[c-nsp] BGP route filtering question about upstreams

[Mark Tinka]

On Tuesday, October 07, 2014 01:47:42 PM Andrew (Andy) 
Ashley wrote:

> AS100 does not want AS300 to learn its routes from AS200,
> since that can cause redundancy issues (2 supposedly
> diverse upstreams effectively become 1).

Well, if AS100 is announcing consistently to both AS200 and 
AS300, and AS300 has a proper routing policy, this should 
not be an issue.

Issues arise if AS100 is routing inconsistently, and/or if 
AS300 has a dodgy routing policy.

> AS100 still wants to receive a full table from AS200 (but
> not routes that transit AS300).

Routes that transit AS300 to/from where? AS100? AS300? The 
rest of the Internet?

> AS100 asks AS200 to filter its announcements to AS300.

This is outbound routing toward AS300.

> AS100 now still receives routes that are learned from
> AS300 via AS200.

This is inbound routing toward AS100.

> It should be possible for AS200 to tag prefixes learned
> from AS300 at ingress, then implement a policy to filter
> these tagged prefixes on outbound announcements to
> AS100.
> But, how can AS100 still receive a full table from AS200
> with such filtering in place?

That's why I asked above - what routes does AS100 not want 
to see that transit AS300? AS100's own routes (own-AS-in 
would fix that anyway), AS300's own routes, or the rest of 
the Internet?

Mark.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 836 bytes
Desc: This is a digitally signed message part.
URL: <https://puck.nether.net/pipermail/cisco-nsp/attachments/20141007/7bdaddcc/attachment.sig>