Re: [sidr] pCNT & (AS_PATH) prepending: Is it in scope?

Jakob Heitz <jakob.heitz@ericsson.com> Mon, 01 August 2011 19:16 UTC

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From: Jakob Heitz <jakob.heitz@ericsson.com>
To: "Montgomery, Douglas" <dougm@nist.gov>, Randy Bush <randy@psg.com>, "t.petch" <ietfc@btconnect.com>
Date: Mon, 01 Aug 2011 15:16:18 -0400
Thread-Topic: [sidr] pCNT & (AS_PATH) prepending: Is it in scope?
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Subject: Re: [sidr] pCNT & (AS_PATH) prepending: Is it in scope?
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It is easy enough to tell, but should we?
It is also easy to protect other bgp attributes that affect path selection.

However, the real question is:
Do we want to invalidate an update if someone changes such an attribute?

Remember, if we send a route to an AS, even if it is less preferred
than another route, then that route will be used if the preferred route
becomes infeasible. Therefore, there is not as much value in
protecting attributes as there is in protecting the path.

I thought there was a statement some time ago that we only protect
the path, not the attributes.

A prepend is not a change in path. It is more like an attribute.

--
Jakob Heitz.
 

> -----Original Message-----
> From: sidr-bounces@ietf.org [mailto:sidr-bounces@ietf.org] On 
> Behalf Of Montgomery, Douglas
> Sent: Monday, August 01, 2011 12:02 PM
> To: Randy Bush; t.petch
> Cc: sidr@ietf.org
> Subject: Re: [sidr] pCNT & (AS_PATH) prepending: Is it in scope?
> 
> 
> 
> On 8/1/11 1:17 PM, "Randy Bush" <randy@psg.com> wrote:
> 
> >
> >
> >> Question is; how common is prepending?  I thought that it was
> >> widespread and 'normal' but there would have to be hard data first,
> >> before deprecation could be contemplated.
> >
> >we could measure.  but given that we can see that it is quite common,
> >and we have reasonable ways to deal with it, why should we spend the
> >time?  what might we learn?
> 
> 
> Randy's answer was better.  Given that it is easy to do, what 
> is the down
> side to enabling one to tell if someone else added/subtracted 
> from your
> prepend list?
> 
> Maybe to help that discussion, I will note by "tell" above, what the
> current proposal suggests is that such adding/trimming would 
> cause BGPSEC
> path validation to FAIL.
> 
> Dougm
> 
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