[Ns-bugs] [Bug 406] GlobalRouteManager behaviour after Ipv4 interface SetDown and SetUp procedure

[code@nsnam.ece.gatech.edu]

http://www.nsnam.org/bugzilla/show_bug.cgi?id=406





--- Comment #12 from Tom Henderson <tomh at tomh.org>  2008-11-15 17:45:13 EDT ---
(In reply to comment #9)
> (In reply to comment #6)
> > > 
> > > Attached is a patch that we used. I am not sure how sound this strategy is?
> > > 
> > > However, this does not help with the case where there are multiple paths
> > > between a source destination pair. When one of the paths becomes unavailable,
> > > we are not able to make the simulator use the alternative path with the global
> > > routing manager.
> > > 
> > 
> > The reason the patch will not completely work is that it doesn't delete the
> > existing routes.  Try adding a loop that deletes everything first, before
> > reinitializing things.
> > 
> > for (uint32_t i = 0; i < ipv4->GetNRoutes(); i++)
> >   {
> >     ipv4->RemoveRoute (i)
> >   }
> > 
> 
> We have couple of questions:
> 
> 1-I am not sure where to implement above code partly due to lack of complete
> picture of GlobalRouting implementation. 

For some basic overview material, see Section 9.9 of the manual:
http://www.nsnam.org/docs/release/manual.html#SEC100

>>> When one of the paths becomes unavailable,
> > > we are not able to make the simulator use the alternative path with the global
> > > routing manager.

The algorithm in the global routing manager is Dijkstra's SPF algorithm,
without equal-cost multipath.  So, there are no alternate paths that are
precomputed.  With the existing code (which was ported from quagga's OSPFv2
implementation) one would have to recompute routes whenever there is a topology
change or link change, to find an alternate route.

> 
> 2-Once the routes are removed, I guess we can rebuild the routes on all nodes
> with BuildGlobalRoutingDatabase () and InitializeRoutes () methods. Is this
> accurate?
> 

I believe so, but I haven't tested that in particular.


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