[c-nsp] BGP Multipath and unequal IGP metrics

[David Hughes]

Hi

Hate to bump my own post but does anyone have any thoughts on the below?


Thanks

David
...

On 28/07/2009, at 10:11 AM, David Hughes wrote:

> 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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