BGP 4-Byte AS in aspath-prepend-count

[n3tw0rkn3rd]

Hi all,

We are trying to configure BGP 4-Byte AS with "aspath-prepend-count" parameter, but it does not seem to work.

I have read another BGP-4-Byte-AS post (BGP 4-Byte AS in routemap community), looks like CheckPoint also do not support 4-Byte-AS in AS-Prepend configuration.

Can someone please comment on this? Thank you! 

[Sundeep_Mudgal]

Check this. Will get back to you soon.

[Sundeep_Mudgal]

It works and is supported. Here is the output from R&D setup:

On my R80.30 machine, that ultimately receives the routes, “show route bgp aspath” gives:

Prefix               Nexthop              AsPath

1.0.0.0/8            10.1.1.14            (4194368),917518,917518,917518,851981,IGP.(Id-6)

2.0.0.0/8            10.1.1.14            (4194368),917518,917518,917518,851981,IGP.(Id-6)

Configuration on  machine, which sends the routes:

set as 14.14

set bgp external remote-as 1 on

set bgp external remote-as 1 export-routemap "eb" preference 1 on

set bgp external remote-as 1 peer 10.1.1.1 on

set bgp external remote-as 1 peer 10.1.1.1 aspath-prepend-count 5

set bgp external remote-as 13.13 on

set bgp external remote-as 13.13 import-routemap "ia" preference 1 on

set bgp external remote-as 13.13 peer 10.1.1.13 on

set bgp external remote-as 64.64 on

set bgp external remote-as 64.64 export-routemap "eb" preference 1 on

set bgp external remote-as 64.64 peer 10.1.1.64 on

set routemap eb id 1 on

set routemap eb id 1 allow

set routemap eb id 1 match protocol bgp

set routemap eb id 1 action aspath-prepend-count 3

set routemap ia id 1 on

set routemap ia id 1 allow

We tried both of the following ways to configure aspath-prepend-count, with peers that do and do not support 4-byte AS numbers, and the result was right in each:

set bgp external remote-as VALUE peer VALUE aspath-prepend-count VALUE

set routemap VALUE id VALUE action aspath-prepend-count VALUE

[n3tw0rkn3rd]

Thanks Sundeep!

Would you please try if this works with a long BGP 4-Byte AS number like 4200001201 (private BGP 4-Byte AS number)?

And if possible can you please also check the configuration on R80.30 and before-R80.30 machine?

Thank you!

[n3tw0rkn3rd]

Hi Sundeep,

Thanks for your reply!

Can you please also try with private BGP 4-Byte AS number (the long one) like 4200001201 to see if AS-Prepend really works?

And can you confirm if this would work with earlier version (before R80.30) machine as well?

Thank you!

[Sundeep_Mudgal · Accepted solution]

Tried a number of experiments:

• Working fine: R81.20 (AS 4111222333), sending routes to R81.20 (AS 4200001201), sending routes (with aspath-prepend-count) to R80.30 (AS 4000999000):
  1.0.0.0/8            10.1.1.14            (4000999000),4200001201,4200001201,4200001201,4111222333,IGP.(Id-6)
• Working fine: R80.30 (AS 4111222333), sending routes to R80.20 (AS 4200001201), sending routes (with aspath-prepend-count) to R80.10 (AS 4000999000):
  1/8                  10.1.1.63            (4000999000),4200001201,4200001201,4200001201,4111222333,IGP.(Id-4)
• Not working: If the last link is IBGP instead of EBGP, then the AS number isn’t prepended and the aspath-prepend-count does not apply:
  1/8                  10.1.1.64            (4200001201),4111222333,IGP.(Id-5)

Please open a task if you still cannot get it to work. It will  just be easier and faster to resolve it through the task.

[n3tw0rkn3rd]

Thanks Sundeep for your prompt help, I will contact Support Team for this!

[Chris_Atkinson · Accepted solution]

We introduced 4-byte AS support starting in R80.10 from memory.

Though versions earlier than R80.30 will be End of Support in September hence requiring an upgrade.

[n3tw0rkn3rd]

Thanks Chris!