[Olsr-dev] Multipath routing in OLSRD

ZioPRoTo (Saverio Proto) (spam-protected)
Tue Mar 3 20:56:07 CET 2009

> But when you want to move traffic on the "second shortest path" (as an
> example) the next node a will route it differently, because "second
> shortest path might not be the same for this node (even if you mark your
> package so the next hop will know that this is "second shortest path"
> traffic).
> I know someone who "solved" this problem with source routing... but it's not
> very efficient to explicitly set every hop of the route into the IP packet (or
> some container format).

The key point here is that the routing decision is taken at each hop,
but you want to force the traffic into a path choosen by the first hop

There are two ways theoretically to solve this problem

Once the source node computes the "second shortest path" to a
destination and you want your traffic to go on that path you can:

1) Keep a state about the path on every hop of the path (do it with
some signalling)
2) Make IP packets carry information about the path (source routing)

both solutions permit to do the right thing at the time of routing
decision at each hop.

IP packets support natively source routing (look RFC 791 loose source
routing and strict source routing) but if I remeber right there are
some limitations.
For example all router must honor the source routing option and the
number of hops you can specify is limited (maybe it was 8 hops).

I have been working and thinking on similar topics recently, so if you
have any doubt feel free to ask.


Saverio Proto

PS you may find interesting stuff on source routing reading the
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