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Re: Traffic per Prefix Length
From: Simon Leinen <simon () limmat switch ch>
Date: 23 May 2001 02:31:05 +0200


"bw" == Bill Woodcock <woody () 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.


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