Host Subsystem Location
Figure 121 shows the location of the host subsystem components on the M320 and T320 routers and the T640 routing node.
You can install one or two host subsystems into the midplane from the rear of the chassis. Each host subsystem functions as a unit: the Routing Engine requires the corresponding Control Board to operate, and vice-versa. If the adjacent component is not present, the Routing Engine or Control Board will not function. RE0 installs below CB0, and RE1 installs above CB1 otherwise the circuit will not be connected.
You take the host subsystem offline and online as a unit. Before you replace a Routing Engine or a Control Board, you must take the host subsystem offline. The host subsystem is hot-pluggable.