Hello, I'm looking for a way to do path prepending
for my prefix as it leaves AS174 (Cogent), one of my
upstreams. The following:
http://www.radb.net/cgi-bin/radb/whois.cgi?obj=AS174
suggests that at least as recently as last May they
might have accepted:
3. Communities controlling Cogents AS path prepending
for customer routes on egress:
community effect
174:3000 do not announce
174:3001 prepend 174 1 time
174:3002 prepend 174 2 times
174:3003 prepend 174 3 times
But I've tried setting each of those and it doesn't
seem to have any effect. Anyone know if that info is
out of date or maybe has something else to try?
Thanks,
David
dhubbard@dino.hostasaurus.com (David Hubbard) wrote:
But I've tried setting each of those and it doesn't
seem to have any effect. Anyone know if that info is
out of date or maybe has something else to try?
Are you sure you're sending communities?
Elmar.
[...]
3. Communities controlling Cogents AS path prepending
for customer routes on egress:
community effect
174:3000 do not announce
174:3001 prepend 174 1 time
174:3002 prepend 174 2 times
174:3003 prepend 174 3 times
But I've tried setting each of those and it doesn't
seem to have any effect. Anyone know if that info is
out of date or maybe has something else to try?
I'm of the understanding that Cogent supports the following BGP
communities (and no others):
174:990 - This community makes sure that the customer's route
does not leave the Cogent AS of 16631. What this
means is that if a peering partner or BGP customer
of Cogent is trying to send traffic to this route,
the peering partner or BGP customer of Cogent will
not see this route from Cogent, and will therefore
not send packets for that destination to the Cogent
network.
174:991 - This community makes sure that the customer's routes
are not passed on to Cogent's peering or transit
partners, but are sent to Cogent's BGP
customers. Almost the same situation as 16631:990,
except that BGP customers of Cogent will see the
route, and will have the option of sending those
packets via Cogent.
174:10,95,100,105,110 - Each of these communities sets a
different local preference on a
customer's routes. A detailed
explanation of what these are is
beyond the scope of this
document. However, 16631:10 will have
the effect that even inside the Cogent
network, the Cogent network will
prefer any other path seen as best
before using the customer's line. This
could be used, for example, if a
customer has a line with another ISP,
and wants to never use the Cogent line
for traffic (even from Cogent itself)
except when the other line is down.
With that said, your best bet might be to contact support@cogentco.com
and request an updated list.
Hope this helps,
-a
[ snip ]
Not a Cogent customer, but they have a list of supported communities in
the comments for the RIPE RR entry for AS174 (which seems to have been
updated fairly recently). The communities shown in the original post
also show up there.
w