[c-nsp] BGP Multipath and unequal IGP metrics

[David Hughes]

Hi

I have a situation that looks like a problem in the making.  In a  
subset of our network there's a pair of well connected datacentres (eg  
dual 10GE paths etc).  One of our upstreams will shortly be presenting  
a transit path at both of these 2 locations.  No problems I think to  
myself - we'll just multi-path from our core and load share over both  
paths.

Problem.  Seeing as the 2 border routers in question are at different  
locations, the core routers see different IGP metrics to the nexthop  
of the BGP table entry.  As a result they are excluded from use with  
BGP multipath and I'm left with the core routers at each DC only using  
the paths to the border router at the local site.

I don't want to mess around with tweaking the OSPF metrics as I'm sure  
that's just a disaster waiting to happen for some poor network  
engineer in a year or two.  I thought I'd found a nice clean solution  
with Cisco's "multipath unequal-cost" feature but for some reason I  
can't even start to understand you can only use it in a VRF, not in  
the default table.

So the only solution I can see is to reconfigure the core devices and  
move all interfaces and routing processes into a VRF so that I can  
effectively get this feature on our entire table.

What am I missing here?  Surely I'm not Robinson Crusoe - someone must  
have done this before.  Platform is Cat6k / Sup720.


Thanks

David
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