Re: [netmod] question regarding IPv6 address format / canonical

[Ladislav Lhotka <[e-mail]>]

Hi Mikael,

On Fri, 2018-12-07 at 09:20 +0100, Mikael Abrahamsson wrote:
> Hi,
> 
> we've had an interesting interop problem, and we don't know if this is a 
> client, server, or just interop problem. However, I thought I'd bring it 
> to the attention here.
> 
> The server produced an output that was in the format of:
> 
> 2a00:db8:1:2:3::5:0

Correct - this is the canonical value.

> 
> When the client then asked for information about this object it used:
> 
> 2a00:db8:1:2:3:0:5:0
> 
> The netconf server then returned no answer, because it didn't consider 
> these to be the same (string match).

This is a bug in server implementation.

> 
> I have included what I think is relevant text below, it seems the client 
> reformatted the address into canonical format. However, the description 
> below seems to indicate that all those IPv6 types are ok. If the server 
> must use canonical format, is there a MUST somewhere that says so?
> 
> What does it mean that something is a "canonical format"?

It is the value that the server (conceptually) uses internally. See sec. 9.1 in
RFC 7950.

Lada

> 
> https://tools.ietf.org/html/rfc6021
> 
> typedef ipv6-address {
>       type string {
> ....
>       }
>       description
>        "The ipv6-address type represents an IPv6 address in full,
>         mixed, shortened, and shortened-mixed notation.  The IPv6
>         address may include a zone index, separated by a % sign.
>         The zone index is used to disambiguate identical address
>         values.  For link-local addresses, the zone index will
>         typically be the interface index number or the name of an
>         interface.  If the zone index is not present, the default
>         zone of the device will be used.
> 
>         The canonical format of IPv6 addresses uses the compressed
>         format described in RFC 4291, Section 2.2, item 2 with the
>         following additional rules: the :: substitution must be
>         applied to the longest sequence of all-zero 16-bit chunks
>         in an IPv6 address.  If there is a tie, the first sequence
>         of all-zero 16-bit chunks is replaced by ::.  Single
>         all-zero 16-bit chunks are not compressed.  The canonical
>         format uses lowercase characters and leading zeros are
>         not allowed.  The canonical format for the zone index is
>         the numerical format as described in RFC 4007, Section
>         11.2.";
>       reference
>        "RFC 4291: IP Version 6 Addressing Architecture
>         RFC 4007: IPv6 Scoped Address Architecture
>         RFC 5952: A Recommendation for IPv6 Address Text Representation";
>     }
> 
> 
-- 
Ladislav Lhotka
Head, CZ.NIC Labs
PGP Key ID: 0xB8F92B08A9F76C67