Re: Debugging accepted routes from BGP speakers

Robert,

You are right about the echoed path being a different path.
I forgot that ebgp does next-hop-self, so the receiver of the
echo cannot be sure it is his own echo.

Easy fixed. Do next-hop-unchanged on an echo path.

Another fix would be to add a community.
However, that would be harder to implement.
Ease of implementation is important if you want your
feature implemented.

The draft mentions nothing about backup.
I do remember some years ago, Ignas asked for this kind of feedback,
so he could know whether he should install a backup on the sender end.
Suppose R1 sends a route to R2. If R2 accepts the route,
R1 would like to install a backup in its FIB. Since FIB space
is precious, R1 does not want to install a backup if R2 does not
use R1's route.

Regards,
Jakob.

From: Robert Raszuk <[email protected]>
Sent: Tuesday, November 19, 2019 1:18 AM
To: Jakob Heitz (jheitz) <[email protected]>
Cc: Job Snijders <[email protected]>; IDR <[email protected]>
Subject: Re: [Idr] Debugging accepted routes from BGP speakers

Hey Jakob,

But this is not what is being asked here.

There is need to validated if routes received on *specific* eBGP session were accepted by bgp inbound policy.

What you suggesting is also quite useful but IMO 100% orthogonal to the topic.

Reason being that in your scenario router would advertise the best path to a peer back which may not be local eBGP route. Worse I may have N eBGP session to a given peer's ASBR and I would like to make sure all of my paths has passed his policy.

Moreover as Jared said he is not so much concern of overall reachability validation. He is concerned when his most preferred path goes down does his peer has backup path(s) to him.

Kind regards,
R.

On Tue, Nov 19, 2019 at 6:19 AM Jakob Heitz (jheitz) <[email protected]<mailto:[email protected]>> wrote:
In https://tools.ietf.org/html/rfc4271#section-9.1.2
the AS loop is broken at the receiver.
Nowhere does it say that the sender must break the AS loop.
Split horizon filtering is a common practice, but nowhere
is it mandated. At least I could not find it.

If the receiver of your route were to send you back its
best path, even if it's your route, then you have your
information.

We could invent an address-family specific capability
to indicate that you wish your route to be echoed back.

Regards,
Jakob.

-----Original Message-----
From: Idr <[email protected]<mailto:[email protected]>> On Behalf Of Job Snijders
Sent: Monday, November 18, 2019 3:00 AM
To: Robert Raszuk <[email protected]<mailto:[email protected]>>
Cc: IDR <[email protected]<mailto:[email protected]>>
Subject: Re: [Idr] Debugging accepted routes from BGP speakers

On Mon, Nov 18, 2019 at 9:50 AM Robert Raszuk <[email protected]<mailto:[email protected]>> wrote:
> > The latter one is oftentimes easily validated by Internet-wide looking glasses
>
> Hmmmm I must say that IMHO both latter and former could be addressed by looking-glass. In fact when I read this draft that was my first question - why not to just look at peer's looking glass ?

Many networks unfortunately do not make BGP Looking Glasses available,
nor is there any standardized interface/method/design/approach for BGP
Looking Glasses. So solely relying on Looking Glasses for this
functionality has proven to be insufficient.

> So perhaps we should simply issue a BCP to say that each AS should run a looking glass server holding all paths and declare victory ? And that could be all GROW WG thing too :)

That is an interesting idea, but in my mind not the exclusive viable solution.

> I already see a bunch of new things we could accomplish in the Internet if we would have those in place consistently everywhere - at least for each transit AS.

Agreed - it would be a nicer world. Through the MANRS initiative I've
pitched the idea to provide more encouragement for networks to provide
looking glasses to the public, but arguably their availability is not
ubiquitous.

Another observation is that in the "IP Transit Carrier" segment of the
market we see BGP Looking Glasses from time to time, but we rarely see
similar functionality offered by Cloud/CDN providers. Perhaps the
latter category is not interested in running & maintaining looking
glasses, or perhaps there are other constraints that prevent them from
exposing this information via suchs tools. My hope is that by creating
a feedback mechanism in BGP we create more opportunity to share
debugging information specific to EBGP sessions between different
orgs.

Kind regards,

Job

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