Subject: RE: draft-rajahalme-ipv6-flow-label-00.txt

From: Craig Dunk <[email-masked]>
Date: Thu, 20 Dec 2001 12:02:57 -0500

I like the rule below as it seems to nicely separate responsibilities.

Will it be self evident when (others) are applying the specific mechanisms
mentioned that the flow label (being unprotected) should not be used in a
way that circumvents normal routing rules or security policies? 

Craig.

-----Original Message-----
From: Margaret Wasserman [mailto:[email-masked]]
Sent: December 20, 2001 11:50 AM
To: [email-masked]
Subject: Re: draft-rajahalme-ipv6-flow-label-00.txt

Hi All,

I am wondering why we should specify the use of the flow label as
part of the base IPv6 specifications at all.  Why do we need
these rules as part of IPv6?  

The flow label does not, by itself, provide any useful information
that a router can use to classify a flow and/or optimize packet
handling.  In fact, without knowledge of a specific signalling
mechanism or flow-establishment mechanism, the router can't
use the flow label for anything at all.  For example, a router 
cannot use a flow label for QoS queuing or to optimize hop-by-hop 
header processing, unless the router is aware of the signalling/
flow-establishment mechanism in use, since it will not 
know the flow lifetime.

Any rules governing how the flow label is chosen, modified,
authenticated and/or interpreted will be specific to the 
signalling/flow-establishment mechanism in use.  And, all of 
the nodes/routers that are utilizing one of these mechanisms
will be aware of the mechanism.

So why not specify the semantics/use/etc. of the flow label as
part of the signalling/flow establishment protocols?

The IPv6 specifications could merely include the current rule:

"Hosts or routers that do not support the functions of the Flow Label 
field are required to set the field to zero when originating a packet, 
pass the field on unchanged when forwarding a packet, and ignore the 
field when receiving a packet." [from RFC 2460].

This rule should properly protect the flow label, so that
signalling/flow-establishment mechanisms can use the flow
label, as needed by the specific mechanism.

Margaret

--------------------------------------------------------------------
IETF IPng Working Group Mailing List
IPng Home Page:                      http://playground.sun.com/ipng
FTP archive:                      ftp://playground.sun.com/pub/ipng
Direct all administrative requests to [email-masked]
--------------------------------------------------------------------
--------------------------------------------------------------------
IETF IPng Working Group Mailing List
IPng Home Page:                      http://playground.sun.com/ipng
FTP archive:                      ftp://playground.sun.com/pub/ipng
Direct all administrative requests to [email-masked]
--------------------------------------------------------------------

---

From: Brian E Carpenter <[email-masked]>
Date: Thu, 20 Dec 2001 18:35:40 +0100

No, I think the immutability property must be specified in general.
You can't tell by looking at an opaque 20 bit number whether it's
being used for one purpose or another, so without immutability
being required, it is a useless field (at least for intserv or
diffserv).

I agree that in the end we need very few words. The sentence you
quote, plus

  In all cases, the flow label in the packet delivered to the
  destination node must be identical to the flow label in the
  packet sent by the source node.

would do it for me. All the rest of the text is rationale.

  Brian