Hi Stefan,

On Wed, Apr 08, 2026 at 08:54:52AM +0000, Stefan Pisjak wrote:

I’ve searched through the documentation/this mailing list, but I haven’t found anyone trying to build a similar filter so far.

I’m trying to build a filter to only allow BGP routes if the “host part” of ip from matches the route that is being announced, e.g.:

10.0.1.2 is allowed to announce 10.100.1.2/32 10.0.1.3 is allowed to announce 10.100.1.3/32 […] 10.0.X.Y is allowed to announce 10.100.X.Y/32

The easiest way would probably be to extend the FI_BITAND and FI_BITOR operators for not only T_INT but also T_IP. Relevant code is in filter/f-inst.c, test file is filter/test.conf, feel free to send a patch.

These two operators are currently in BIRD 3 only because the weren’t needed in BIRD 2; feel free to backport them if needed.

But as far as I can tell, it’s not possible to somehow convert the type ip to type quad or something like that. Is there a better way to build this filter, or can you somehow create a new variable of the type ip and modify it or convert the ip to a quad and then do the manipulations?

Explicit type conversion of this kind is something much harder to implement in a maintainable way.

Happy routing!
Maria

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