Peering Exchange Configurations

Joe Abley jabley at hopcount.ca
Thu Apr 8 11:47:45 CDT 2010


On 2010-04-08, at 12:42, Elmar K. Bins wrote:

> jabley at hopcount.ca (Joe Abley) wrote:
> 
>>> 1) Is a private AS typically used for the exchange side of the session?
>> No. Also many exchange points do not run route servers at all, and expect participants to build bilateral BGP sessions directly between each other.
> 
> ...which is a shame. Routeservers in place gives you a nice benefit
> upon hooking up to the exchange and before you have even found out
> who is on the grid (anyone have a list for NOTA?).

I've never had a problem getting a participant list for NOTA from Terremark.

One down-side of route servers on a shared exchange fabric is that the layer-2 path through the exchange for the BGP sessions does not always match the layer-2 path through the exchange for traffic. This means that AS1 might continue to learn AS2's routes through the route server even though there's a layer-2 problem that prevents AS1 and AS2's peering routers from talking directly to each other. Hilarity may result.

I've never seen such a problem on small exchanges where the layer-2 fabric is simple, but I have seen it more than once on larger, more complicated exchanges.

My personal preference is to focus peering energy on bilats, and not to rely on a route server. But I understand the savings in opex that route servers can provide on busy exchanges.


Joe





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