did you mean to type  ip as-path access-list 73 permit ^102(_[0-9]+*)*?$

On Sun, Nov 27, 2011 at 12:30 PM, James Roc <[email protected]> wrote:

> Hi All,
>
> This question asks to 'ensure that only directly connected clients of AS102
> can transit AS50'.
>
> AS101 - AS50 - AS102 - ASXXX
>
> The DSG uses the following inbound as-path acl on the AS50 router peering
> to AS102:
>
>   ip as-path access-list 73 permit ^102(_[0-9]+?$
>
> This filters the required routes entering AS50 from AS102 but there are no
> outbound filters.
>
> In the following topology, routes from AS101 could pass through AS50 to
> AS102 and beyond.
>
> AS101 - AS50 - AS102 - ASXXX - AS300
>
> So while AS101 would not have a synchronous return route, AS300 could still
> transit AS50 to reach AS101.
>
> Given that changes can only be done on AS50, whats the best way to prevent
> this?
>
> Cheers
> James
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