Subject: inclusion of AS no in AS path

From: "naresh paliwal" <[email-masked]>
Date: 25 Oct 2002 12:18:21 -0000

Is not it useful to check whether an update contains external 
peer's AS number in AS path attribute, avoiding this may introduce 
routing loop.

In other words, Are there situations/policies which could restrict 
a BGP speaker from including his AS number in the route advertised 
to an external peer ?
If yes how will routing loop be pruned?

regards
-naresh

---

From: Curtis Villamizar <[email-masked]>
Date: Tue, 29 Oct 2002 12:13:10 -0500

In message <[email-masked]>, "naresh paliwa
> If yes how will routing loop be pruned?

When advertising to an EBGP peer, a router MUST include its own AS in
the path.  I can't think of any exceptions.

Curtis

---

From: Manav Bhatia <[email-masked]>
Date: Wed, 30 Oct 2002 17:15:15 +0530

> the path.  I can't think of any exceptions.

I have seen atleast two implementations which have a flag to bypass this
wherein a router does not append its own AS number even if it is
advertising routes to its EBGP peers. One more scenario when this might
happen is when the remote peer is configured as a route server client. In
that case too, the host speaker does not append its own AS number when
advertising to an EBGP peer.

Manav

---

From: Curtis Villamizar <[email-masked]>
Date: Wed, 30 Oct 2002 11:47:42 -0500

In message <[email-masked]>, Manav Bhatia writes
> advertising to an EBGP peer.

Route servers such as those that are available at some of the NAPs act
as a filter of BGP information which should be as transparent as
possible.  These are definitely special cases.

The RS, the peer that it learned a route from, and the peer it
advertises a route to must all exist on the same broadcast network or
the RS must have other assurance that it's two EBPG peers can directly
reach each other.  The RS passes a third party route, without its own
AS to have the same effect as if the RS peers had passed the route
directly between themselves.

This is clearly a very special cases that does not have to be
reflected in the base BGP spec.  If someone (Merit?) wants to write an
internet-draft describing how a RS uses BGP, that would be fine as a
separate document describing a special usage of BGP in which some of
the base BGP rules are altered.

Curtis

---

From: Jeffrey Haas <[email-masked]>
Date: Wed, 30 Oct 2002 16:35:57 -0500

> the base BGP rules are altered.

I believe that the last of the deployed RS's at the public IX's 
will be decomissioned soon.  There are still some private IX's that
are utilizing route servers as a method of implementing controlled
policy.

Being probably one of the few advocates for use of route servers
(where appropriate), I think this definitely can slip to an external
draft.  Its also generally fine because most relevant implementations
of routers have a knob for "ignore first as" and so long as
people put this in as a "knob complete" feature, all is well.

-- 
Jeff Haas 
NextHop Technologies

---

From: Manav Bhatia <[email-masked]>
Date: Thu, 31 Oct 2002 10:12:36 +0530

Curtis,

> the base BGP rules are altered.

I am *not* at all advocating that you put this in the base spec. My reply
was in response to your statement "I can't think of any exceptions".

Manav