Hi Jakob,

On Fri, Aug 18, 2023 at 7:41 PM Jakob Heitz (jheitz) via NANOG <nanog@nanog.org> wrote:

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.


Considering that we are talking about control plane memory I think the cost/space associated with storing communities is less then negligible these days. 

And honestly with the number of BGP update generation optimizations I would not say that they contribute to longer protocol convergences in any measurable way. 

To me this is more of the no trust and policy reasons why communities get dropped on the EBGP peerings. 

Cheers,
R.





 

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> 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.