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

[Nick Feamster]

On Thu, Nov 10, 2005 at 06:07:04PM +0100, Kristian Larsson wrote:
> You are going to do it in the kernel whether you
> like it or not. XORP merely instructs the kernel
> to set up another ip alias. Doing it via XORP is
> no different from doing it via ifconfig, iproute2
> or something else.

Actually, I am using click for the FEA, so I wouldn't necessarily have
to touch the kernel.

> However the example given above does not work.
> XORP does not seem to be able to handle alias
> interfaces such as eth0:1...

Exactly.  That's the problem I was running into.  One of them, anyway.
:)

> Vifs are as of today nothing more than internals
> to XORP, you can't actually do anything with them.
> You have to configure and can only configure _one_
> vif per interface and thus to allow what you are
> currently looking for ie setting cost per neighbor
> you would need several interfaces. This could be
> solved in at least two ways:
> 1. setup alias interfaces (eth0:1)
>  As described above, XORP unfortunately does not
>  support this :( so you're kinda down to:
> 2. one VLAN interface to each router
>  this is however a pain in the a** since you would
>  essentially have to full-mesh your ospf routers
>  if you wan't to be able to set cost on each.
> 
> you could always tunnel or do something with black
> magic... but basically you're full meshing with
> vlans or waiting for per-neihbor cost in xorp.

OK, great.  That's my understanding, too.  

> Why is it you want to set different costs per
> neighbor?

It's a pretty standard piece of functionality.  Typically, you want to set a
different cost for each edge in a graph: for example, my SF->LA link
should not have the same cost as my SF->NY link.  On a "real" router,
setting a cost per edge can be done by interface, since there is often a
different physical interface for each link (edge in the graph).  That,
of course, is not the case with XORP running on a PC.

Thanks very much for the explanations!

-Nick