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? percentages would
work too.
Interesting ... Do you think that this will give you any useful information?
I would be more interested in how far packets go. Not in networks terms but
in real distance. Next would be to go further up the stack and see if there
is a difference in protocols (i.e www compared to dns).
-- Arnold
There are many interesting pieces of data and there is plenty of data
in the Internet to collect. 
might show how much work routers have to do in particular areas of the
table (which, granted, varies from location to location) when doing
longest-prefix match. what areas of the table are hit more than others.
"sh ip cef traffic prefix"
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.
-Bill
Interesting ... Do you think that this will give you any useful
information?
I would be more interested in how far packets go. Not in networks
terms but
in real distance. Next would be to go further up the stack and
see if there
is a difference in protocols (i.e www compared to dns).-- Arnold
Actually, I had some interest in this same information. One thing I was
thinking about is some routers that don't have the memory to hold a full BGP
table. They need a default route for traffic to blocks not in their tables,
but it would be interesting to work out an optimized filter to decide which
routes to send them. One theory is to send them the routes to the largest
blocks in the hopes that these will tend to get you the most packets for the
routing table byte.
DS
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