Re: Destination Preference Attribute for BGP

["Jakob Heitz \(jheitz\) via NANOG" <nanog () nanog org>]

That's true Robert.
However, communities and med only work with neighbors.
Communities routinely get scrubbed because they cause increased memory usage and convergence time in routers.
Even new path attributes get scrubbed, because there have been bugs related to new ones in the past.
Here is a config snippet in XR

router bgp 23456
attribute-filter group testAF
  attribute unrecognized discard
!
neighbor-group testNG
  update in filtering
   attribute-filter group testAF

The only thing that has any chance to go multiple ASes is as-path.
Need to be careful with that too because long ones get dropped.

route-policy testRP
  if as-path length ge 200 then
    drop
  endif
end-policy

Kind Regards,
Jakob


From: Robert Raszuk <robert () raszuk net>
Date: Friday, August 18, 2023 at 12:38 AM
To: Jakob Heitz (jheitz) <jheitz () cisco com>
Cc: nanog () nanog org <nanog () nanog org>
Subject: Re: Destination Preference Attribute for BGP
Jakob,

With AS-PATH prepend you have no control on the choice of which ASN should do what action on your advertisements.

However, the practice of publishing communities by (some) ASNs along with their remote actions could be treated as an 
alternative to the DPA attribute. It could result in remote PREPEND action too.

If only those communities would not be deleted by some transit networks ....

Thx,
R.

On Thu, Aug 17, 2023 at 9:46 PM Jakob Heitz (jheitz) via NANOG <nanog () nanog org<mailto:nanog () nanog org>> wrote:
"prepend as-path" has taken its place.

Kind Regards,
Jakob


Date: Wed, 16 Aug 2023 21:42:22 +0200
From: Mark Tinka <mark@tinka.africa>

On 8/16/23 16:16, michael brooks - ESC wrote:

> Perhaps (probably) naively, it seems to me that DPA would have been a
> useful BGP attribute. Can anyone shed light on why this RFC never
> moved beyond draft status? I cannot find much information on this
> other than IETF's data tracker
> (https://datatracker.ietf.org/doc/draft-ietf-idr-bgp-dpa/) and RFC6938
> (which implies DPA was in use,?but then was deprecated).

I've never heard of this draft until now, but reading it, I can see why
it would likely not be adopted today (not sure what the consensus would
have been back in the '90's).

DPA looks like MED on drugs.

Not sure operators want remote downstream ISP's arbitrarily choosing
which of their peering interconnects (and backbone links) carry traffic
from source to them. BGP is a poor communicator of bandwidth and
shilling cost, in general. Those kinds of decisions tend to be locally
made, and permitting outside influence could be a rather hard sell.

It reminds me of how router vendors implemented GMPLS in the hopes that
optical operators would allow their customers to build and control
circuits in the optical domain in some fantastic fashion.

Or how router vendors built Sync-E and PTP into their routers hoping
that they could sell timing as a service to mobile network operators as
part of a RAN backhaul service.

Some things just tend to be sacred.

Mark.