From: Susan Hares <[email-masked]>
To: [email-masked]
Cc: [email-masked], [email-masked]
Date: Thu, 20 May 1999 08:43:26 -0400 (EDT)

Date: Tue, 18 May 1999 08:51:25 -0700
To: [email-masked]
From: Donald Gingras <[email-masked]>
Subject: Inter domain QoS
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"

18 may 99

I would like to know if anyone within this WG is working on QoS issues
associated with providing QoS between/among autonomous systems??

don gingras 
Dr. Donald F. Gingras
Code D8805
Communications and Information Systems Dept.
SPAWAR Systems Center, San Diego
53560 Hull Street
San Diego, CA 92152
Tel 619 553 0817
Fax 619 553 3058

To: Tony Li <[email-masked]>
Cc: [email-masked], [email-masked], [email-masked]
Subject: Re: AS path loop. 
Date: Mon, 03 May 1999 09:54:57 -0700
From: Enke Chen <[email-masked]>
Sender: [email-masked]

> Date:    Mon, 3 May 1999 00:33:41 -0700 (PDT)
> From:    Tony Li <[email-masked]>
> To:      [email-masked]
> CC:      [email-masked]

> 
> |  which would seem to imply not tearing down the connection, but it is
> |  still worth debate whether the information should be readvertised at all.
> 
> 
> Yes, tearing down the connection is just plain broken.

Very true. It breaks the existing deployment of the last 5+ years.

-- Enke

> 
> As to whether the information should be advertised: in general the receiver
> MUST implement the AS path check, so it's not necessary for the sender to
> filter.  It, of course, can do so...
> 
> Tony
> 

Date: Mon, 3 May 1999 00:33:41 -0700 (PDT)
From: Tony Li <[email-masked]>
To: [email-masked]
Cc: [email-masked]
Subject: Re: AS path loop.
Sender: [email-masked]

|  which would seem to imply not tearing down the connection, but it is
|  still worth debate whether the information should be readvertised at all.

Yes, tearing down the connection is just plain broken.

As to whether the information should be advertised: in general the receiver
MUST implement the AS path check, so it's not necessary for the sender to
filter.  It, of course, can do so...

Tony

Date: Mon, 3 May 1999 03:30:23 -0400 (EDT)
From: Bradley Reynolds <[email-masked]>
To: [email-masked]
Subject: AS path loop.
Sender: [email-masked]

I ran into a nasty situation with a customer over
the weekend related to this issue.  here is a simple
diagram to illustrate the topology.
 
 -------AS Y-----AS Z 
|
US (AS X)
| 
 -------AS Z

basically, our network peers with ASN Y (who has Z as a customer)
as well as ASN Z directly at another geographic location. 
We receive inconsistant annoucements from AS Z.  They basically
advertise two disjoint sets of reachability (one over each peer).

The problem ensues because we readvertise reachability information
to the set of prefixes learned with AS path (Y Z) back to Z at our
direct peer.  This causes Z to immediately tear down the connection
and complain of an AS path loop.  It basically kept bouncing bgp
every minute or so until i filtered _Z_ annoucements at our direct peer.

So, the questions are, should we be advertising Z reachability back to Z
(i.e. are there valid and rational reasons) and should Z tear down
the connection because it sees an AS loop?

the exact wording of the current internet draft (which is a bit more clear
than 1771) is:

---
The information carried by the AS_PATH attribute is checked for AS
loops. AS loop detection is done by scanning the full AS path (as
specified in the AS_PATH attribute), and checking that the autonomous
system number of the local system does not appear in the AS path. If
the autonomous system number appears in the AS path the route may be
stored in the Adj-RIB-In, but unless the router is configured to
accept routes with its own autonomous system in the AS path, the
route shall not be passed to the BGP Decision Process. Operations of
a router that is configured to accept routes with its own autonomous
system number in the AS path are outside the scope of this document.   
---

which would seem to imply not tearing down the connection, but it is
still worth debate whether the information should be readvertised at all.

thanks for your input

BR