Subject: (IPng 6692) Re: Last Minute comments on "A Method for the Transmission of IPv6 Packets over ARCnet Networks"

From: [email-masked] (Tim Hartrick)
Date: Wed, 4 Nov 1998 09:13:56 -0800

Ignatios,

> 
> > >    The protocol id used is D4 hexadecimal, the same as for IPv4. IPv6
> > >    packets are recognized by looking at the version number in the high
> > >    half of the first octet of the data, which is 4 for IPv4 and 6 for
> > >    IPv6. This method of distinguishing IPv6 packets was chosen because
> > >    there are only 256 values of ARCnet protocol ids available.
> > 
> > I note that this is inconsistent with the IPng position that all link
> > layer types provide a way to identify IPv6 packets as distinct from
> > IPv4. The above will also make it impossible to implement Header
> > Compression as outlined in draft-degermark-ipv6-hc-06.txt on ARCnet
> > links. Is this a potential problem?
>  
> Currently, there are no plans to implement header compression over ARCnet.
> 
> Rereading the header compression paper, I note that header compression
> is aimed at slow to medium speed point to point style links, with some
> sort of link level negotiation protocol. So it would not be really desirable 
> to implement header compression for ARCnet (at 2.5 MBit/s) (or Ethernet,
> FDDI, Token Ring...)
> Am I correct?
>

Unfortunately, there were other reasons for the IPng WG specifying that the
link-layer provide a mechanism for distinguishing IPv4 from IPv6 packets.

The principle reason was that it was assumed that a large percentage of the
deployed IPv4 implementations would not check the version number.  Indeed,
at the time multiple vendors admitted as much.  This lack of robustness in
deployed IPv4 implementations could lead to problems when IPv6 packets
suddenly start to arrive at those nodes.

Header compression had nothing to do with the issue at the time but it is
an issue now assuming that anyone would be interested in running header
compression over ARCnet.

My preference would be that there be a seperate "Protocol ID" for IPv6 since
our implementation depends on this feature.  I believe other implementations
do as well.

Tim Hartrick
Mentat Inc.
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From: Ignatios Souvatzis <[email-masked]>
Date: Wed, 4 Nov 1998 20:59:42 +0100

> suddenly start to arrive at those nodes.

Ok. ... e.g. all Net/2 derived, unless repaired later. 4.4BSDlite does.
To see how much of a problem this would create, if we dont get a number:
How many of them do have ARCnet support? BSD never had, before NetBSD.

> our implementation depends on this feature.  I believe other implementations

Bob Hinden has offered to ask for one ex officio. Lets wait for the result.

Regards,
	Ignatios Souvatzis