Babel in Bird

[Ondrej Zajicek]

On Thu, May 05, 2016 at 03:02:55PM +0200, Juliusz Chroboczek wrote:
> What you describe is perfectly correct.
> 
> > 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?
> 
> It's worse than that, actually -- it's not the route timeout, it's the
> source GC time.

Yes, you are right, i missed this.


> The issue is a consequence of having a stateful loop-avoidance algorithm:
> if the state is lost, the loop-avoidance algorithm gets confused, and only
> recovers after the state has expired.
> 
> Babeld currently has two workarounds:
> 
>   - it stores the current seqno on disk when it shuts down, so that it can
>     use the same seqno when it restarts;
>   - it can optionally draw a random router-id at startup, so that the old
>     and new states don't interfere.
> 
> It would be great to design a procedure to recover from this case without
> a timeout, but I haven't given it much thought yet.  So for now consider
> it as a flaw in the protocol.

Using random router-id seems like a good idea. Perhaps even an TLV that
describes 'nominal' configured router-id, so regular router-id could be
random, but routes could still contain configured router-id for admin
purposes. Unfortunately, Babel does not have support for something
like Opaque-LSA.

Could not help with this issue just to allow increasing seqnum by more
than 1 in reaction to recevied seqno request (3.8.1.2), to value
rcv_seqno+1 ?

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."