OSPFv3: link-local address required on loopback interface?

[Ondrej Zajicek]

On Tue, Aug 28, 2012 at 03:08:00PM +0200, Tore Anderson wrote:
> I've run across a rather weird behaviour in BIRD 1.3.8 regarding the
> interaction between address(es) on the loopback interface and the OSPFv3
> protocol. It seems that if there's no link-local address on the
> interface, BIRD fails to run OSPF in stub mode on it:
...
> 
> Question: What does ?Ignored? imply here?

That it is loopback and should not be used for active ifaces.
But stub ifaces should be OK.

> Also, why did the ?Primary? address change as a result of fe80:: being added?

This is a bug in primary address selection.

> In any case, this means that without a link-local address being manually
> added to the loopback interface, the primary address of the router won't
> be reachable from the rest of the network, in turn causing problems for
> monitoring and possibly other protocols like iBGP.
> 
> This must be a bug, right? Being able to import the loopback interface
> of a router as a stub network into the IGP is pretty fundamental
> functionality. Also, link-local addresses aren't typically seen on
> loopback interfaces, so expecting them to be there doesn't make much
> sense to me.

OSPFv3 requires link-local address on iface to work, so there is just 
a missing exception for stub ifaces.

Also note that some people suggest to use dummy iface instead of loopback
iface for that purpose. But i don't know any valid reason why. Perhaps
just to workaround similar issues in other software.

-- 
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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