[c-nsp] BGP route filtering question about upstreams

[Mark Tinka]

On Tuesday, October 07, 2014 03:27:39 PM Andrew (Andy) 
Ashley wrote:

> What would a ³proper² routing policy with relation to
> this scenario. Providing communities, etc?

AS300 is filtering appropriately among peers.

> The idea is to avoid international paths over AS200
> ending up on the AS300 international backbone (since
> AS200 is also a transit customer of AS300).

Well, typically, customers should not announce a full table 
to their upstreams (nor should their upstreams be in a 
position to accept them).

> AS100 does not want to see any international traffic via
> AS200 that transits AS300.
> Perhaps AS300 provides cheaper international transit to
> AS200 than the other upstreams,
> so AS200 preferences international traffic over AS300,
> which is not good for AS100¹s redundancy when AS300 has
> problems. AS100 has alternate domestic routes to AS300
> via a domestic-only BGP session to AS200.

Have both AS200 and AS300 mark "local" and "international" 
routes with specific communities. Pass those communities on 
to AS100 and ask them to perform inbound filtering 
accordingly.

For the reverse, AS200 and AS300 should provide AS100 with 
communities that AS100 can use to control whether their 
routes are announced to.

Mark.
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