On Mon, Sep 28, 2015 at 08:58:35PM +0100, Israel G. Lugo wrote:
Hello,
I have a question regarding BIRD's OSPF and summarized networks. Not sure if I'm doing the right thing.
I've got access routers running BIRD, configured as ABR between area 0 and their respective user-facing areas.
Access networks are VLAN interfaces, e.g. eth0.161. Backbone connection is a separate physical interface (eth1).
If the physical access interface (eth0) goes link down for some reason, BIRD changes the VLAN OSPF interfaces (eth0.161) to Loopback state. It stops announcing the directly connected prefixes on the VLAN interfaces, but it keeps announcing a /32 for the interface's IP, with a metric of 0.
That in itself isn't the problem. It makes sense, as the IP belongs to the machine. The problem is, if I use the "network" option (to define summary LSAs), the /32 will be summarized to the entire prefix, making it be announced again. What's worse, it is now announced with a metric of 0, which means it will override any redundant routers I might have.
...
I understand that literally, BIRD is doing what I asked it to do: summarize A.B.C.0/24. As long as it has some valid route inside that prefix (in this case the /32), it will announce the whole summarized network, with a metric equal to the largest cost (RFC 2328, 12.4.3).
It would seem to me, though, that this case warrants special treatment. The /32 only exists because the interface transited to Loopback state when it lost the link.
Hello You are right with your analysis of the issue. I agree that in your case it does not make sense, but unfortunately, the behavior is IMHO more or less correct with regard to RFC 2328. I am not sure how it should be modified to be consistent and to make sense in your setting. /32 local definitely should be propagated (at least by default). Perhaps ignoring zero metric /32 from triggering summarization? Or ignoring any local stub network? Or some more general configurable limit for summarization (like minimal cost)?
Is there something I should be doing differently? Or could this perhaps be a bug, and not intended behavior?
Perhaps you could try to use stubnet option with hidden + summary suboptions to hide these /32 routes to not trigger the summary networks. -- Elen sila lumenn' omentielvo Ondrej 'Santiago' Zajicek (email: santiago@crfreenet.org) OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net) "To err is human -- to blame it on a computer is even more so."