Babel in Bird

[Ondrej Zajicek]

On Mon, May 02, 2016 at 03:59:35PM +0200, Toke Høiland-Jørgensen wrote:
> Ondrej Zajicek <santiago at crfreenet.org> writes:
> 
> > I have two questions w.r.t. this sequence of events:
> >
> > 1) How is router restart and seqnos supposed to be handled without
> > waiting for route timeout?
> 
> This is indeed a problem. Babeld sends a wildcard retraction before
> shutting down (which I just taught Bird to handle; will send off the
> patch tonight after testing it properly). I can add in sending such
> retractions when an interface goes away as well.
> 
> But this problem can still occur on a crash, or if the retraction was
> lost for whatever reason. In that case, waiting for things to expire is
> the only option.

Perhaps sending wildcard retraction not only in the last packet, but also
in the first one?


> > 2) If a route is selected, then becomes unreachable/retracted, and
> > there is no other route to be selected, is it still considered
> > selected? I would say that no as the selection process (3.6) forbids
> > retracted routes to be selected, but the BIRD implementation keeps the
> > old selected route (now unreachable) in this case.
> 
> It is kept for a while (and installed as unreachable) to avoid transient
> routing loops. This is described in section 2.8 of the RFC.

Well, section 2.8 (and in more detail section 3.5.5) specifies that we
should keep unreachable entries, but IMHO it does not specify that the
old route is considered selected/installed for a purpose of conditions in
section 3.5.4. The unreachable entry after retraction could be undestood
as a special case, unrelated to any route.


-- 
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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