Subject: Review Comments: Section 4.3: "route" vs. destination - withdraw

From: "Michael C. Cambria" <[email-masked]>
Date: Sat, 07 Sep 2002 13:35:26 -0400

From a first time reader point of view ...

When I read these two paragraphs at the end of section 4.3:

"An UPDATE message can list multiple routes to be withdrawn from 
service.  Each such route is identified by its destination (expressed as 
an IP prefix), which unambiguously identifies the route in the context 
of the BGP speaker - BGP speaker connection to which it has been 
previously advertised.

An UPDATE message might advertise only routes to be withdrawn from 
service, in which case it will not include path attributes or Network 
Layer Reachability Information. Conversely, it may advertise only a 
feasible route, in which case the WITHDRAWN ROUTES field need not be 
present."

It reads as if one must withdraw the _set of destinations_ advertised 
with the route instead of just one or more destinations since route is 
defined in section 3.1 as:

"For the purpose of this protocol, a route is defined as a unit of 
information that pairs a set of destinations with the attributes of a 
path to those destinations.  The set of destinations are the systems 
whose IP addresses are reported in the Network Layer Reachability 
Information (NLRI) field and the path is the information reported in the 
path attributes field of the same UPDATE message."

Shouldn't the text change "routes" to destinations, or to prefixes?

MikeC

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From: "Michael C. Cambria" <[email-masked]>
Date: Sat, 07 Sep 2002 21:35:49 -0400

> defined in section 3.1 as:

I meant to say, the *same* set of destinations as those advertised 
initially.  For example, NLRI with dest-a, dest-b and dest-c with the 
same attributes is a "route".  The withdrawal of the "route" can be read 
as one must withdraw all destinations originally advertised for that 
route (dest-a, dest-b, dest-c) as a unit.

A first time reader could be left wondering if the above must be the 
case, or it is valid for an implementation to withdraw just one of these 
destinations (e.g. dest-b), leaving the others (dest-a, dest-c) 
reachable with their attributes intact.

If there is no relationship between destinations when advertised as a 
set of destinations in a route and those destinations that can be 
withdrawn should be explicitly stated.  Otherwise, the draft should call 
out that it is not legal to withdraw one prefix only in the set of 
prefixes advertised as previously as route.

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From: Mathew Richardson <[email-masked]>
Date: Mon, 9 Sep 2002 11:24:10 -0400

> Michael C. Cambria <[email-masked]> [Sat, Sep 07, 2002 at 01:35:26PM -0400]:
>

<snip>

Since this definition seems to result in a lot of confusion, how about
changing the definition of route as follows:

  "For the purpose of this protocol, a route is defined as a unit of
  information that pairs a set of destinations with the attributes of a
  path to those destinations.  The set of destinations are systems whose
  IP addresses are reported in one prefix present in the Network Layer
  Reachability Information (NLRI) field of an UPDATE and the path is the
  information reported in the path attributes field of the same UPDATE
  message.

  This definition allows multiple routes to be advertised in a single
  UPDATE message by including multiple prefixes in the NLRI field of
  the UPDATE.  All such prefixes must be associated with the same set
  of path attributes."

mrr

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From: Yakov Rekhter <[email-masked]>
Date: Fri, 20 Sep 2002 09:54:09 -0700

Matt,

>   the UPDATE.  All such prefixes must be associated with the same set

How about some minor rewording of your text, as follows:

   For the purpose of this protocol, a route is defined as a unit
   of information that pairs a set of destinations with the attributes
   of a path to those destinations. The set of destinations are
   systems whose IP addresses are contained in one IP address prefix
   carried in the Network Layer Reachability Information (NLRI)
   field of an UPDATE message and the path is the information
   reported in the path attributes field of the same UPDATE message.

   Multiple routes that have the same path attributes can be
   advertised in a single UPDATE message by including multiple
   prefixes in the NLRI field of the UPDATE message.

Yakov.

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From: Jeffrey Haas <[email-masked]>
Date: Fri, 20 Sep 2002 13:46:52 -0400

Being one of the biggest complainers about the current text:

>    prefixes in the NLRI field of the UPDATE message.

I love this. :-)

-- 
Jeff Haas 
NextHop Technologies

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From: Mathew Richardson <[email-masked]>
Date: Fri, 20 Sep 2002 14:36:22 -0400

> Yakov Rekhter <[email-masked]> [Fri, Sep 20, 2002 at 09:54:09AM -0700]:

<snip>

<snip>

Sounds good :).

mrr