Re: [Cbor] Supporting IPv6 Link-Local with scope (was Re: Éric Vyncke's Discuss on draft-ietf-cbor-network-addresses-09: (with DISCUSS and COMMENT))

["Eric Vyncke (evyncke)" <[e-mail]>]

Michael

The problem is indeed solvable.

My own take would be not to use ifIndex (for the reasons you just explained) also it could be confusing with another encoding as both (length & ifindex) are uint...

As I wrote in my ballot, an alternative (not so nice though) would be to clearly state that the encoding is not applicable to LLA + scope

-éric

On 05/10/2021, 20:55, "Michael Richardson" <[e-mail]> wrote:


    Captured as issue:
       https://github.com/cbor-wg/cbor-network-address/issues/12

    Éric Vyncke via Datatracker <[e-mail]> wrote:
        > == DISCUSS ==

        > Generic comment how are link-local address (LLA) with scope encoded ? I would
        > expect CBOR to work also on LLA only networks... At the bare minimum, please
        > state that link-local addresses cannot be encoded with their scope, hence, they
        > cannot represent an interface.

        > -- Section 3.1.3 --
        > How can 2 valid link-local addresses (fe80::1%eth0, fe80::1%eth1) can be
        > represented in order to identity two interfaces ?

    There are three kinds of things encoded:
          a) addresses.
          b) prefixes
          c) interface definitions

    For (b) and (c), we could easily entertain (and did we discuss this in the
    thread that was CC'ed to 6man?) adding a third element to the array to store
    the interface ID.
    For (a), I'm not sure what we can do to add the interface ID, but see below.

    That's kinda the easy part.
    The hard part is deciding how to encode the scope.
    The simplest is as an integer, being the ifindex.

    CBOR makes that easy and efficient, and many systems don't have more than 24
    interfaces.  However, on systems where interfaces come/go a lot, the ifindex
    often increments anyway.  Using the ifindex is probably clearer on most any
    system than a string which can change, but it does change from one boot to
    another.
    While the ifindex is system specific and has no outside meaning, the purposes
    where I imagine this being used would be in some system specific container.
    (My use case, which drove me to do this, actually probably needed scope-id)

    One way to do (a) could be to append to the IPv6 string.
    Another way would be not to bother, to always use the interface definition
    when a IPv6-LL is needed.  Whether the length is 0, 128, or the actual
    interface prefix (probably 64) is something we could specify.

    --
    Michael Richardson <[e-mail]>   . o O ( IPv6 IøT consulting )
               Sandelman Software Works Inc, Ottawa and Worldwide