I think the argument is not about route filtering - it is the implementation method.
Genuity uses ip extended access-lists.
Everyone else uses prefix-lists.
To a purist, the former is more granular, but performs poorly because it is a linked list implementation. The later, while less granular, performs faster by using a trie.
IOS 12.0S (and derivatives) are popular with ISPs (at least those who use Ciscos), and support 'access-list compiled', making access-lists likely to be around the same speed as prefix lists; they just take up RAM (one access list I use takes 10Mb of RAM once compiled). extended access lists still permit flexibility, ie, the /16 permitted only: access-list 111 permit ip host 192.168.0.0 host 255.255.0.0 becomes to permit all /16 thru /24 under that: access-list 111 permit ip 192.168.0.0 0.0.255.0 255.255.0.0 0.0.255.0 (might look less clear than a prefix list when you start wanting to let them permit say /19 thru /22, but then, router configs come from automated systems now, right? :-)) David. -- David Luyer Phone: +61 3 9674 7525 Network Development Manager P A C I F I C Fax: +61 3 9699 8693 Pacific Internet (Australia) I N T E R N E T Mobile: +61 4 1111 BYTE http://www.pacific.net.au/ NASDAQ: PCNTF