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

[André Grüneberg]

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
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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

Geschäftsführer/Managing Directors: Jens Lietzmann, André Grüneberg
Handelsregister: Amtsgericht Charlottenburg, HRB 143581 B
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