Hello Stewart, Brian and Toerless:

Interestingly RFC 8138 took one step in that direction. Yes you’re going to 
need a new Ethertype but it’s still IPv6 I. That is is expressed as a 
compression not a modification of IPv6.

 In the compressed form the header starts with the next hops, the destination 
and SRH being indiscriminated, the destination is just the first of the list. 
The size is variable but each hop is at most 128 bits. Because the SRH could 
encode SRv6 you can already go a long way with this.

If that can help you do what you want, I m happy to explain more...

Keep safe.

Pascal

Le 2 mars 2021 à 13:33, Stewart Bryant <[email protected]> a écrit :



On 1 Mar 2021, at 20:08, Brian E Carpenter 
<[email protected]<mailto:[email protected]>> wrote:


It would take but a minute to design a longer-address mechanism for IPv6, 
although I don't have space to include it in the margin of this email**. But it 
would take many years for it to be widely implemented and deployed, during 
which time the Internet would be opaque to such addresses.


** Basically, use a prefix such as fb00::/8 to indicate an extended address.

Hi Brian

Basically I think that this fails the backwards compatibility text.

It is perfectly legitimate to write an IPv6 forwarder as follows:

If MACaddress == me and MACtype == IPv6 pass packet to IPv6 forwarder

In IPv6 forwarder:

If version == IPv6 and Hop Limit not exceeded send bytes 24 to 39 to address 
lookup engine

Wait for address result and forward packet accordingly

Except that this forwarder would have sent a bunch of random junk to the ALE 
consisting of some of the SA and maybe some of the DA depending on their sizes.

So to stop an old and legitimately designed parser being fooled you really have 
to use a new MAC type and a new version and as soon as you do that you might as 
well design the packet optimally for the job at hand.

If the IPv6 designers had followed the strategy of both the Ethernet designers 
and the ISO8473 designers and put DA before SA then the elegant approach that 
you and others have  proposed at various times would have worked nicely.

Best regards

Stewart




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