advertise OSPF default route into a specific area?
hello, i'm using BIRD 2.16.1 on FreeBSD 15.0. 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? please feel free to let me know if this is a bad idea or if i'm using OSPF wrong :-) thanks, lexi.
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. Have a nice weekend! Maria -- Maria Matejka (she/her) | BIRD Team Leader | CZ.NIC, z.s.p.o.
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: santiago@crfreenet.org) "To err is human -- to blame it on a computer is even more so."
Maria Matejka:
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.
thanks Maria and Ondrej, after thinking about this, i agree it probably makes more sense to run EBGP between these networks rather than OSPF. so, i'm doing that now and everything is working fine :-) regards, lexi.
participants (3)
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Lexi Winter -
Maria Matejka -
Ondrej Zajicek