Internet routing table "completeness" monitoring?

Wed Oct 3 13:50:50 UTC 2012

I have cacti graph the amount of prefixes announced and withdrawn from a BGP peer on each BGP router.

-----Original Message-----
From: ML [mailto:ml at kenweb.org] 
Sent: Tuesday, October 02, 2012 11:43 PM
To: North American Networking and Offtopic Gripes List
Subject: Internet routing table "completeness" monitoring?

Has anyone put in place a method to identify if one their BGP peers suddenly withdraws X% of their prefixes?

e.g I should expect ~420k prefixes in a "complete"[1] routing table from a transit peer today.  If suddenly I'm only getting 390k prefixes I'd guess a major network was depeered or similiar.

If so how are people doing this? SNMP MIB, screen scrape?

[1] Varying levels of completeless apply.