[88041] in North American Network Operators' Group
Re: PI space and colocation
daemon@ATHENA.MIT.EDU (Stephen Sprunk)
Wed Jan 18 17:51:31 2006
From: "Stephen Sprunk" <stephen@sprunk.org>
To: "Chris Adams" <cmadams@hiwaay.net>
Cc: "North American Noise and Off-topic Gripes" <nanog@merit.edu>
Date: Wed, 18 Jan 2006 16:49:18 -0600
Errors-To: owner-nanog@merit.edu
Thus spake "Chris Adams" <cmadams@hiwaay.net>
> Once upon a time, Patrick W. Gilmore <patrick@ianai.net> said:
>> It adds zero useful data to the global table, but increases RAM, CPU,
>> etc. on every router looking at the global table.
>
> How much difference is there between one AS (the colo provider)
> announcing a prefix and another AS (the customer) announcing it through
> the first AS (the colo provider)? If the space is ARIN assigned PI, it
> isn't going to aggregate with the colo provider's space, so the prefix
> will still be a separate announcement. The only difference is the AS
> path is one entry longer.
Routing slots aren't the only resource you're consuming. In general, many
of the prefixes coming out of a given AS have common attributes, e.g. path,
MEDs, etc. Those attributes are stored only once (at least in the BGP
implementation I know) even if they're used by hundreds of prefixes. If you
attach a new leaf AS, it must, by necessity, consume another one of those
slots. If the customer prefix were announced by the upstream, however, it
would not require an additional attribute slot; it'd reuse one of the
existing ones.
Now, I'm not aware that there's any serious shortage of attribute slots like
there is routing slots, but there's no sense wasting them if there's no gain
to be had doing it. Save your (and everyone else's) RAM for more prefixes.
S
Stephen Sprunk "Stupid people surround themselves with smart
CCIE #3723 people. Smart people surround themselves with
K5SSS smart people who disagree with them." --Aaron Sorkin
