FRR does not propagate route from R2 to R3 across inter-confederation eBGP session

[rsingha108]

Description

When two routers belong to different BGP confederations (R2 in confed 65000, R3 in confed 65001) and peer externally, FRR R2 receives a route from an external origin (AS 65201) but fails to advertise it to R3. Both GoBGP and Batfish propagate the route correctly with AS_PATH 65000 65201 at R3, prepending the confederation identifier as required by RFC 5065 §4.

Topology: ExaBGP (AS 65201) → R2 (Member-AS 101, Confed ID 65000) → R3 (Member-AS 201, Confed ID 65001)

Version

10.6

How to reproduce

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 65201;
    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 101
  no bgp ebgp-requires-policy
  bgp confederation identifier 65000
  neighbor 6.0.0.3 remote-as 65201
  neighbor 8.0.0.3 remote-as 65001
  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 201
  no bgp ebgp-requires-policy
  bgp confederation identifier 65001
  neighbor 8.0.0.2 remote-as external
exit
!

Expected behavior

R2 should advertise the route to R3 with the confederation identifier (65000) prepended to the AS_PATH:

• R2 RIB: route present, AS_PATH = 65201
• R3 RIB: route present, AS_PATH = 65000 65201

Cross-validation:

• GoBGP: R2 ✅ (AS_PATH: 65201), R3 ✅ (AS_PATH: 65000 65201)
• Batfish: R2 ✅ (AS_PATH: 65201), R3 ✅ (AS_PATH: 65000 65201)

Actual behavior

FRR:

• R2 RIB: route present ✅ (AS_PATH: 65201)
• R3 RIB: no route ❌

R2 accepts the route from ExaBGP but does not propagate it to R3 across the inter-confederation eBGP session. Both GoBGP and Batfish successfully propagate in the same scenario.

Additional context

No response

Checklist

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