Subject: New Issue - Outbound Loop Detection

From: "Natale, Jonathan" <[email-masked]>
Date: Fri, 18 Oct 2002 13:17:22 -0400

This paper (thanks Jeff)
http://www.research.microsoft.com/scripts/pubs/view.asp?TR_ID=MSR-TR-2000-08
indicates that it
is better to do the loop detection outbound as well inbound.  The current
draft indicates that
it only needs to be done inbound.  IOS does it inbound as well as outbound.
GateD/Juniper
does it (did it ???) only inbound.

So I propose we add:
"An implementation MAY choose to not advertise routes to EBGP peers if these
routes contain
the AS of that peer in the AS path."
after:
"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 AS in the
AS path, the route shall not be passed to the BGP Decision Process."

*If there is at least one other implementation that does outbound
pruning/loop-detection.*

---

From: Yakov Rekhter <[email-masked]>
Date: Fri, 18 Oct 2002 10:31:55 -0700

Jonathan,

> indicates that it is better to do the loop detection outbound as well 
> inbound. The current draft indicates that it only needs to be done inbound. 
> IOS does it inbound as well as outbound. GateD/Juniper does it (did it ???) 
> only inbound.
> 
> So I propose we add:
> routes contain the AS of that peer in the AS path."
> after:
> stored in the Adj-RIB In, but unless the router is configured to accept 
> routes with its own AS in the AS path, the route shall not be passed to 
> the BGP Decision Process."

First of all, if we add the text you proposed it should go into 9.1.3,
and not in 9 (as Section 9 deals with processing UPDATE messages, while
Seciton 9.1.3 deals with advertising routes to peers. 

Second, we could add this sentence only if there are at least two
implementations that support it. So, folks who implement the outbound
loop detection please drop an e-mail within a week.

Yakov.