export 65002:20
+  rt vpn both 0:20
+  import vpn
+  export vpn
+ exit-address-family
+ !
+!

tests/topotests/bgp_srv6_sid_reachability/r2/staticd.conf

@@ -0,0 +1,4 @@
+!
+ipv6 route 2001:db8:1:1::/64 2001:db8:12::1
+ipv6 route 2001:db8:3:3::/64 2001:db8:12::1
+!

tests/topotests/bgp_srv6_sid_reachability/r2/zebra.conf

@@ -0,0 +1,29 @@
+log file zebra.log
+!
+hostname r2
+!
+interface lo
+ ipv6 address 2001:db8:2:2::1/128
+!
+interface eth0
+ ipv6 address 2001:db8:12::2/64
+!
+interface eth1 vrf vrf10
+ ip address 192.168.2.254/24
+!
+interface eth2 vrf vrf20
+ ip address 192.168.2.254/24
+!
+segment-routing
+ srv6
+  locators
+   locator default
+    prefix 2001:db8:2:2::/64
+  !
+ !
+!
+ip forwarding
+ipv6 forwarding
+!
+line vty
+!