How many legitimate cases when Origin AS in BGP announcement changed by another AS?

[akmal_shahbaz at yahoo.com (Akmal Shahbaz)]

>>When the old origin AS was a private one? 
NO.Even when old origin AS is not private one.

Don't you think private/pubic AS won't matter in case of provider aggregation?

Thanks

Akmal

--- On Tue, 1/4/11, Stephane Bortzmeyer <bortzmeyer at nic.fr> wrote:

From: Stephane Bortzmeyer <bortzmeyer at nic.fr>
Subject: Re: How many legitimate cases when Origin AS in BGP announcement changed  by another AS?
To: "Akmal Shahbaz" <akmal_shahbaz at yahoo.com>
Cc: nanog at nanog.org
Date: Tuesday, January 4, 2011, 4:05 PM

On Tue, Jan 04, 2011 at 04:38:19AM -0800,
 Akmal Shahbaz <akmal_shahbaz at yahoo.com> wrote 
 a message of 443 lines which said:

> I am looking for example routing policies when any AS receiving BGP
> advertisement changes Origin AS in BGP AS set attribute to remove
> the received AS number and puts its own AS number.[legitimate cases]

When the old origin AS was a private one? Today, with 32bits AS,
everyone should have a public AS number but, in the real world, some
people do BGP with private AS that the upstream provider has to
change.