[Olsr-dev] Patch Orgy Syncup

[Juliusz Chroboczek]

> | > b) Small Hysteresis on HNA4 0/0 to prevent routing flaps especially
> | >    when ETX(a) slowly grows and ETX(b) slowly shrinks there is a 5
> | >    minute "flaptime" for such a route.

> | Could you describe how that works?  I'm worried it might create
> | routing loops.

> i share your concerns - there is one other protocol which uses
> kind damping tequnique which is BGP. for exactly the same reason
> (routing loops) it is prohibited to damp internal paths ...

It's slightly different.  BGP is a hierarchical protocol, and the
prohibition of intra-AS flap damping is due to the requirement for
routes to be consistent within the AS.

This doesn't apply to OLSR, which is a flat protocol.  The problem is
that OLSR is a link-state protocol, and such protocols absolutely
require that topology information and path computation be consistent
across the routing domain.  So hysteresis for link costs should be
okay (as long as everyone has the same idea of a given link cost), but
hysteresis on shortest path computation will break.  But I'm not
excluding that Sven-Ola is doing something smart to work around the
problem.

(OSPF partly works around the issue by using hierarchical routing, but
I doubt that's what Sven-Ola is doing.)

> one of the things what we would like to do for olsr-ng is
> to work on that problem too - rather than damping routes
> we'd like to to setup a GRE tunnel to the node offering the 0/0
> route.

> now "stickyness" to a certain default gw is easy and does not
> create routing loops.

Yes, that should work.  Although my personal preference would be to
use a protocol that is robust in the face of inconsistent information.

That's getting off-topic for this list -- is there a better place to
discuss it (in English)?

                                        Juliusz