OSPF performance/SPF calculations

[Joakim Tjernlund]

Ondrej Zajicek <santiago at crfreenet.org> wrote on 2010/04/25 23:20:33:
>
> On Sun, Apr 25, 2010 at 06:08:04PM +0200, Joakim Tjernlund wrote:
> > > This is not a problem because both SPF and calc_next_hop() chooses the
> > > cheapest (full) ptp link. They both uses the same (local) metrics.
> >
> > Our ptp links typically have the same cost between the same two routers so
> > it is not unlikely that the link will be asymentric I think. However I
> > don't think that will be a problem anymore as BIRD don't use/support
> > equal cost multipath, right?
>
> Yes.
>
> > Right, how about these statements from RFC 2328:
> ...
> > These talk about inheriting ALL next hops from the parent and I don't
> > see the BIRD does that. Looks like BIRD just selects one next hop
> > from its parent?
> > Assuming it is, does that impose any restricts?
>
> Yes, BIRD chooses one next hop. Because BIRD does not implement equal
> cost multipath, this is not a problem.
>
> > Some other random questions:
> >
> > One think I always wanted is the possibility to add an host IP address to
> > all areas, in my case I like to export the routers primary IP address
> > to all areas so the router can always be reached. Is that possible with
> > BIRD?
>
> You can use 'stubnet' option to add 'virtual' stub network (in that case
> /32 stub) to the router-LSA. You can add this option to each area
> config to get this in each area.

That sounds exactly as what I need, thanks.

>
> Or add /32 stub network to one area, other areas get a summary-LSA
> with that address.
>
> > If you pull the cable to an ethernet I/F that is currently in a OSPF
> > domain, do BIRD delete the whole subnet from the R-LSA or do you
> > leave a host route with the I/F's IP address in the R-LSA?
>
> BIRD does not use link availability information, therefore if you pull
> the cable, BIRD keeps the whole subnet in the router-LSA (if it is
> a stub network).

If you do(any plans?), my vote is to leave a host stub in the R-LSA as it may
very well be possible to reach that IP address over another link.

 Jocke