2 BGP sessions to same neighbors ?

[Damien Clabaut]

As complement, here is the configuration on the switch side:
router bgp 16276
   router-id 0.0.0.1
   maximum-paths 2
   neighbor 192.168.0.11 remote-as 16276
   neighbor 192.168.0.11 update-source Loopback0
   neighbor 192.168.0.12 remote-as 16276
   neighbor 192.168.0.12 update-source Loopback0
   address-family ipv4
      neighbor 192.168.0.11 activate
      neighbor 192.168.0.12 activate

And it shows one established session and the other is "Active":

  Neighbor         V  AS           MsgRcvd   MsgSent  InQ OutQ  Up/Down
State  PfxRcd PfxAcc
  192.168.0.11     4  16276            208       192    0    0 00:01:18
Estab  5      5
  192.168.0.12     4  16276            189       199    0    0 02:51:57
Active       

On 06/12/2016 16:08, Damien Clabaut wrote:
> Hello,
>
> For performance reasons that do not deserve to be detailed here, I am
> trying to set up 2 separate BGP sessions between my Linux server running
> Bird and an Arista switch.
>
> The Linux machines has 2 IPs on loopback, i would like to initiate a
> connexion from each of them.
>
> I have IPs 192.168.0.11 and 192.168.0.12 on the server loopback, and
> 192.168.0.1 on the switch loopback.
>
> These machines are connected with two different bonds, each of which has
> an OSPF session writing to a different routing table.
>
> Thus, I have those routes and rules:
>
> [root at bz-perflab-3-vr] ip route show table 1
> 10.10.50.44/30 via 10.10.50.41 dev bond0.510  proto bird
> 192.168.0.1 via 10.10.50.41 dev bond0.510  proto bird
> 192.168.0.12 via 10.10.50.41 dev bond0.510  proto bird
>
> [root at bz-perflab-3-vr] ip route show table 2
> 10.10.50.40/30 via 10.10.50.45 dev bond1.511  proto bird
> 192.168.0.1 via 10.10.50.45 dev bond1.511  proto bird
> 192.168.0.11 via 10.10.50.45 dev bond1.511  proto bird
>
> [root at bz-perflab-3-vr] ip rule show
> 0:    from all lookup local
> 32752:    from 192.168.0.12 lookup 2
> 32753:    from 192.168.0.11 lookup 1
>
> When I ping 192.168.0.1, the output interface depends on the source I
> use. So, this works.
>
> However, I cannot set up both BGP sessions. One is established and the
> other is idle, which makes me think there is a limitation somewhere in
> Bird that prevents opening several sessions with the same neighbour.
>
> TCPdump on the interface that has the "idle" BGP session shows
> absolutely no traffic on port 179.
>
> My BGP configuration is as follows:
> protocol bgp bgp_bond0 {
>   import all;
>   export filter {
>     if proto = "static_bond0" then {
>       bgp_local_pref = 105;
>       accept;
>     }
>     reject;
>   };
>   local as 16276;
>   neighbor 192.168.0.1 as 16276;
>   source address 192.168.0.11;
>   multihop;
>   advertise ipv4;
> };
>
> protocol bgp bgp_bond1 {
>   import all;
>   export filter {
>     if proto = "static_bond1" then {
>       bgp_local_pref = 105;
>       accept;
>     }
>     reject;
>   };
>
>   local as 16276;
>   neighbor 192.168.0.1 as 16276;
>   source address 192.168.0.12;
>   multihop;
>   advertise ipv4;
> };
>
> Can you confirm this is a limitation in Bird ? Is there a reason for it,
> apart from the fact that it is a non-standard case ? Is there a way to
> bypass it ?
>
> Regards,
>

-- 
Damien Clabaut
Network Engineer
OVH.pl


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