Subject: I-D Action:draft-ietf-6man-exthdr-02.txt

From: [email-masked]
Date: Mon, 14 Mar 2011 15:30:06 -0700

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the IPv6 Maintenance Working Group of the IETF.

	Title           : An uniform format for IPv6 extension headers
	Author(s)       : S. Krishnan, et al.
	Filename        : draft-ietf-6man-exthdr-02.txt
	Pages           : 6
	Date            : 2011-03-14

In IPv6, optional internet-layer information is encoded in separate
headers that may be placed between the IPv6 header and the transport
layer header.  There are a small number of such extension headers
currently defined.  This document defines a format for defining new
IPv6 extension headers.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ietf-6man-exthdr-02.txt

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

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From: John Leslie <[email-masked]>
Date: Mon, 14 Mar 2011 18:55:26 -0400

> currently defined.  This document defines a format for defining new

   I notice that Section 4 calls for TLV:
] 
] 4. Proposed IPv6 Extension Header format
] 
]  This document proposes that all IPv6 extension headers be encoded in
]  a consistent TLV format so that it is possible for nodes to skip over
]  unknown extension headers and continue to further process the header
]  chain.

   But I don't see the equivalent of Section 4.2 of RFC 2460, specifying
the TLV format.

   What am I missing?

--
John Leslie <[email-masked]>

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From: Suresh Krishnan <[email-masked]>
Date: Mon, 14 Mar 2011 20:14:47 -0400

Hi John,

>    But I don't see the equivalent of Section 4.2 of RFC 2460, specifying

The T is the "Next Header", the L is the "Hdr Ext Len" and V is the 
"Header Specific Data" as specified in the figure in Section 4 of the draft.

Thanks
Suresh

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From: John Leslie <[email-masked]>
Date: Tue, 15 Mar 2011 09:25:39 -0400

> "Header Specific Data" as specified in the figure in Section 4 of the

   Well, of course "Next Header" _isn't_ the Type of this option (rather
it's the Type of the next option).

   And the "Hdr Ext Len" isn't a particularly intuitive coding of Length
either...

   IMHO, referring to this format as "TLV" is unnecessarily confusing.

   Also IMHO, if we do define another Extension Header, it's likely we'll
want to make it expandable using the TLV format we _are_ familiar with.

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From: Suresh Krishnan <[email-masked]>
Date: Tue, 15 Mar 2011 09:58:11 -0400

Hi John,

>    And the "Hdr Ext Len" isn't a particularly intuitive coding of Length

Yep. You are right on both counts, but I am not sure how we can change 
this. We cannot chain the headers without the T being in the *previous* 
header. I think the best we can do is to refrain from calling this TLV 
like you said.

>    IMHO, referring to this format as "TLV" is unnecessarily confusing.

OK.

> want to make it expandable using the TLV format we _are_ familiar with.

Do you mean inside the Header Specific data? If so, yes, that makes 
perfect sense.

Thanks
Suresh

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From: "Hing-Kam (Kam) Lam" <[email-masked]>
Date: Tue, 15 Mar 2011 20:07:43 +0530

I am forgetting what the resolution was on the Hdr Options that were
defined in the -01 version. I find those missing here, so i assume
that they have been intentionally dropped out. I was personally in
favor of those and didnt see too much harm in keeping them.

Other than the small nit above, the current version looks good.

Kam

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From: Suresh Krishnan <[email-masked]>
Date: Tue, 15 Mar 2011 15:26:54 -0400

Hi Kam,

> favor of those and didnt see too much harm in keeping them.

Correct. They were intentionally dropped since there was no consensus to 
keep them. I will try to summarize the current status at the Prague 
meeting and see how to proceed further.

Thanks
Suresh

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From: John Leslie <[email-masked]>
Date: Tue, 15 Mar 2011 16:15:39 -0400

> header. I think the best we can do is to refrain from calling this TLV 

   That would satisfy me...

   But, the 2460 section 4.2 TLV also defines four actions when a Type
isn't recognized (skip and three cases of discard). exthdr-02 gives
us no way of defining skip-vs-discard.

   I think some mention of this issue would be wise. It appears, at
first blush, that you intend for a middlebox to skip over these
prospective extension headers, whereas 2460 calls for dropping the
packet.

   I'm not prepared to say what the resolution may be; I just think
it deserves some text (even if only to say, "Beware!").

---

From: Suresh Krishnan <[email-masked]>
Date: Tue, 15 Mar 2011 16:23:07 -0400

Hi John,

> prospective extension headers, whereas 2460 calls for dropping the

Right. These behavior flags were added in version -01 of the draft (the 
previous version) due to a apparent consensus at the physical wg meeting 
but this change has been rolled back in version -02 due to lack of 
consensus in the mailing list.

> it deserves some text (even if only to say, "Beware!").

Let's see if we can make some progress at the next meeting.

Thanks
Suresh