Subject: [Idr] Hop-limit: Hop calculation

From: "Joel M. Halpern" <[email-masked]>
Date: Tue, 14 Mar 2006 17:40:48 -0500

While reading the hop limit draft, I noticed that it says that if an 
AS Path has an AS Set (or more than one) that each element of the set 
should be counted individually.
For purposes of breaking ties across advertisements, the BGP spec 
says that one compares the length of the AS path.  The counting 
algorithm states that an AS Set is to be counted as one element for 
this purpose.

It does not seem helpful to have two different definitions for the 
length of an AS path that give different answers in some cases.

While I understand that the current choice in the hop-limit draft was 
made to reflect a meaningful case (someone along the way simply 
collapsed the elements), I believe that it can be argued that the 
existing counting is just as applicable.  And has the advantage of consistency.

Yours,
Joel M. Halpern

PS: There are some other minor reasons for suggesting this, relating 
to ways one might bend BGP.  Some of those are even why I thought of 
the question.  But I believe the above consistency is the significant issue.

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From: Paul Jakma <[email-masked]>
Date: Wed, 15 Mar 2006 02:06:03 +0000 (GMT)

> length of an AS path that give different answers in some cases.

I think the standalone decrementing TTL was nicer.

regards,
-- 
Paul Jakma	[email-masked]	[email-masked]	Key ID: 64A2FF6A
Fortune:
We are all born mad.  Some remain so.
 		-- Samuel Beckett

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From: "Tony Li" <[email-masked]>
Date: Wed, 15 Mar 2006 09:44:46 -0800

Joel,
 
> advantage of consistency.

I don't have a big problem with this.  Do other folks have opinions?

Tony

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From: Andrew Lee <[email-masked]>
Date: Wed, 15 Mar 2006 13:24:02 -0500

> I don't have a big problem with this.  Do other folks have opinions?

It seems like it would be more correct to count a set as 1 element.  For 
example, if A B and C peer with D and D announces an aggregate to E with a path 
like D {A B C}, the distance from E to any of the set is still 2.

Andrew

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From: Jeffrey Haas <[email-masked]>
Date: Wed, 22 Mar 2006 12:28:17 -0500

> I don't have a big problem with this.  Do other folks have opinions?

I think I had made a similar comment earlier.  I'm in support of this.

Other comments on the draft:

I'll note once again that the ATOMIC_AGGREGATE behavior in this document
(-01) is inconsistent with the way people actually do things.  This issue
will most certainly be raised during last-call.

I would suggest adding a sentence regarding aggregation saying that this
attribute must not be added to the aggregate, or allowing it to be
added to the aggregate iff all contributing routes have the same
path limit attribute.

:   When a BGP speaker propagates a route with an associated AS_PATHLIMIT
:   attribute, which it has learned from another BGP speaker's UPDATE
:   message, it MUST NOT modify the route's AS_PATHLIMIT attribute.

While I tend to agree with this, I doubt it'll survive implementation. :-)

-- Jeff

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From: "Tony Li" <[email-masked]>
Date: Fri, 31 Mar 2006 17:43:37 -0800

> I think I had made a similar comment earlier.  I'm in support of this.

Folks,

I've heard no further discussion on this, so unless there is some
immediate dissent, I'll be updating the draft accordingly.

Regards,
Tony