Destination Preference Attribute for BGP

Wed Aug 30 16:56:48 UTC 2023

>With AS-PATH prepend you have no control on the choice of which ASN should
do what action on your advertisements.
Robert- It is somewhat this problem we are trying to resolve.

>I was imagining something sexier, especially given how pretty "useless"
AS_PATH prepending is nowadays.
I, too, am looking for something sexy (explained below). But can you
explain why you think AS_PATH is "useless," Mark?

For background, and the reason I asked about DPA:
Currently, our routing carries user traffic to a single data center where
it egresses to the Internet via three ISP circuits, two carriers. We are
peering on a single switch stack, so we let L2 "load balance" user flows
for us. We have now brought up another ISP circuit in a second data center,
and are attempting to influence traffic to return the same path as it
egressed our network. Simply, we now have two datacenters which user
traffic can egress, and if one is used we want that traffic to return to
the same data center. It is a problem of asymmetry. It appears the only
tools we have are AS_Path and MED, and so I have been searching for another
solution, that is when I came across DPA. In further looking at the
problem, BGP Communities also seems to be a possible solution, but as the
thread has explored, communities may/may not be scrubbed upstream. So,
presently we are looking for a solution which can be used with our direct
peers. Obviously, if someone has a better solution, I am all ears.

A bit more info: we are also looking at an internal solution which passes
IGP metric into MED to influence pathing.

To avoid TL;DR I will stop there in the hopes this is an intriguing enough
problem to generate discussion.

michael brooks
Sr. Network Engineer
Adams 12 Five Star Schools
michael.brooks at adams12.org
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
"flying is learning how to throw yourself at the ground and miss"

On Fri, Aug 18, 2023 at 1:39 AM Robert Raszuk <robert at raszuk.net> wrote:

> 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 at 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 at 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/
>> <https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-ietf-idr-bgp-dpa/__;!!IR39LLzvxw!LfO7m5JiQpZx6Lp-F2LQMBHi-YefsPMl8GdYkbrFSGWXd0G3HHj6wxEJv7_K0Y-_pIAyvahmJPXvcHAc251UDA$>)
>> 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.
>>
>>

-- 
This is a staff email account managed by Adams 12 Five Star Schools.  This 
email and any files transmitted with it are confidential and intended 
solely for the use of the individual or entity to whom they are addressed. 
If you have received this email in error please notify the sender.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.nanog.org/pipermail/nanog/attachments/20230830/aa5ee12a/attachment.html>