FRR rejects route from eBGP peer whose AS equals the confederation identifier

[rsingha108]

Description

When an external peer (ExaBGP) has an AS number equal to the confederation identifier (AS 65000), FRR does not install the route in RIB2 or propagate it to R3. In contrast, both GoBGP and Batfish accept the route and propagate it through the confederation normally.

Version

FRR version 10.1

How to reproduce

The test topology is: ExaBGP (AS 65000) → R2 (Member-AS 65010, Confed ID 65000) → R3 (Member-AS 65011, Confed ID 65000).

ExaBGP config (conf.ini):

process announce-routes {
    run python exabgp/example.py;
    encoder json;
}

neighbor 6.0.0.2 {
    router-id 6.0.0.3;
    local-address 6.0.0.3;
    local-as 65000;
    peer-as 65000;

    api {
        processes [announce-routes];
    }
}

ExaBGP route announcement (example.py):

announce route 100.0.0.0/8 next-hop self

R2 config (frr.conf):

router bgp 65010
  no bgp ebgp-requires-policy
  bgp confederation identifier 65000
  bgp confederation peers 65011
  neighbor 6.0.0.3 remote-as 65000
  neighbor 8.0.0.3 remote-as 65011
  neighbor 8.0.0.3 route-map SET_LOCAL_PREF out
exit
!
route-map SET_LOCAL_PREF permit 10
    set local-preference 100
exit
!

R3 config (frr.conf):

router bgp 65011
  no bgp ebgp-requires-policy
  bgp confederation identifier 65000
  bgp confederation peers 65010
  neighbor 8.0.0.2 remote-as 65010
exit
!

Expected Behavior

Based on GoBGP and Batfish behavior:

• R2 should accept the route from ExaBGP (100.0.0.0/8) into its RIB (AS_PATH: empty).
• R2 should propagate the route to R3 with AS_CONFED_SEQUENCE prepended: AS_PATH = (65010).

GoBGP result: R2 RIB ✅ (AS_PATH: empty), R3 RIB ✅ (AS_PATH: (65010))
Batfish result: R2 RIB ✅ (AS_PATH: empty), R3 RIB ✅ (AS_PATH: 65010)

Actual Behavior

FRR result: R2 RIB ❌ (no route), R3 RIB ❌ (no route)

FRR does not install the route at R2 at all. The route from ExaBGP (AS 65000) is rejected, likely because FRR sees the peer's AS (65000) matching the confederation identifier (65000) and applies self-AS / loop-detection semantics, preventing the route from being accepted. But both GoBGP and Batfish accept this route in the same configuration.

Additional context

No response

Checklist

• I have searched the open issues for this bug.
• I have not included sensitive information in this report.