[Nanog] Cogent Router dropping packets

Joe Greco jgreco at ns.sol.net
Mon Apr 21 14:54:40 CDT 2008

> Joe Greco wrote:
> > For those unfamiliar, Cogent has a system where you set up an EBGP peering
> > with the Cogent router you're connected to, for the purposes of announcing
> > your routes into Cogent.  However, these are typically smaller, aggregation
> > class routers, and do not handle full tables - so you don't get your routes
> > from that router.  To get a full table FROM Cogent, you need to set up an
> > EBGP multihop session with them, to their nearest full-table router.  I 
> > believe they actually do all their BGP connections in that manner.
> Depends on the service you purchase. Fast Ethernet seems to be delivered 
> as eBGP-multihop (the first hop is just a L3 switch), however DS-3 is 
> handled as a single BGP session. I'm not sure if GigE or SONET services 
> are handled as multihop or not.

GigE is, though perhaps not in all cases (we had a client buying x00Mbps
delivered over gigE, which was definitely multihop).

> Probably all depends what hardware they have at each POP....

In part, I'm sure.  There is also a certain benefit to having consistency
throughout your network, and it sometimes struck me that many of the folks
working for Cogent had a bit more than average difficulty dealing with the
unusual situation.  This is not meant harshly, btw.  Generally I like the 
Cogent folks, but they (and their products) have their faults, just as any
of the competition does.

It may also help to remember that there's "legacy" Cogent and then there's 
PSI/etc.  Perhaps there are some differences as a result.

The more things you can do using the same template, the less difficult it
is to support.  On the flip side, the less flexible you are ...

... JG
Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net
"We call it the 'one bite at the apple' rule. Give me one chance [and] then I
won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN)
With 24 million small businesses in the US alone, that's way too many apples.

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