Re: [isp-bgp] BGP over multihop ethernet best practices?

[Darrell Hyde <dhyde@...>]

> transitA >ethernet> switch1 >ethernet for 200 miles> switch2 >ethernet>
> router1

I use managed long-haul transport for a number of my transit links, so I
deal with just this scenario pretty frequently.

The biggest downside is that if line protocol on your long-haul (ZX w/
regen I'm assuming) circuit fails, the routers at either won't know
because they establish line protocol with their adjoining interfaces on
either end. This can be problematic because it means you have to tune
your BGP timers to kill off the session pretty quickly if you start
missing hellos. I usually set my hello interval to 5 seconds, and set my
dead timer to 45 seconds. That's significantly faster than the default
BGP timers, quick enough that it mitigates the impact, and not so short
that you run into flapping scenarios.

Canoga Perkins makes a nice media converter that supports link loss
carry forwarding and could replace the switches in your equation to fix
that problem. In essence the routers at either end would establish line
protocol with one another which would allow for your BGP session to be
torn down immediately if any portion of the link were to fail.

While this gets you around the initial problem, its still not my
favorite way to receive transport. I generally prefer to light both ends
myself whenever possible.

D.





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