North American Network Operators Group

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RE: Pitfalls of _accepting_ /24s

  • From: Howard C. Berkowitz
  • Date: Thu Oct 16 21:06:37 2003


A proposal was made some years ago, which I thought was by Tony Li, but, IIRC, he says it wasn't original with him. It does require cooperation from competitors, but can reduce the number of announcements. Under some circumstances, it may cause blackholing, but so can /24 filtering.

The idea is to establish bilateral blocks of provider space. Let us say Provider A and Provider B recognize that they have a significant number of common multihomed customers. Arbitrarily, one of the providers (assume A) starts off with a block -- let's say a /19 or /20 to which both providers will assign their multihomed customers. A and B peer and send more-specifics to each other.

To the outside world, however, A advertises its largest aggregate plus the multihomed block. B advertises this block of Provider A space as well as its own aggregates.

If A and B do not peer, the likelihood of blackholes become much higher since they may not see the more-specifics in the multihomed block.

Has anyone reexamined this proposal lately?