[babel] Babel over DTLS and UDP ports

[David Schinazi <[e-mail]>]

Hi Babel enthusiasts,

As currently documented
<https://tools.ietf.org/html/draft-ietf-babel-dtls-04>, Babel over DTLS
uses two UDP listening ports:
- 6696 for regular unencrypted Babel packets
- a separate port (number TBD) for Babel-over-DTLS packets

When the authors requested the new port from IANA, we received some
pushback. The position of the IANA port expert was that UDP ports are a
scarce resource and they strongly prefer to not allocate them unless it is
necessary. So the question for the Babel WG is: is the separate port
necessary?

One possible solution could be for us to have unencrypted packets and DTLS
packets share the same port. For that we can leverage the fact that all
Babel packets start with a first byte set to 42, and say that DTLS packets
use the same port, prefixed with 43 instead of 42.

What are people's thoughts? In particular, if you have an implementation of
Babel over DTLS (or if you are considering building one), do you think the
proposal above could be fit into your implementation?

Thanks,
David