Re: [Cbor] changes to draft-ietf-cbor-network-addresses-01.txt

Brian E Carpenter <brian.e.carpenter@gmail.com> Tue, 09 March 2021 04:28 UTC

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To: Carsten Bormann <cabo@tzi.org>, Michael Richardson <mcr+ietf@sandelman.ca>
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From: Brian E Carpenter <brian.e.carpenter@gmail.com>
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Date: Tue, 9 Mar 2021 17:28:45 +1300
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Subject: Re: [Cbor] changes to draft-ietf-cbor-network-addresses-01.txt
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On 08-Mar-21 20:53, Carsten Bormann wrote:
> I think prefixes and addresses are completely separate use cases.
> 
> There is rarely a point in suppressing trailing zeroes in an address.
> We shouldn’t burden implementations to cater to this 0.4 % case (probably less in practice).
> 
> Prefixes are different, and they should indeed always be tail-cut.
> (They are usually /64 or shorter, so there is a real win.)

True, but we didn't bother about that in draft-ietf-anima-prefix-management, because it isn't really aimed at constrained devices. It sends the prefix as bytes .size 16
(or bytes .size 4), which makes life easier.
 
> We could imagine an alternate world where IIDs are carefully chosen so that actual addresses have as many trailing zeroes as possible.

We could, but that contravenes the IPv6 privacy recommendations.

> But that’s not what happens today.  If we were to compress inner zero runs (as in “::”), we’d need to give the byte position where that happens (the length would be implied by the length of the remaining byte string).
> I’m not proposing we cater to that.

No, you'd be better inventing a generic "compress zero bytes" mechanism and tag, but would you really want to go there?

    Brian

> 
> Grüße, Carsten
> 
> (The /24 IPv4 example in the draft is wrong.)
> 
>