Subject: Usage of IPv6 flow label

From: Metzler Jochen <[email-masked]>
Date: Wed, 15 Nov 2000 12:55:42 +0100

Hi all,
I have some questions depending the usage of the flow
label field within IPv6. Background of my questioning is
that actually within 3GPP standardization the discussion 
appears if the flow label could be used for bearer 
identification if IPv6 would be chosen as transport
option within the UMTS Radio Access Networks.

Within RFC2460 the usage of the flow label field is not
fully described and for me it is not clear if anything
mentioned in the Appendix is part of the standard or 
only for information. Therefore I have the following 
questions:

- Would the flow label be set by the Application?
  As far as I could see from the API description
  the flow label would be set from the application layer,
  can also be read by the application layer and must be chosen 
  pseudo-randomly. Are there any further restrictions?

- Can intermediate routers change the flow label?
  Appendix A of RFC2460 states that hosts or routers that
  do not support the flow label should pass the field on 
  unchanged. Is this also true for hosts or routers that
  do support the flow label? What is the procedure if an
  router supports flow labels but has no context about a
  specific flow label? 

- Are there any ideas how to use the flow label field in 
  the future, especially with respect to non-default QoS? 

- In our view IP flows are quit similar to what is called
  transport bearer within an UMTS RAN. Are there any 
  objections that preclude mapping of transport bearers
  to IP flows?

and last but not least:
- Is this the right place to put my questions or are there
  other WGs involved into flow label processing?

Cheers Jochen
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From: Jun-ichiro itojun Hagino <[email-masked]>
Date: Wed, 15 Nov 2000 21:27:46 +0900

>only for information. Therefore I have the following 

	I tried to clarify some of the issues with flowlabel and its API,
	it is documented in draft-itojun-ipv6-flowlabel-api-00.txt.  i really
	appreciate your feedbacks.  i'll be presenting about it at San Diego
	IETF.

>  router supports flow labels but has no context about a

	seems to me, no.

itojun

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From: Thomas Narten <[email-masked]>
Date: Wed, 15 Nov 2000 09:44:08 -0500

Metzler,

> only for information. Therefore I have the following 

The bottom line is that as of this time, no one has proposed how they
would like to use the Flow Label and led the WG to consensus on their
approach. Hence, it really is unspecified in the sense that its
useage/definition remains to be defined.

If you have a proposal on how it could/should be used, this WG is
certainly the place to make that proposal, and I would encourage you
to do so.

I'll note that there have been discussions in the past where arguments
have been made that the flow label should not be modified by any
routers (i.e., it has end-to-end semantics that need to respected)
while other folks have argued that it might be good to allow it to be
modified by routers (e.g., in support of something like MPLS). The
door has been left open for either of those approaches. Specifically,
the Flow Label is considered a mutable field from the perspective of
IPsec, thus IPsec won't break if the field is modified by routers.

Again, what is needed is a concrete proposal that answers the types of
questions you raised.

Thomas

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From: Jim Bound <[email-masked]>
Date: Thu, 16 Nov 2000 05:07:08 -0500

Jochen,

The flow label is used in RSVP with IPv6 and we have implemented it.
I believe it could be used as b-service for 3GPP but you need to make
proposal to this list.

If you need implementation input let me know offline.

ALso there are other than 3GPP users that want to do the same thing that
will need to identify b-services.  I can discuss with you offline.

regards,
/jim

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From: Alex Conta <[email-masked]>
Date: Thu, 16 Nov 2000 14:23:15 -0500

Thomas,

This is or may be a sensitive topic for many. 

The reality is that, at least a majority, if not all, of the original
goals of the Flow ID field
are achieved by the MPLS shim header. Remember the discussions of many
years ago, of where to place the flow ID relative to the source and
destination addresses? Well that was also answered by the MPLS header.

Furthermore, The MPLS label distribution protocols - RSVP is one of 
them - are the mechanisms used to assign and distribute labels. IPng WG
never really tackled this area, and in reality there is no protocol that
defines a consistent IPv6 flow ID allocation, and distribution
that I am aware of.
  
Furthermore, the ability to build hierarchies, the ability to use
directly fast ATM, and FR 
hardware forwarding engines, and the better traffic engineering
capabilities, give a considerable 
edge to MPLS, over the IPv6 flow ID. 

Considering these, and perhaps more, I think the IPv6 flow ID field is
obsolete, and could be 
redefined as "reserved", or renamed, and given a more useful role than
it has now. 
 
I may put out a draft on this topic, to generate or add to a discussion
point on the agenda, if one already exists.

Alex

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From: Jim Bound <[email-masked]>
Date: Mon, 20 Nov 2000 23:33:41 -0500

Alex,

RSVP uses the flow label in IPv6.

/jim

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From: Alex Conta <[email-masked]>
Date: Tue, 21 Nov 2000 15:41:04 -0500

Jim,

As there were a good number of messages on this topic, I am not sure
what particular message is your message in reference to, and what you
meant to say.
My guess could be wrong, nevertheless, if you meant to say that some
RSVP messages may carry the IPv6 flow label, I could add that some and
perhaps same RSVP messages may carry MPLS labels.
  
Alex

---

From: Jim Bound <[email-masked]>
Date: Tue, 21 Nov 2000 19:39:39 -0500

Hi Alex,

>perhaps same RSVP messages may carry MPLS labels.
  
Agreed on MPLS for RSVP.

I was responding to the general notion that we no longer need e2e from
client to client immutable flowlabel.  I strongly disagree and in fact
market expectation is now in fact we will have that with IPv6 especially
around 3GPP deployment.

Now if we can figure out away to set a bit to say in this case the
flowlabel is mutable, though I find this disgusting, I can see how I for
one would compromise and go along with it.  See my response to Thomas
Eklund I just sent.

regards,
/jim