How to use ipmitool bridging

I read the bridging section in 'man' several times but it might as well be written in Greek (or perhaps I fundamentally misunderstand what it is).

Suppose that I have two server nodes (A and B), each one has an IPMI controller.

Nodes are connected to the network and I can access them remotely.

Their IPMI controllers are also connected to the network, but they sit on a different switch, and, for some reason (probably because network admins screwed up), I can't reach them. (I can do 'sudo ipmitool lan print' on A, and it tells me the IP address of the corresponding controller, but I can't communicate with that IP.)

Node B suffers a failure and I need to reboot it. I know the IP of its IPMI controller.

How do I tell the controller of A to communicate a reboot command to the controller of B?

From what I understand, the "bridging" feature in ipmitool has nothing to do with accessing other controllers over the network – its purpose is to access controllers available on the I2C bus through an ICMB bridge (e.g. if you have a "chassis" IPMI controller which directly connects to "blade server" IPMI controllers via I2C).

To reach another IPMI controller over LAN, you will actually need to reach that LAN from the host.