[c-nsp] downlink bgp interconnect best practices

[Gert Doering]

Hi,

On Tue, May 31, 2011 at 10:10:14AM -0500, Pete Templin wrote:
> Having "learned" in a multi-pop environment, I learned to separate into 
> three groupings: "edge" routers for upstream transit/peer connections, 
> "distribution" for downstream customer connections, and "core" as the 
> glue that holds everything together.  

Yeah, I agree.  Right now, this doesn't make sense in our network setup
(and the extra routers cost money :) ) but in general, yes.

> Lots of little reasons why:
> 
> If another city's WAN link comes into CR1 and you have an uplink there, 
> that city's outbound traffic will want to leave via the uplink there 
> unless you really motivate BGP to punt the traffic to CR2.  In other 
> words, if BGP doesn't make a decision before step 9 (Prefer the external 
> BGP path over the internal BGP path), all of your traffic arriving on 
> CR1 is leaving by CR1's upstream(s).

We do mostly "hot-potato" routing, that is: if local-pref, path-length
and med are all the same, just send out the nearest upstream / peering
point.

Which would do the right thing in that case :-) - but if your policy
is different, it won't.

gert
-- 
USENET is *not* the non-clickable part of WWW!
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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