nanog mailing list archives

Re: AS PATH limits

From: Tim Evens <tim () snas io>
Date: Wed, 20 Sep 2017 10:34:39 -0700



An AS_PATH is encoded with one or more segments. Each segment has a
maximum size of 255 entries (8 bit segment length). The absolute limit
will depend on the complete BGP message size, which is limited to 4096
and extended via draft-ietf-idr-bgp-extended-messages. 

The longest as_path at this time (changes frequently though) is 51
entries, but in the past we have seen as many as 501. 

Below is an example showing an excessive amount of prepending for prefix
185.135.134.0/23 at 2017-09-18 20:20:05 UTC. 

as_path_count: 501
as_path: 38726 9957 17604 7922 6830 197451 197451 197451 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
207239 207239 207239 207239 207239 207239 207239 207239 207239 207239
201228 

--Tim 

On 19.09.2017 06:33, craig washington wrote:

Hello world.

I was wondering and forgive me if this discussions has already taken place.

How many AS PATHS are too many?

Meaning how do we determine how many to filter on transit links or public peering links?

Thanks in advance

Current thread:

AS PATH limits craig washington (Sep 20)
- Re: AS PATH limits valdis . kletnieks (Sep 20)
- Re: AS PATH limits Tim Evens (Sep 20)
  - Re: AS PATH limits Randy Bush (Sep 20)
    - Re: AS PATH limits jim deleskie (Sep 20)
- Re: AS PATH limits Tom Beecher (Sep 20)
  - Re: AS PATH limits craig washington (Sep 22)
- <Possible follow-ups>
- RE: AS PATH limits Jakob Heitz (jheitz) (Sep 21)
- Re: AS PATH limits Ken Chase (Sep 30)
  - Re: AS PATH limits sthaug (Sep 30)
    - Re: AS PATH limits jim deleskie (Sep 30)
    - Message not available
    - Re: AS PATH limits Ken Chase (Sep 30)
    - Re: AS PATH limits Christopher Morrow (Sep 30)

(Thread continues...)