Re: Destination Preference Attribute for BGP

[Robert Raszuk <robert () raszuk net>]

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.