[Babel-users] V4-via-v6 merged into master

[Juliusz Chroboczek]

Dear all,

I've just merged support for v4-via-v6 routing into babeld master.

V4-via-v6 routing is a routing technique that allows routers with only
IPv6 addresses (including link-locals) to forward IPv4 packets.  It
doesn't involve encapsulation (tunnelling), it doesn't involve translation
(NAT), it just works.  For details, please see

  https://datatracker.ietf.org/doc/html/draft-ietf-babel-v4viav6

Short story: v4viav6 is enabled by default if your kernel is recent
enough.  Just upgrade babeld to current master, and you should see your
v6-only routers forward IPv4 packets.  In order to disable announcing of
v4-via-v6 routes, add the following to your configuration file:

    default v4-via-v6 false

Long story.  There are two pieces to v4-via-v6: installing IPv4 routes
with an IPv6 next hop, and announcing such routes.  By default, babeld will:

  - install v4-via-v6 routes on Linux 5.2 and later;
  - announce v4-via-v6 routes on Linux 5.13 and later.

The former behaviour cannot be overridden -- we always install v4-via-v6
routes if the kernel supports them, and (obviously) never do otherwise.
The latter behaviour can be overridden by the interface option 'v4-via-v6'.
Feel free to experiment, but be aware that enabling v4-via-v6 on an older
kernel might create ICMP blackholes.

Please let me know if you feel that it should be possible to completely
disable v4-via-v6 even on newer kernels, and whether you feel that
v4-via-v6 should be disabled by default.  (The "Security Considerations"
section of the draft cited above might be interesting.)

Enjoy,

-- Juliusz