FW: BIRD is not prepending ASN on EBGP export.

[Ochalski, Radoslaw]

Hi,

We have observed strange behavior where BIRD is not adding ASN on EBGP export.
Route is received on IBGP session within AS20940:

r04.border01.lon03.fab > bird show  config template bgp 4INTERECOR_ROUTERS
template bgp '4INTERECOR_ROUTERS' {
    local as 20940;
    neighbor as 20940;


r04.border01.lon03.fab> show route protocol 23.210.49.60__r24.lon02.ien for 20.135.0.0/16 all
Executing "/usr/sbin/birdc show route protocol '23.210.49.60__r24.lon02.ien' for 20.135.0.0/16 all"
Table master4:
20.135.0.0/16        unicast [23.210.49.60__r24.lon02.ien 2024-10-07] (100) [AS8075i]
        via 23.210.49.60 on ae1
        Type: BGP univ
        BGP.origin: IGP
        BGP.as_path: 8075
        BGP.next_hop: 23.210.49.60
        BGP.med: 4294967294
        BGP.local_pref: 350

Route ASPATH: 8075 which is expected.


We are exporting this route on EBGP session from private ASN 4290006033 <-> to private ASN: 4290006002:

r04.border01.lon03.fab> show route export 2a02:26f0:1880:3702::1__r01.stem01 for 20.135.0.0/16 all
Executing "/usr/sbin/birdc show route export '2a02:26f0:1880:3702::1__r01.stem01' for 20.135.0.0/16 all"
Table master4:
20.135.0.0/16        unicast [2.22.144.250__r01.sdn 2024-10-07 from 2.22.144.250] * (100) [AS8075i]
        via 23.210.49.60 on ae1
        Type: BGP univ
        BGP.origin: IGP
        BGP.as_path: 8075
        BGP.next_hop: 23.210.49.60
        BGP.med: 4294967294
        BGP.local_pref: 777

Route is received on 4290006002:
r01.stem01.lon03.fab> show route protocol 2a02:26f0:1880:3702::__r04.border01 for 20.135.0.0/16  all
Executing "/usr/sbin/birdc show route protocol '2a02:26f0:1880:3702::__r04.border01' for 20.135.0.0/16 all"
Table master4:
20.135.0.0/16        unicast [2a02:26f0:1880:3702::__r04.border01 2024-10-07] * (100) [AS8075i]
        via 2a02:26f0:1880:3702:: on ae4
        Type: BGP univ
        BGP.origin: IGP
        BGP.as_path: 4290006033 8075
        BGP.next_hop: 2a02:26f0:1880:3702:: fe80::b6db:91ff:fe8b:1eb4
        BGP.local_pref: 100

ASPATH: 4290006033 8075

We are missing AS 20940 on which essentially this prefix is received in our network!?
Is this behavior expected?



Kind Regards,

Radek Ochalski

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