How to change BGP AS PATH

[Chetan Kumar Ress]

Hi Guys,

I would like to make clear myself ... I was looking into some modification in AS PATH ..

I have a question that can we change the AS path of a route that received from other AS... Below is the example:

AS 65000   ===== AS 66000 ==== AS67000 ==== AS68000

      ||=====================================||

1] AS 65000 is directly connected to AS 68000 & AS 66000

2] AS 65000 prep end AS for only neighbor AS 68000 not for AS 66000

Then shortest AS path will work here ...for best route selection in AS68000

AS65000 prep end AS with 65001 65002 65003 for neighbor AS68000 not for any other.

When we see any route in AS 68000... He will prefer route from AS67000 not from 65000 due to as path.

I would like to know is there any way to change AS PATH in AS68000 in inbound direction for neighbor 65000 so that I can make it shorten, so that it will prefer all route from AS6500 which is really shortest path

I don't want to use MED in AS6800 to do that.

Regards

Chetan Kumar

[Peter Paluch]

Hello,

To my best knowledge, there is no way to arbitrarily shorten the AS_PATH attribute in a way similar to AS_PATH prepending. Having an ability to remove elements from the AS_PATH would introduce a possibility of routing loops, defeating one of the major purposes of the AS_PATH attribute.

The proper (and the easiest) way of doing this would be using the LOCAL_PREFERENCE attribute in the AS 68000. Note that the MED is a different attribute. Do you have any reasons why the LOCAL_PREFERENCE would not be an appropriate solution?

Best regards,

Peter