[Nanog] Cogent Router dropping packets

manolo mhernand1 at comcast.net
Mon Apr 21 20:02:48 UTC 2008

I do have to say that the PSI net side of cogent is very good. We use 
them in Europe without many issues. I stay far away from the legacy 
cogent network in US.


Joe Greco wrote:
>> 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

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