AOL & Cogent

Stephen J. Wilcox steve at
Mon Dec 30 19:52:32 UTC 2002

On 30 Dec 2002, Jeff S Wheeler wrote:

> On Mon, 2002-12-30 at 06:37, Basil Kruglov wrote:
> > For my not-so-bright customers I simply want traceroutes to look good when
> > they run one from Level3-homed site. Obviously a ~5-7 hops to us looks
> > really disturbing, try to explain to one of them that there is no problem.
> After some off-list discussion I think I understand the issue.  You do
> not want customers who are doing a traceroute from Level3 or one of
> their downstreams to see high latency on some of their traceroute hops
> going toward you, because you cannot control the egress path of those
> ttl_exceeded packets from cogent's network, even though you can control
> your own egress.
> So the obvious solution is to prepend your advertisements toward cogent,
> which will cause them to carry less of your inbound traffic.  This has a
> negative impact for cogent, because they need that inbound traffic to
> justify some of their peering agreements (think, ratios).  Supposedly
> this is the reason they couldn't keep the ATDN peering, eh?  If all
> their web host-type customers suddenly start prepending advertisements,
> it will cause them to bleed inbound traffic.

This doesnt work well for two reasons.

One is that as path is fairly low down on the path selection and easily
overridden by other factors eg localpref

The other is that if the network is providing transit then you want to avoid
prepending as you will most likely reduce your transit revenue.


> If you want to encourage cogent to build a rich community set so you can
> prepend only toward Level3, perhaps you should start prepending toward
> cogent and make the point with your cogent rep that this is going to
> cause them to lose your inbound traffic, and if they gave you more
> control over route advertisements, it would not have such an impact.
> On the other hand, maybe cogent doesn't want web hosts as customers. :-)
> --
> Jeff S Wheeler <jsw at>

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