BGP Filtering

Ben Butler ben.butler at c2internet.net
Tue Jan 15 16:11:36 UTC 2008


Hi,

Considering:

http://thyme.apnic.net

Total number of prefixes smaller than registry allocations:      113220
!!!!!

/20:17046   /21:16106   /22:20178   /23:21229   /24:126450

That is saying to me that a significant number of these smaller prefixes
are due to de-aggregation of PA and not PI announcements.

My question is - how can I construct a filter / route map that will
filter out any more specific prefixes where a less specific one exists
in the BGP table.

If my above conclusion is correct a significant portion ~47% of the
number of the prefixes in the table could be argued to be very
unnecessary at one level or another.

Is such a filter possible easily or would it have to be explicitly
declared, any chance of a process the automatically tracks and publishes
a list of offending specifics similar to Team Cymru's Bogon BGP feed.

As a transit consumer - why would I want to carry all this cr*p in my
routing table, I would still be getting a BGP route to the larger prefix
anyway - let my transit feeds sort out which route they use & traffic
engineering.

Thoughts anyone? 


Kind Regards

Ben



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