On Sat, Feb 22, 2025 at 03:13:28PM +0100, Maria Matejka via Bird-users wrote: > Hello Lexi, > > On Sat, Feb 22, 2025 at 01:34:51PM +0000, Lexi Winter wrote: > > > i have an OSPF ABR in area 0 and area 1. this router has a default > > route via a non-OSPF interface (kernel route, imported into BIRD using > > the 'kernel' protocol). i'd like to advertise this route into area 1, > > but *not* into area 0. > > > > how would i go about doing that? > > I would filter out the default route on all the area 0 routers. > > > please feel free to let me know if this is a bad idea or if i'm using > > OSPF wrong :-) > > Well, OSPF isn't intended for filtering routes between areas this way. > Guessing from what you have written, it may make sense e.g. to run one > OSPF instance per area, assign each area a BGP private ASN and run BGP > between them.
If the area 1 is NSSA, it is possible to filter out external routes that are propagated from NSSA area to backbone using 'external' option: https://bird.network.cz/?get_doc&v=20&f=bird-6.html#ospf-external It works in a similar way how 'networks' option can be used to filter internal routes: https://bird.network.cz/?get_doc&v=20&f=bird-6.html#ospf-networks It could be interesting to replace / augment this with BIRD filter language. The issue here is that if the external route is originated on ABR, it could either generate NSSA-LSA in the NSSA area, or just regular Ext-LSA in backbone area. That is something that perhaps should be configurable, but i think we always generate Ext-LSA on ABRs. -- Elen sila lumenn' omentielvo Ondrej 'Santiago' Zajicek (email: santi...@crfreenet.org) "To err is human -- to blame it on a computer is even more so."
