Hi,

> On 3 Mar 2021, at 12:05, Pascal Thubert (pthubert) 
> <[email protected]> wrote:
> 
> 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.

IMHO, from an architectural point of view I would argue that it is a different 
L3 protocol: different header; different forwarding machinery;

The fact that has been designed to be « compatible » with IPv6, where a simple 
method exists to translate one in the other, basically having a one-to-one 
mapping,  is a different thing. 

Yet, I would also add that the real objective of the discussion is whether or 
not it exists a sufficiently general mechanism that enables the same feature 
(as for RFC 8138)  among different limited domains.

If it exists, what is the general addressing « model » (for lack of a better 
term) that would accommodate such a requirement or allow to create such a 
general solution?

Ciao

L.


> 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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