Known communities for AS174?

Adam Rothschild asr+nanog at
Tue Mar 22 19:52:20 UTC 2005

On 2005-03-22-03:30:32, David Hubbard <dhubbard at> wrote:
>   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 out of date or maybe has something else to try?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

      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 at
and request an updated list.

Hope this helps,

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