Re: BMP Adj-RIB-Out post-policy support

[David Petera via Bird-users]

Hi Matthieu,

thanks a lot for the patch of BMP in v3!
I put it in our internal backlog and as soon as this busy period* is 
over, we will review it and hopefully merge it.
Then we can also proceed further in the Adj-RIB-Out post-policy support.
You mentioned that you rely on BMP quite a lot, can I ask you which BMP 
listener do you use?
I will soon get back to writing a test for BMP (initially prompted by 
your previous mail concerning BMP in v3) and I would be curious about 
your actual setup.
Will most likely use Rotonda and/or pmbmpd utility, but maybe you are 
using something else entirely.

WIP of the test can be seen on a branch here: 
https://gitlab.nic.cz/labs/bird-tools/-/tree/bmp_test/netlab/cf-bgp-bmp?ref_type=heads 

(note it is not in a working state yet)

I would also like the test to be ready for the eventual support of 
Adj-RIB-Out post-policy.

Thanks again and happy routing!
David

*most of our team is either finishing EVPN or writing drafts for the 
upcoming IETF))

David Petera (he/him) | BIRD Tech Support | CZ.NIC, z.s.p.o.

On 1/15/26 11:50, Matthieu Gouel via Bird-users wrote:

Dear Maria,

Thanks a lot for the review and for the pointers!

Indeed, my initial patch is wrong. I was sourcing updates from the 
main table, which effectively means I was exporting the RIB as updates 
and calling that ADJ-RIB-Out.

I tried to fix the implementation to use the actual |out_table|, but I 
kept running into crashes. From what I can tell, this is because the 
out table is an internal table and I didn’t manage to correctly create 
or attach a channel to it without hitting invalid states.

Given your comment about |thread-next| handling |out_table| very 
differently, I wondered whether it might make more sense to target 
that branch instead. Before going further in that direction, I wanted 
to double-check that BMP ADJ-RIB-In Route Monitoring was working 
properly there first.

I had a suspicion it wasn’t, since I had already tested early BIRD v3 
releases back when they came out and saw issues at the time (mentioned 
it on the mailing list but that was a busy period). After retesting, 
it turns out ADJ-RIB-In RM was indeed broken: my collector was only 
receiving End-of-RIB messages, with no actual route updates.

Since I had a good test setup handy, I dug into it and found a few 
issues that prevented IPv4 and IPv6 updates from being sent as BMP 
Route Monitoring messages. Here is the result:

https://github.com/matthieugouel/bird/commit/835ea3fae7f162105621bd773a078bd7ad36ec4d

I compared the BMP output against BIRD v2 and got matching behavior, 
using v2 as the reference. That said, given my C skills, this would 
definitely need a careful review before merging.

This is a bit of a detour from the original ADJ-RIB-Out goal, but I 
think getting the current BMP implementation in v3 into a solid state 
is probably a good first step before extending it further.

Thanks again for the feedback, happy to iterate or adjust direction 
based on what you think makes the most sense.

Best,
Matthieu


On Wednesday, 14 January 2026 at 15:39, Maria Matejka via Bird-users 
<bird-users@network.cz> wrote:

Dear Matthieu,

thank you for your patch!

On Wed, Jan 14, 2026 at 07:50:29AM +0000, Matthieu Gouel via 
Bird-users wrote:

    Currently, the (preliminary) BMP protocol implementation in BIRD
    does not support ADJ-RIB-Out monitoring. Only ADJ-RIB-In pre- and
    post-policy are supported at the moment.

    I have implemented support for ADJ-RIB-Out post-policy
    monitoring, which is relatively straightforward to add. The
    proposed implementation is available here:

    
https://github.com/CZ-NIC/bird/compare/master…matthieugouel:bird:bmp-adj-rib-out

    I have not implemented ADJ-RIB-Out pre-policy yet, as this would
    require more intrusive changes related to export tables.

I suspect that you don’t export from the |out_table| actually, you 
are using the main table instead if I read your patch correctly.

Also, your commit is missing documentation in |doc/bird.sgml|, as 
well as supported RFC in |proto/bmp/bmp.c| header.

You should also check mergability of your patch with the thread-next 
branch, as if I remember correctly, the out_table is implemented 
there completely differently.

Last but not least, I would love to see a commit on top of 
https://gitlab.nic.cz/labs/bird-tools/ in the |netlab| folder as an 
automatic test suite. David Petera (cc) is currently working on BMP 
tests for other scenarios, and it might be worth consulting this 
topic with him.

    I would be interested to know whether this is something you would
    consider merging. More generally, is there interest in extending
    BMP support in BIRD with additional features? I know that BMP is
    still marked as preliminary and not production-ready, but it is a
    protocol I personally rely on quite heavily.

BMP should be production-worthy and we do consider merging BMP 
extensions.

Please note, however, that BGP export is a very hot path and one 
should very much think about what is being done there, 
performance-wise. That deserves at least a warning in the 
documentation, so that somebody doesn’t unknowingly turn their router 
into a traffic generator.

More specifically, the BMP implementation still severely lacks update 
merging, and there have been some very serious thoughts about merging 
the BMP TX with BGP TX data structures (which would do the update 
merging). With that, I would suggest informing us about your plans 
beforehand, so that we can plan around accordingly.

Have a nice day!
Maria

–
Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.