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REMOVE AS FROM AS_PATH ATTRIBUTE

Created: Jun 17, 2021 12:56:26Latest reply: Jun 17, 2021 14:36:16 346 3 0 0 0
  Rewarded HiCoins: 4 (problem resolved)

Hi, dears!


I'm studying to HCIP and the guide has the following question: "Whether a route-policy can be used to delete an AS from the AS_Path attribute?"


Looking for it on documentation I did't see anything about it, so is it possible? I know that removing a private AS from AS_PATH is done by "public-as-only" commands under BGP view.


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Popeye_Wang
Admin Created Jun 17, 2021 14:36:16

Hello,

In a routing policy, you can run the apply as-path command to set the action for changing the AS_Path attribute of BGP routes in a routing policy.

For example, Assume that the original AS-Path is (30, 40, 50) and the BGP route matching condition is met. In this case:

  • If the apply as-path 60 70 80 additive command is run, the AS-Path list is changed to (60, 70, 80, 30, 40, 50). This configuration change is generally used to make the BGP route not preferentially selected.

  • If the apply as-path 60 70 80 overwrite command is run, the AS-Path list is changed to (60, 70, 80). There are many application scenarios for changing the AS-Path list, and the major application scenarios are as follows:

For details, please refer to:https://support.huawei.com/hedex/hdx.do?docid=EDOC1100069307&id=apply_as-path&lang=en


View more
  • x
  • convention:

l2vc
l2vc Created Jun 17, 2021 15:07:39 (0) (0)
Hi, Wang!

But, what else if I'd like to always remove the last AS, for example? Is it possible? Like this:

before => after
AS PATH 100 200 300 => AS PATH 100 200
AS PATH 240 123 20 100 23 => AS PATH 240 123 20 100  
Popeye_Wang
Popeye_Wang Reply l2vc  Created Jun 18, 2021 07:27:37 (1) (0)
There is no way to create a route policy to delete the last AS in a unified manner. You can only create multiple route policies and apply them to different BGP peers to delete related AS.
For AS PATH 100 200 300, apply as-path 100 200 overwrite
For AS PATH 240 123 20 100 23, apply as-path 240 123 20 100 overwrite  
All Answers

Hello,

In a routing policy, you can run the apply as-path command to set the action for changing the AS_Path attribute of BGP routes in a routing policy.

For example, Assume that the original AS-Path is (30, 40, 50) and the BGP route matching condition is met. In this case:

  • If the apply as-path 60 70 80 additive command is run, the AS-Path list is changed to (60, 70, 80, 30, 40, 50). This configuration change is generally used to make the BGP route not preferentially selected.

  • If the apply as-path 60 70 80 overwrite command is run, the AS-Path list is changed to (60, 70, 80). There are many application scenarios for changing the AS-Path list, and the major application scenarios are as follows:

For details, please refer to:https://support.huawei.com/hedex/hdx.do?docid=EDOC1100069307&id=apply_as-path&lang=en


View more
  • x
  • convention:

l2vc
l2vc Created Jun 17, 2021 15:07:39 (0) (0)
Hi, Wang!

But, what else if I'd like to always remove the last AS, for example? Is it possible? Like this:

before => after
AS PATH 100 200 300 => AS PATH 100 200
AS PATH 240 123 20 100 23 => AS PATH 240 123 20 100  
Popeye_Wang
Popeye_Wang Reply l2vc  Created Jun 18, 2021 07:27:37 (1) (0)
There is no way to create a route policy to delete the last AS in a unified manner. You can only create multiple route policies and apply them to different BGP peers to delete related AS.
For AS PATH 100 200 300, apply as-path 100 200 overwrite
For AS PATH 240 123 20 100 23, apply as-path 240 123 20 100 overwrite  

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