[c-nsp] BGP routes co-existing with different local-preference

[David J. Hughes]

> An alternative to session timer tweaking is running a version that  
> supports
> BGP Next Hop Tracking and having your next hops propogated in your IGP.
> Then a box failure or intermediate path failure that results in your  
> next
> hop becoming unreachable will cause the removal of routes that use that
> next hop in just over the time it takes your IGP to converge and  
> result in
> the triggering of best path selection for those routes.
>
> http://www.cisco.com/en/US/products/ps6350/ 
> products_configuration_guide_chapter09186a008045561e.html


Yup, nice step forward for some situations.  Correct me if I'm wrong,  
but it doesn't help your session to a router if that router is reached  
via ethernet and there's a switch between them.  You will always think  
you are directly connected so there's a valid next hop even when the  
box has fallen over.  Other than using BGP's timers or BFD if/when it  
becomes commonly deployed, I can't see a way to detect a silent peer  
failure.  I doubt BFD is ever going to be an option between AS'es so  
timers look like the only option to an eBGP neighbor.


David
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