genuity - any good?

Sat Apr 13 02:44:02 UTC 2002

> 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.
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