Traffic per Prefix Length

Wed May 23 00:31:05 UTC 2001

>>>>> "bw" == Bill Woodcock <woody at zocalo.net> writes:
>> does anyone collect stats that would facilitate the derivation of
>> the number of packets forwarded per prefix length (per unit time)
>> in the routing table or per prefix length range?

> Anybody who's doing both Netflow and BGP table dumps can do that.
> Of course, the corellation between the two isn't perfect, since you
> may have prefix-length changes between snapshots.

Another possibility would be to use one of the bucket-based accounting
mechanisms (BGP Policy Accounting on Cisco and Riverstone, Destination
Class Usage on Juniper):

* define a route-map which maps announcements with different prefix
  lengths into different buckets

* have the interfaces count traffic towards prefixes in each bucket
  automagically.

The current Cisco implementation only has 8 buckets, which is a bit
low because there are more than 8 prefix lengths in the real world.
Juniper has 16 buckets which looks much better, and Riverstone has 25
which would cover even the absurd cases.

Randy: You could also use this mechanism to count traffic that would
potentially be affected by various kinds of route filters (by
assigning a bucket instead of actually dropping the announcements).

Some pointers to these features can be found on

http://www.switch.ch/misc/leinen/snmp/monitoring/bucket-accounting.html
-- 
Simon.