RIR filtering & Level3
Eric Van Tol
eric at atlantech.net
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.
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