Pointers please - OSPFv3 vs Cisco IOS XR

[Ondrej Zajicek]

On Sun, Jul 05, 2020 at 11:56:45AM +0200, Elmar K. Bins wrote:
> G'day all,
> 
> we were able to solve the problem today (thanks to my ingenious colleague).
> 
> In IOS XR, Cisco supports multiprotocol SNMPv3 and thus sets the bits correctly
> for this. BIRD flukes on it. We got a lot of "I-bit mismatch(7)" messages.
> 
> Disabling rfc5838 support does the trick for us, since we're running ospf2 for
> IPv4 and ospf3 for IPv6 (because...old IOS boxes in the mix in other places...)
> 
>     rfc5838 no;
> 
> My colleague supports the idea that this might be a bug in BIRD; if you need
> debugging output to help, please ping me.

Hi

This should not matter. If rfc5838 option is enabled (by default) and
instance 0 is used (by default), then only thing this does is to signal
RFC 5838 support by having AF-bit flag set in Hello and Dbdes packets.

Perhaps it is some bug in old IOS that rejects (instead of ignoring)
unknown option flags?

If i remember correctly, it is Cisco side who resets session back to
initial state (so there is I-bit mismatch).


> > > Do not see any issues on BIRD side. It seems to me that Cisco just resets
> > > the exchange (by sending DBD flag I) when it should be done (or in Loading
> > > state):
> >
> > I could not find any trace on the XR side, but I'll continue digging. I did
> > actually expect it to be an MTU issue, but could find no proof of that. I
> > also don't understand why OSPFv2 would work, but OSPFv3 would not.
> >
> > > I suppose that this exchage repeats indefinetly and 'show ospf neighbors'
> > > on BIRD also shows the other side in ExStart/Exchange?
> >
> > Actually, the routers show as ExStart/DR and ExStart/BDR, which is also strange.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at 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."
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