Subject: [6lo] mic comment on IPv6 EID 3bits for Extension Headers and IANA 255 possible extension headers

From: Alexandre Petrescu <[email-masked]>
Date: Thu, 5 Nov 2015 10:57:47 +0900

Hello,

I would like to comment with respect to enconding IPv6 EID (Extension 
header ID?).

I am not sure which document defines the EID?  The slide shows 3 bits 
reserved to encode Extension Header types.

But 3 bits can not accommodate 255 possible Extension Headers as listed 
at IANA:

http://www.iana.org/assignments/ipv6-parameters/ipv6-parameters.xhtml

For example, one needs to encode at least the HIP extension header, 
Shim6 extension header, "experimentation and testing extension header".

Alex

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From: Oleg Hahm <[email-masked]>
Date: Thu, 5 Nov 2015 14:49:01 +0900

Hi Alex,

> reserved to encode Extension Header types.

IPv6 Extension Header Compression ID (EID) is defined in RFC6282 (IPHC):
https://tools.ietf.org/html/rfc6282#section-4.2
 
> But 3 bits can not accommodate 255 possible Extension Headers as listed at
> IANA:
> 
> For example, one needs to encode at least the HIP extension header, Shim6
> extension header, "experimentation and testing extension header".

To my understanding any extension header that has no LOWPAN_NHC encoding
defined in this or any other corresponding RFC has to follow after any
potentially present encoded NHC header in an uncompressed fashion.

Cheers,
Oleg

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From: Alexandre Petrescu <[email-masked]>
Date: Thu, 5 Nov 2015 16:56:08 +0900

Hi Oleg,

> potentially present encoded NHC header in an uncompressed fashion.

I do not disagree, that is the logical conclusion.  Any such header 
(e.g. shim6) will not be compressed, and supposedly not covered by IPsec 
either if I understand correctly.  There may not necessarily be a 
use-case for e.g. shim6 in 6lo networks anyways.

Alex