a crude method of limiting long-prefix propagation

[Joe Abley]

On Mon, Mar 26, 2001 at 11:15:05AM -0500, Joel M. Halpern wrote:
> If we are going to look down this path, for some cases at least, 
> DIST_LIST_EXCL (which lists where NOT to send the information) would also 
> seem useful.

The mechanism I used in the community-based approach (and which I think
Ben is using in his PROP_PATH attribute) is that if it looks like
propagation control is specified for a prefix, then not mentioning an
AS where the prefix should be announced is an implicit exclude for that
AS.

i.e. if the EPPC_ALLOW:0 community is present, and EPPC_ALLOW:A is not
present, then the prefix must not be advertised to AS A (and must not
be accepted by AS A if AS A understands the EPPC conventions, although
I added that after the -01 draft was sent out).

Correspondingly, I think the description Ben is working on will specify
that if the PROP_PATH attribute is present and AS A is not present in
the PROP_PATH, the prefix must not be advertised to or accepted by AS A.

Is there a scenario where it is better to specify "I don't want this
prefix to go to these ASes" rather than "I only want this prefix to
go to these ASes"? I like the current logic better, I think.


Joe