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I have a situation as below:

Consider my local AS value is 65002 and the neighbor AS has value 333. If my AS path shows the value as AS_PATH:65002 333, then on using set-prepend-local-as as 2, what is the expected behavior in AS_PATH value?

Should it be AS_PATH: 65002 65002 333 or AS_PATH: 65002 65002 65002 333 ?

In other words, if set-prepend-local-as is set, then the value of local AS must prepend the number of times specified(result = number of times*AS + existing AS)?

Note: The local AS number is present already in AS path before prepending(I think by default while exporting it adds local AS once). Please specify if there is any document that specifies the expected behavior.

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  • Please let me know if you still have any concerns regarding my answer to your question?
    – Hung Tran
    Commented Sep 25, 2017 at 13:31
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin ♦
    Commented Feb 19, 2018 at 19:36

1 Answer 1

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I believe you are not using Cisco/Juniper devices. They do NOT support the command set-prepend-local-as but Datacom does.

To asnwer your question, as you have AS_PATH:65002 333, with the command set-prepend-local-as 2 you will get AS_PATH:65002 65002 333, that means the result = number_of_times*Local_AS.

You can check the sample configuration on Datacom device at here

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  • When you advertise the route to eBGP neighbor, your local AS (65002) will be prepended into AS-Path (only one value by default) as "65002 333 i". With your router/device type (Datacom), when you use the command set-prepend-local-as 2, the default behavior is modified and the device prepend 2 values of 65002 as "65002 65002 333 i", with set-prepend-local-as 3, it would be "65002 65002 65002 333 i", I hope it is clearer now.
    – Hung Tran
    Commented Oct 9, 2017 at 9:01

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