[Xorp-users] wanted: OSPF metrics per neighbor. can vif help?

[Kristian Larsson]

On Wed, Nov 09, 2005 at 07:29:41PM -0500, Nick Feamster wrote:
> Atanu,
> 
> Thanks for the quick, clear reply.   A few comments inline...
> 
> On Wed, Nov 09, 2005 at 03:58:13PM -0800, Atanu Ghosh wrote:
> > The interface-cost is a per interface setting and it was a mistake in
> > the template file to require it to be set at the address level. It
> > should be set at the interface level with the link-type.
> 
> That makes sense.  Is this fixed in the current CVS version of XORP? 
No.
> > In the OSPF implementation the interface and vif are combined to form a
> > PeerOut (which is the equivalent of an OSPF interface). The PeerOut is
> > where the interface-cost is stored.
> 
> I guess I am confused as to the point of the vif.  It isn't really
> explained in the user's manual.  Why have it at all if I can't create
> multiple virtual interfaces with different names on top of a single
> phyiscal interface?
The genereal idea is to be able to create for
example VLAN interfaces though the code is not
there yet.
> 
> > At the moment the FEA enforces that the interface and vif name are the
> > same. Which is why you haven't been able to change the vif name. There
> > have been some discussions on this issue over the last few days on
> > xorp-hackers.
> > 
> > If you can create a separate tap device per neighbour then you will be
> > able to set the interface cost with the current code.
> 
> This option presently does not exist, so we are looking for workarounds.
> 
> > The other option is add code to take the interface cost per neigbour in
> > a similar manor to the way that the neighbour router-id is
> > configured. If you make a bugzilla entry requesting the enhancement and
> > upload the patch that would be useful.
> > 
> > >From my reading of the specification all links from a particular
> > interface should all have the same link cost.
> > 
> > ---------------------------------------- RFC 2328
> > 		o   For each fully adjacent neighbor associated with the
> > 		    interface, add an additional Type 1 link (point-to-
> > 		    point) with Link ID set to the Router ID of the
> > 		    neighboring router, Link Data set to the IP
> > 		    interface address and cost equal to the interface's
> > 		    configured output cost.
> > ----------------------------------------
> > 
> > We would be slightly concerned about adding code that may violate the
> > standard, however, this seems like a useful feature.
> 
> I understand what the RFC says, and sticking to standards seems like a
> good idea in general.  If I could create multiple virtual interfaces
> (vifs) on top of a single phyiscal interface (e.g., one vif per
> neighbor) and subsequently set the interface cost per vif, then would
> that not comply with the standard and give me the functionality we
> want/need?
Even if you could create several interfaces it
would not do you much good. How would you separate
the traffic between the interfaces?
I beleive it to be very difficult.

   Kristian.
> Cheers,
> Nick
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