[c-nsp] HSRP and BGP

[Trent Lloyd]

0Howdy,

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matt carter wrote:
>
> speaking at least from a domestic point of view, most nsps are happy enough
> to allocate a /29 instead of a /30 for the interconnect subnet but aren't
> too happy about running dual layer 3 bgp peers on a single layer 2
> connection. ( mainly i think because it seems to throw all their support &
> diagnostics processes out the window having 2 sets of peers on 1 link ) ...
> in my experience, the standard response to this kind of request is to the
> effect of if you want n+1 get a second link and do it properly at both
> layer2 and layer3, which for whatever reason, simply may not be cost
> justifiable.. in that scenario, id opt for something is always better than
> nothing.. ( how receptive are nsps in other countries to this 1 xconnect w/
> 2 sets of peers kind of request? )
>   
Here in Perth, at a small level ( < 100Mbit of transit), we had 1 
upstream that was unwilling to allocate a /29 (/30 only), nor run a 
second BGP session unless we purchased a second link.  Additionally 
their standard policy was that their links MUST be terminated on a L3 
device and not on a L2 device, although they were a little more flexible 
on that one. 

Running HSRP/VRRP/etc over a /30 on Cisco seems dodgy at best, however 
there is 1 method I have found that seems to work (using a private 
subnet, the primary virtual also on that subnet, having a secondary 
virtual inside the /30, and a route for the subnet directly out the 
interface) -- I did not use this in production so can't comment on if 
that would work for you, all the other issues with BGP session timeouts, 
etc aside.

However, our new upstream was happy letting us use a /29 and having 2 
BGP sessions -- we are using MEDs rather than prepends.

Good option for a bit of extra redundancy if for whatever reason your 
situation allows for having 2 border routers, but only 1 upstream provider.

Cheers,
Trent

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