[ixpmanager] BIRD / Route Server: Load-balancing traffic for member with multiple connections

[Salvador Bertenbreiter]

Hi André,
Great point, I think MED should solve the issue of which one is the
preferred gateway.

About Add Path Tx, I will read more about that, it sounds like a great
solution to offer multi-site balance solution using ECMP.

Best regards


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El El vie, 19 jun. 2026 a la(s) 11:06, Kyle Spencer via ixpmanager <
ixpmanager at inex.ie> escribió:

> Thanks for raising this.
>
> We are multi-site and some customers have multi-site redundancy. They
> manage flows by remotely enabling/disabling interfaces at either end. This
> seems like a much better solution.
>
> Might be good to add something about this to the docs :)
>
> On Fri, Jun 19, 2026 at 9:16 AM André Grüneberg via ixpmanager <
> ixpmanager at inex.ie> wrote:
>
>> Dear Salvador,
>>
>> It's part of the features of a route server that it only sends one -- the
>> "best path" -- route to it's neighbors.
>> I assume the tie breaker in your case will be the router ID (see
>> https://bird.nic.cz/doc/bird-2.17.5.html#bgp-route-select-rules).
>> If the peer is announcing multiple prefixes, they could set e.g.
>> different MEDs for each prefix, so Bird would have some earlier tie breaks
>> towards the other router.
>>
>> Besides all that, you could enable Add Path Tx. This will give the peers'
>> routers the chance to employ ECMP (or their own policies FWIW).
>>
>> We have enabled this on our route servers for quite some time now. It's
>> just adding a line "add paths tx;" to the channel in the BGP protocols in
>> the Bird config.
>>
>> You may find this in our skinned version of the Bird config:
>>
>> https://github.com/bcix/IXP-Manager/blob/f5acc6bfdee8479041623479b9606e5c2033f098/resources/skins/bcix/api/v4/router/server/bird2/rs01/neighbors.foil.php#L373
>> Maybe Barry wants to add this feature to the default distribution?
>>
>> Unfortunately not all peers' routers have Add Path Rx enabled on their
>> side. So, you may want to educate your peers to enable it for BGP sessions
>> with route servers.
>>
>> Hope this helps,
>> André
>>
>> On Fri, 19 Jun 2026 at 04:26, Salvador Bertenbreiter via ixpmanager <
>> ixpmanager at inex.ie> wrote:
>>
>>> Hi community,
>>>
>>> I hope you are doing well.
>>>
>>> We have a case involving a member with two separate connections to the
>>> peering LAN. Each connection has its own IP address, and both sessions are
>>> established with our Route Server.
>>>
>>> The member is concerned because all downstream traffic, from their
>>> perspective, is currently being received through only one of the two
>>> connections.
>>>
>>> I checked the Looking Glass, and both connections are announcing the
>>> same prefixes with the same AS-PATH. However, BIRD consistently selects all
>>> prefixes as primary via only one of the two sessions.
>>>
>>> The member mentioned that they are not able to announce more-specific
>>> prefixes from one router and less-specific prefixes from the other router,
>>> which would otherwise be a possible way to influence traffic distribution.
>>>
>>> I was wondering if there is any recommended way to achieve some form of
>>> load-balancing in this scenario. Specifically:
>>>
>>>    1. Is it possible for the Route Server / BIRD to "load-balance"
>>>    between two equivalent next-hops for the same prefix, so that downstream
>>>    traffic towards the member can be distributed across both connections?
>>>    2. If ECMP is not supported or not recommended in this context, is
>>>    there a way in IXP Manager or BIRD to influence which session is preferred?
>>>    For example, can we assign a higher local preference to one of the member’s
>>>    sessions so that the Route Server selects that connection as the primary
>>>    next-hop?
>>>    3. More generally, what would be the recommended operational
>>>    approach for handling members with multiple connections announcing the same
>>>    prefixes to the Route Server?
>>>
>>> Any guidance or best practices would be greatly appreciated.
>>>
>>> Best regards,
>>>
>>> Salvador Bertenbreiter
>>> _______________________________________________
>>> INEX IXP Manager mailing list
>>> ixpmanager at inex.ie
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>>>
>>
>>
>> --
>> André Grüneberg, Managing Director
>> andre.grueneberg at bcix.de
>> +49 30 2332195 42
>>
>> BCIX Management GmbH
>> Albrechtstr. 110
>> 12103 Berlin
>> Germany
>>
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>
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