[babel] source sub-tlv

[Matthieu Boutier <[e-mail]>]

Hello,

Here is my code for source-specific extension of Babel using sub-TLV.

    https://github.com/boutier/babeld/tree/dev

* Packet format

The sub-TLV format is [ type | length | src-plen | src-prefix].  For now,
I use the value 250 for the sub-tlv source prefix.

* Source-specific wildcard requests

At this point, wildcard requests were treated separately.  Legacy
wildcard requests send classical routes only, and source-specific
wildcard requests send specific routes only.  The objective was to
let unchanged the behaviour "send routes specified by 6126 on a 6126's
request".  To have all routes, you had to send one wildcard request and
one wildcard source-specific request.

The current implementation does not change this behaviour.  To have all
routes, you must send one wildcard request (wildcard request without
source sub-TLV) and one source-specific wildcard request (request with
source sub-TLV).

If we keep this behaviour and mix tos-specific routes, we will have
to send 4 wildcard requests to have all routes.  I see two reasonable
options:

  - only keep (legacy) wildcard requests, and reply with a full dump.

  - send one request with all sub-TLVs you know but without mandatory
    bit, and reply to all options you know about.

The second is slightly more complex to implement, but may reduce
overhead when a legacy implementation requests a dump to an extended
one.  It also implies that mandatory and non-mandatory extension shares
the same space.

You may also want to give guidelines for futures extensions in 6126bis
about this kind of problems.

Any thoughts?

Matthieu