[Cbor] changes in draft-ietf-cbor-network-addresses-05.txt

Michael Richardson <mcr+ietf@sandelman.ca> Mon, 12 July 2021 11:40 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
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Subject: [Cbor] changes in draft-ietf-cbor-network-addresses-05.txt
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internet-drafts@ietf.org wrote:
    >         Title : CBOR tags for IPv4 and IPv6 addresses and prefixes
    > Authors : Michael Richardson Carsten Bormann
    > draft-ietf-cbor-network-addresses-05.txt Pages : 8 Date : 2021-07-12

    > Abstract: This document describes two CBOR Tags to be used with IPv4
    > and IPv6 addresses and prefixes.

    > The IETF datatracker status page for this draft is:
    > https://datatracker.ietf.org/doc/draft-ietf-cbor-network-addresses/

    > There is also an HTML version available at:
    > https://www.ietf.org/archive/id/draft-ietf-cbor-network-addresses-05.html

    > A diff from the previous version is available at:
    > https://www.ietf.org/rfcdiff?url2=draft-ietf-cbor-network-addresses-05

The major differences since -04 is that we now have three forms:

1) IPv4 or IPv6 address.
2) IPv4-prefix/len or IPv6-prefix/len
new: 3) IPv4-addr/len or IPv6-addr/len

The difference between (2) and (3) is that (2) is just the prefix, and the
bits to the right MUST be zero, and MAY be omitted. (A bit win for IPv6/32 or
Ipv6/48s..).
In the case of (3), this is more of an interface definition, like:
   2001:db8::1234/64  the "::1234" is to the right of the /64.
   192.0.1.4/24     ".4" is to the right of the /24, and is the interface definition.

Cases (2) and (3) are distinguished by order of data vs prefix.
(2) is:   [64, h'20010db8']
(3) is:   [h'20010db8_00000000_00000000_00001234', 64]
We can do this in CBOR, because it is self-describing.
Note that (2) is much shorter than (3), because trailing zeroes are omitted.
(3) is always 18 or 19 bytes long. (1 byte for CBOR array prefix)

Prefix longer than 24 require two bytes to encode the integer.
(I guess we could have made the prefixlen be length-24, and then up to /48
would fit into a single byte integer.  We could also have made the negative
integers represent multiples of -4 perhaps)

I don't personally have a use case today for (3), but there were not many
objections to including it.

--
Michael Richardson <mcr+IETF@sandelman.ca>   . o O ( IPv6 IøT consulting )
           Sandelman Software Works Inc, Ottawa and Worldwide