Re: [spring] Typo correction Re: Question from SPRING regarding draft-filsfilscheng-spring-srv6-srh-compression

On Thu, Oct 14, 2021 at 2:07 PM Brian E Carpenter
<brian.e.carpenter@gmail.com> wrote:
>
> On 14-Oct-21 22:41, Ted Hardie wrote:
> > On Wed, Oct 13, 2021 at 9:28 PM Brian E Carpenter <brian.e.carpenter@gmail.com <mailto:brian.e.carpenter@gmail.com>> wrote:
> >
> >
> >
> >     Including semantics *of any kind* in an IP address is a very fundamental
> >     change to the concept of IP.<https://www.ietf.org/mailman/listinfo/ipv6>
> >
> >
> > Would you mind elaborating what you mean by semantics in the statement above?  Clearly there are semantics in things like the IPv4 multicast and experimental address ranges (aka "Class D" and "Class E"); especially for the multicast case, the very fundamental semantics of the distribution are signalled using the address and there has been significant deployment using those semantics.  Isn't that semantics in the meaning above?
>
> Yes, I should have restricted my remark to *unicast* addresses. But there
> is a difference, I think, between semantics that describe the *type of address* and semantics that actively describe *what the recipient is going to do*. It's the latter that I was getting at.
>
Brian,

Joel's description is very good, and it makes me think that this
mechanism is best described as yet another form of NAT. Similar to a
NAT device, these devices are rewriting destination addresses per some
algorithm which is not necessarily exposed to the outside world. In
both NAT and Sid compression, packets are being routed to some
intermediate node which is performing address translation and
forwarding. The Sid compression method has the advantage that the
translation is  stateless. While SId compression is explicit as
encoded in the destination address set by the sender, it seems like
Sid compression would still be transparent to any intermediate node
that's not the destination address-- that would include the Internet
in packets that were leaked.

Given that NAT seems to work okay, I don't immediately see how SId
compression would be any more of a problem :-)

Tom

> (This applies to Carsten's comment too. Port numbers or multiple addresses per host are not actively describing what the recipient will do; they're just numbers.)
>
> Also, I tried not to express shock and horror at the notion of semantics in address, but concern about how this will impact existing hardware and software.
>
> >
> > Thanks for any clarification,
> >
> > Ted
> >
>
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