Could you give me some hints about multi-bridge scenarios.
You can just set up two "mirrored" bridges.
You have two network interfaces in your bridge?
Set up the mirror bridge so that it has two network interfaces
as well, and connect each of the interfaces to one subnet.
This will work without the need of configuration.
Note: Be sure that you have the spanning tree protocol
enabled.
If you didn't use brctl, this should
be fine, because in Linux, it is on by default.
To check, you could check whether the bridge sends a
packet to 0180c2000000
every 2 seconds.
If it does, the STP is on.
The STP is needed so that only one bridge will be active
at any given time.
Note: To be able to see nicely formatted stp packages in your
network take a look at at the bridge homepage for the patches
to tcpdump.
The "master" bridge will send out STP packets every
2 seconds by default.
The "slave" bridge will receive these packets,
and will notice that the master is still up.
If the slave hasn't received a packet in 20 seconds (max.
message age parameter), it will start the takeover procedure.
From the moment the takeover procedure starts, it will take
about 30 seconds (twice the forward delay parameter) for the
bridge to become fully operational.
Does the STP "heartbeat" mechanism also work
with bridges with more than two cards?
Yes, it works with any number of interfaces.
You can invent bizarre topologies to your heart's desire.
You can use multiple (redundant) bridge-bridge connects,
you can insert loops, whatever.
The STP code will always find the minimal spanning tree.
The bridge code will even deal with the loss of any number
of interfaces.
If there are two redundant bridges with identical connections,
the loss of an interface on one of the bridges will cause the
other bridge to take over forwarding to that specific
interface.
Now isn't that great? :)
How fast does it get up, and what can I do about it?
If you think 50 seconds is too much -- and I guess you
should; alas, the IEEE specs gives us these default values
-- you can tweak these parameters.
If you set the hello time (the STP packet interval) from 2 to 1
second, you can safely set the message age parameter to 4
seconds.
Then you can set the forward delay to 4 seconds, and this will
in total give you a takeover time of ~12 seconds.