[Babel-users] Babel and bridged interfaces

[Juliusz Chroboczek]

As you probably know, Babel tries to automatically detect whether an
interface is wired or wireless, and uses a more economic algorithm for
determining link quality on wired interfaces.  The wireless algorithm
works well on wired interfaces, but the wired one won't work well (or
at all) on wireless interfaces.

This behaviour fails in one significant case, when people run Babel on
bridged interfaces, which Babel detects as wired interfaces. According
to the (private) e-mails I'm getting, this is particularly common on
OpenWRT systems, where eth0.0 and wl0 are bridged by default.

I do not recommend running Babel on bridged interfaces, since the
inverse multiplexing caused by the bridge removes some information,
and prevents Babel from dropping the hello interval.  It is better to
remove the bridge and run Babel separately on the underlying
interfaces.  (Of course, this is not possible if you need to forward
broadcast traffic between interfaces.)

On OpenWRT, you will need to edit /etc/config/network, so that it
looks something like

  config interface lan
          option ifname "eth0.0"
          option proto static

  config interface wan
          option ifname "eth0.1"
          option proto static

  config interface wifi
          option ifname "wl0"
          option proto static

In a future version, I'll try to detect bridged interfaces and run the
wireless algorithm on them by default, and provide a means to configure
the algorithm used on a per-interface basis.  If you have any better
ideas, I'm interested.

Regards,

                                        Juliusz

P.S. I prefer correspondence about Babel to go to the list, rather
     than to me personally.