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New Member

regular expression _154$ and concept

Requirement :

Part of the acquisition agreement between AS 300 and AS 200 includes stipulations on what traffic AS 300 will provide transit for.

This agreement states that AS 300 will not provide transit for traffic coming from AS 60 and its customers, that is destined for AS 154. Configure AS 300 to reflect this policy

Configuration:

router bgp 300

neighbor 204.12.1.154 route-map STOP_TRANSIT_TO_AS_154 out

!

ip as-path access-list 5 permit _154$

!

route-map STOP_TRANSIT_TO_AS_154 deny 20

match as-path 5

!

route-map STOP_TRANSIT_TO_AS_154 permit 30

My query is:

We know AS_PATH is the sequence of AS numbers (values)that a route has traversed to reach a destination(my case AS 154).

The AS that originates (my case AS 60) the route adds its own AS number when sending the route to its external peers. Thereafter, each AS that receives the route and passes it on to another BGP will prepend (Prepending is the act of adding the As number to the beginning of the list) its own AS number to the list.

So,the _154$ means anything originating FROM AS 154, but having passed through ANOTHER AS.

Now the question says :

"AS 300 will not provide transit for traffic coming from AS 60 (originating) and its customers, that is destined for AS 154 (destination)".

Is the above right configuration

4 REPLIES
VIP Purple

Re: regular expression _154$ and concept

Hello,

the configuration is perfectly all right. What you actually do is that you stop advertising prefixes from AS 154 to AS 60, hence making it impossible for AS 60 to get to AS 154.

Regards,

GP

New Member

Re: regular expression _154$ and concept

"What you actually do is that you stop advertising prefixes from AS 154 to AS 60, hence making it impossible for AS 60 to get to AS 154."

But my understanding to the question is :

I have to stop advertising prefixes form AS 60 to AS 154, not vice versa,,,Am I right ?

New Member

Re: regular expression _154$ and concept

Any idea

New Member

Re: regular expression _154$ and concept

Any idea or thought ?

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