Order of BGP communities

[Pavlos Parissis]

Hi,

Today, we noticed a difference in the order that communities were added between 1.6.3 and 1.4.5 version.

All exported routes pass through a function, which adds three communities:

function match_route_north()
{
    bgp_community.add((64813,lookup_live_id(net.ip)));
    bgp_community.add(DC_ID);
    bgp_community.add((64813,lookup_fabric_id(net.ip)));
    return (net ~ ACAST_PS_ADVERTISE && net ~ ANYCAST_NETWORKS_NORTH && !(net ~ ACAST_PS_DISABLED));
}

As you see we add first live_id (which is always 1000) and last the fabric_id(which is always 3).

With bird 1.6.3 version we see that live_id community is listed 1st:

1.17.1.143/32     dev lo [direct1 2017-06-07 15:30:29 1496842229] * (240)
        Type: device unicast univ
        BGP.origin: IGP
        BGP.as_path: 61115
        BGP.next_hop: 10.1.9.1
        BGP.local_pref: 0
        BGP.community: (64813,1000) (64815,100) (64813,3)

but with 1.4.5 version is listed as last:

1.17.16.143/32     dev lo [direct1 2017-03-10 11:24:36 1489141476] * (240)
        Type: device unicast univ
        BGP.origin: IGP
        BGP.as_path: 6115
        BGP.next_hop: 10.1.6.1
        BGP.local_pref: 0
        BGP.community: (64813,3) (61115,100) (64813,1000)


Does anyone know why ?


Cheers,
Pavlos

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