Re: [tram] SSODA in TURN-bis

I promised I would write up a summary of the current mechanism, and what we
could do instead, so here goes:

The currently documented mechanism is to send two R-A-F attributes in the
request, and get back either a single address (from legacy servers), v4 +
v6 addresses (from new servers), a single address + a 0.0.0.0/:: (for new
servers that only support one address family), or an error-code (to
indicate complete failure).

At the time, there were 2 concerns listed, namely:
1) sending multiple R-A-Fs is undefined behavior; old (6156) servers may
fail the request completely, or do other weird things.
2) using 0.0.0.0/:: to indicate partial success is somewhat unclean;
specifically, detailed error information cannot be included.

I also thought of a 3rd problem:
3) an old(5766) server may fail the request completely, due to the fact
that R-A-F is comprehension-required. Thus an extra roundtrip may be needed
in this case, negating one of the benefits of SSODA.

I think the ideal solution to #1/#3 is to add a new OPTIONAL-ADDRESS-FAMILY
attribute, identical to R-A-F but comprehension-optional, where multiple
values are explicitly supported. Old servers can safely ignore this and
will return IPv4 (solving #3), while new servers can process this to return
multiple XOR-RELAYED-ADDRESSes in the response.
#2 is not a serious issue, but it could easily be solved by defining a new
ADDRESS-ERROR-CODE as follows:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Address Family                |  Rsvd  |Class|     Number    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      Reason Phrase (variable)                                ..
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Then a server could return a normal IPv4 address, but a error code for
IPv6 with either 440 (unsupported address family) or 508 (insufficient
capacity) or some other TBD error.

I advocate we do the OPTIONAL-ADDRESS-FAMILY attribute as it is simple
and prevents potential interoperability problems with old servers. I
could go either way on ADDRESS-ERROR-CODE.

On Wed, Jan 7, 2015 at 6:02 PM, Tirumaleswar Reddy (tireddy) <
tireddy@cisco.com> wrote:

>  Hi all,
>
>
>
> We are working on incorporating RFC6156 and SSODA into TURN-bis. During
> IETF-91 meeting there was discussion if the technique proposed in
> https://tools.ietf.org/html/draft-martinsen-tram-ssoda-01 would break
> existing TURN server implementations.  Pal had mentioned testing with four
> implementations and did not face any problem.
>
>
>
> Please let us know if there are any concerns with the existing proposal of
> conveying two REQUESTED-ADDRESS-FAMILY attributes with different attribute
> values in Allocate request ?
>
>
>
> Cheers,
>
> -Tiru
>
> _______________________________________________
> tram mailing list
> tram@ietf.org
> https://www.ietf.org/mailman/listinfo/tram
>
>