RIR filtering & Level3

Thu Nov 15 14:20:58 UTC 2007

> Are any other L3 customers seeing the large number of /25 and smaller 
> routes from L3?  I'm seeing almost 2500 of these routes in 
> 4/8, some but 
> not as many in 8/8 and still more in L3's non-US allocations. 

I am pretty sure that L3 allows anything up to a /28 (they used to,
anyway, from my old notes on their policy) on customer peering sessions.
It may be /25 now.  Non-peering sessions explicitly disallow anything
longer than a /24, according to 'whois -h whois.radb.net as3356':

remarks:        The following import actions are common to every
remarks:        Level 3 non-customer peering session:
...
remarks:        - Prefixes shorter than /8 or longer than /24 are
remarks:        not announced.

Global Crossing does the same, as do many other providers.  Best thing
is to just deny anything longer than /24 at your border if you do not
have multiple egress points to this one provider.  To be sure they are
customers, check the community string to see if it is 3356:123.

-evt