[c-nsp] OSPF link costs

[Robert Blayzor]

Bruce Pinsky wrote:
> Are S1 and S2 a layer 3 hop or not?  From your description, I'm guessing
> not if you say there is only a single SVI between the routers.  That

They are an L3 hop, both switches have an SVI into the same VLAN/subnet.
 Actually both switches have two different VLAN's/SVI's.  Router R3 and
R4 have two links upstream.  Both S1 & S2 have SVI's for example, VLAN5
and VLAN10.  Both R3 and R4 have one each links in VLAN5 and VLAN10, and
SVI exists for each VLAN on each switch. (two SVI's per switch).  Equal
cost hops to R3 and R4 don't seem to be a problem, but R4 has one link
which is only 100M, which I'd only want to be used should the GE link
not be available.

> Minimally, to deal with this you need to have 2 SVIs on the S1 and S2
> devices.  That way you can adjust the cost of the SVI between S2 and R3/R4
> to reflect the fact that there is a GE/FE rather than a GE/GE connection in
> that path.
> 
> Ideally there would be three SVIs so that the links between the devices can
> be given individual L3 costing info.  The bottom line is that you get one
> L3 cost per L3 domain/subnet.

That's what I'm figuring, but I didn't know if there was a possible way
to set the metric upstream, via some sort of preference, so that the
100M link on R4 is not used.  Seems like the only way is to create
another VLAN with L3 interface setting a higher cost facing the
downstream routers.  (I wanted to try to avoid that)

-- 
Robert Blayzor, BOFH
INOC, LLC
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