The Cidr Report

Sean M. Doran smd at
Tue Aug 18 10:25:03 UTC 1998

Tli asked:

| Exercise for the reader: If prefixes of length F and longer are filtered,
| and a domain has a prefix of length N, how many prefixes can they propagate
| into the backbone?  How many before people start proxy aggregating them?

A/      (2 ** F) - 1.   [assuming nobody imposes exact-match prefix filters]

B/      When we can easily do:

	"router bgp N
         proxy-aggregate route-map Lazy-Types

	! exceptions
	route-map Lazy-Types deny 10
        match as-path 100

	! the rule
	route-map Lazy-Types permit 20
	match originated-prefix-count 16"
	then the number 16 strikes me as a starting point,
	although I probably want to re-read Dennis's comments
	from a few years ago.

Do I pass?


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