Hello James,
On 15/7/25 5:00 AM, James Bensley wrote:
Hi all,
I'm reading v16 of this document.
Section 5 - Best Practices.
"""
Use of local-preference inbound on preferred paths between service
providers to help mitigate the adverse effects of prepending
"""
The statement right before this makes it clear that AS path prepending
might not work if the neighbouring network is using i.e. Local Pref:
"""
The neighbor, to which prepending is used, may have an unconditional
preference for customer routes and prepending doesn't work. It is
helpful to check with neighbors to see if they will honor the prepend
to avoid wasting effort and potentially causing further vulnerabilities.
"""
This is exactly why Local Pref shouldn't be used for TE (in my
opinion). There are a bunch of problems with Local Pref and it should
be avoided.
Can you elaborate this is a little bit more?. Why do you think Local
Pref should be avoided?
I think that any best practice recommendations should come with
justifications for why they make good practice. If Local Pref is going
to be provided as a best practice recommendation, there needs to be a
justification here. Otherwise this is a statement which hasn't been
justified.
Cheers,
James.
On Monday, July 7th, 2025 at 21:42, [email protected]
<[email protected]> wrote:
> Internet-Draft draft-ietf-grow-as-path-prepending-16.txt is now
available. It
> is a work item of the Global Routing Operations (GROW) WG of the IETF.
> Title: AS Path Prepending
> Authors: Mike McBride
> Doug Madory
> Jeff Tantsura
> Robert Raszuk
> Hongwei Li
> Jakob Heitz
> Gyan Mishra
> Name: draft-ietf-grow-as-path-prepending-16.txt
> Pages: 13
> Dates: 2025-07-07
> Abstract:
> Autonomous System (AS) path prepending is a tool to manipulate the
> BGP AS_PATH attribute through prepending one or more Autonomous
> System Numbers (ASNs). AS path prepending is used to deprioritize a
> route in the presence of a route with a shorter AS_PATH. By
> prepending a local ASN multiple times, ASes can make advertised AS
> paths appear artificially longer. However, excessive AS path
> prepending has caused routing issues in the Internet. This document
> provides guidance for the use of AS path prepending, including
> alternative solutions, in order to avoid negatively affecting the
> Internet.
> The IETF datatracker status page for this Internet-Draft is:
> https://datatracker.ietf.org/doc/draft-ietf-grow-as-path-prepending/
> There is also an HTMLized version available at:
>
https://datatracker.ietf.org/doc/html/draft-ietf-grow-as-path-prepending-16
> A diff from the previous version is available at:
>
https://author-tools.ietf.org/iddiff?url2=draft-ietf-grow-as-path-prepending-16
> Internet-Drafts are also available by rsync at:
> rsync.ietf.org::internet-drafts
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