[Babel-users] Babel ignoring tunnel interfaces

[Juliusz Chroboczek]

I'm receiving e-mail from users complaining that Babel is ignoring
their tunnel interfaces.

For an interface to be usable by Babel, it must:

  - support IPv6;
  - have a link-local IPv6 address.

The first point means that you cannot run Babel over e.g. IPIP
tunnels; use GRE tunnels instead.  Note that this remains true even on
a pure IPv4 network -- Babel is a hybrid protocol (IPv4 and IPv6), and
Babel routing information is exchanged over IPv6, even in a pure IPv4
network.

The second point is more tricky.  Linux will autoconfigure a link-
local address on broadcast interfaces, but will not necessarily do it
on point-to-point interfaces (there are some exceptions).  Check if
you have a link-local address:

  $ ip -6 addr show alpha
  5: alpha at eth0: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1476 
      inet6 fe80::d8f0:3587:f850:4a99/128 scope link 
         valid_lft forever preferred_lft forever

If you have a line that says ``inet6 fe80::... scope link'', you're
fine.  If you don't, you'll need to say something like

  ip -6 addr add (ahcp-generate-address fe80::)/64 dev whatever

You'll find the ahcp-generate-address utility in the ahcpd package.

All of this is described in Babel's README file.  If it's not clear
enough, I'll be grateful for any patches.

                                        Juliusz