bgpd: Fix mixed remote-as for peer-groups when using auto (backport #21406)

bgpd/bgp_packet.c

@@ -1989,6 +1989,7 @@ static int bgp_open_receive(struct peer_connection *connection,
 			SET_FLAG(peer->as_type, AS_EXTERNAL);
 			UNSET_FLAG(peer->as_type, AS_INTERNAL);
 		}
+		(void)peer_sort(peer);
 	} else if (peer->as_type == AS_INTERNAL) {
 		if (remote_as != peer->bgp->as) {
 			if (bgp_debug_neighbor_events(peer))

bgpd/bgpd.c

@@ -1108,8 +1108,16 @@ static inline enum bgp_peer_sort peer_calc_sort(struct peer *peer)
 			assert(peer->group);
 			peer1 = listnode_head(peer->group->peer);
 
-			if (peer1)
+			if (peer1) {
+				/* AS_AUTO without INTERNAL/EXTERNAL bits means
+				 * the type is not yet resolved (no session up).
+				 * Treat as unestablished so it doesn't block
+				 * other members from being configured.
+				 */
+				if (peer1->as_type == AS_AUTO)
+					return BGP_PEER_INTERNAL;
 				return peer1->sort;
+			}
 		}
 		return BGP_PEER_INTERNAL;
 	}

tests/topotests/bgp_remote_as_auto/r1/frr.conf

@@ -17,6 +17,9 @@ router bgp 65001
  neighbor r1-eth1 interface remote-as auto
  neighbor r1-eth1 timers 1 3
  neighbor r1-eth1 timers connect 1
+ neighbor 192.168.1.5 remote-as internal
+ neighbor 192.168.1.5 timers 1 3
+ neighbor 192.168.1.5 timers connect 1
  address-family ipv4 unicast
   network 10.0.0.1/32
  exit-address-family

tests/topotests/bgp_remote_as_auto/r2/frr.conf

@@ -7,4 +7,7 @@ router bgp 65001
  neighbor 192.168.1.1 remote-as auto
  neighbor 192.168.1.1 timers 1 3
  neighbor 192.168.1.1 timers connect 1
+ neighbor 192.168.1.5 remote-as internal
+ neighbor 192.168.1.5 timers 1 3
+ neighbor 192.168.1.5 timers connect 1
 !

tests/topotests/bgp_remote_as_auto/r3/frr.conf

@@ -7,4 +7,7 @@ router bgp 65003
  neighbor 192.168.1.1 remote-as auto
  neighbor 192.168.1.1 timers 1 3
  neighbor 192.168.1.1 timers connect 1
+ neighbor 192.168.1.5 remote-as external
+ neighbor 192.168.1.5 timers 1 3
+ neighbor 192.168.1.5 timers connect 1
 !

tests/topotests/bgp_remote_as_auto/r5/frr.conf

@@ -0,0 +1,20 @@
+!
+int r5-eth0
+ ip address 192.168.1.5/24
+!
+router bgp 65001
+ no bgp ebgp-requires-policy
+ neighbor PG peer-group
+ neighbor 192.168.1.1 peer-group PG
+ neighbor 192.168.1.1 remote-as auto
+ neighbor 192.168.1.1 timers 1 3
+ neighbor 192.168.1.1 timers connect 1
+ neighbor 192.168.1.2 peer-group PG
+ neighbor 192.168.1.2 remote-as internal
+ neighbor 192.168.1.2 timers 1 3
+ neighbor 192.168.1.2 timers connect 1
+ neighbor 192.168.1.3 peer-group PG
+ neighbor 192.168.1.3 remote-as external
+ neighbor 192.168.1.3 timers 1 3
+ neighbor 192.168.1.3 timers connect 1
+!

tests/topotests/bgp_remote_as_auto/test_bgp_remote_as_auto.py

@@ -23,7 +23,7 @@
 
 
 def setup_module(mod):
-    topodef = {"s1": ("r1", "r2", "r3"), "s2": ("r1", "r4")}
+    topodef = {"s1": ("r1", "r2", "r3", "r5"), "s2": ("r1", "r4")}
     tgen = Topogen(topodef, mod.__name__)
     tgen.start_topology()
 
@@ -50,6 +50,7 @@ def test_bgp_remote_as_auto():
     r2 = tgen.gears["r2"]
     r3 = tgen.gears["r3"]
     r4 = tgen.gears["r4"]
+    r5 = tgen.gears["r5"]
 
     def _bgp_converge():
         output = json.loads(r1.vtysh_cmd("show bgp ipv4 unicast summary json"))
@@ -155,6 +156,40 @@ def _bgp_converge_external_unnumbered():
     _, result = topotest.run_and_expect(test_func, None, count=30, wait=1)
     assert result is None, "Can't see automatic unnumbered eBGP peering"
 
+    def _bgp_converge_peer_group():
+        output = json.loads(r5.vtysh_cmd("show bgp ipv4 unicast summary json"))
+        expected = {
+            "peers": {
+                "192.168.1.1": {
+                    "hostname": "r1",
+                    "remoteAs": 65001,
+                    "localAs": 65001,
+                    "state": "Established",
+                },
+                "192.168.1.2": {
+                    "hostname": "r2",
+                    "remoteAs": 65001,
+                    "localAs": 65001,
+                    "state": "Established",
+                },
+                "192.168.1.3": {
+                    "hostname": "r3",
+                    "remoteAs": 65003,
+                    "localAs": 65001,
+                    "state": "Established",
+                },
+            }
+        }
+        return topotest.json_cmp(output, expected)
+
+    test_func = functools.partial(
+        _bgp_converge_peer_group,
+    )
+    _, result = topotest.run_and_expect(test_func, None, count=30, wait=1)
+    assert (
+        result is None
+    ), "Peer-group with mixed remote-as auto/internal members failed to establish"
+
 
 if __name__ == "__main__":
     args = ["-s"] + sys.argv[1:]