This read-only OCTET STRING, a variable-length array changeable only by rebooting the ES/1, defines the port types expected for a module; if a port's actual hwPortType doesn't match the corresponding entry here, that port won't be used. An admin uses this to confirm the configured expected port type matches what an installed module's port actually reports. For example, a mismatch between hwDefPortType and hwPortType for port 2 on an IOM would explain why that specific port is being ignored despite the module otherwise functioning.