Re: [Roll] WGLC for draft-thubert-6man-flow-label-for-rpl-03

Michael Richardson <mcr+ietf@sandelman.ca> Mon, 04 August 2014 14:15 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Ole Troan <otroan@employees.org>
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Date: Mon, 04 Aug 2014 10:15:15 -0400
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Cc: roll <roll@ietf.org>, 6man WG <ipv6@ietf.org>, Brian E Carpenter <brian.e.carpenter@gmail.com>
Subject: Re: [Roll] WGLC for draft-thubert-6man-flow-label-for-rpl-03
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On 01 Aug 2014, at 21:58 , Brian E Carpenter <brian.e.carpenter@gmail.com> wrote:
    >> It is true that the RFC also says
    >>
    >> A forwarding node MUST either leave a non-zero flow label value
    >> unchanged or change it only for compelling operational security
    >> reasons...
    >>
    >> There is a case for arguing that flow-label-for-rpl should carry the
    >> legend "Updates: 6437 (if approved)" because it adds another exception
    >> to this sentence. There is also a case for arguing that
    >> flow-label-for-rpl is a stateful mechanism, out of scope for RFC 6437
    >> according to Section 4 of that RFC.
    >>
    >> Either way, I don't see a problem.

Ole Troan <otroan@employees.org> wrote:
    > I see the principles in these two documents as mutually exclusive:
    > RFC6437: middleboxes can mess with the flow label -flow-label-for-rpl:
    > networks uses flow label field as an immutable protocol field

    > you can't both use the flow label as an immutable protocol field and
    > have middleboxes rewriting it.

This is my take.
Case 1:  packet is within the LLN.  No issue; the sender sets the flow label,
     and we know (by design) that there aren't any (non-RPL) middle boxes
     that need to rewrite it.

Case 2: the packet has to leave the LLN, travel across the Internet, and
     enter another LLN.
     Here the arguments about the LLN being a kind of virtual host from
     the document are relevant.  The flow label, when it crosses the
     Internet, would be immutable.  Prior to this document, the flow label
     would have been compressed out, been zero, and the DODAG root ought to
     have set it in some consistent fashion anyway.

--
Michael Richardson <mcr+IETF@sandelman.ca>ca>, Sandelman Software Works
 -= IPv6 IoT consulting =-