rcRelayShutdownThreshold sets the rate, in PDUs per second (0 to 4096), at which an interface shuts down entirely for a given tunneled protocol, with 0 meaning no limit and the value required to be at least as high as rcRelayDropThreshold. Admins use this as a stronger protective measure than dropping, taking the interface out of service for that protocol if the flood rate becomes severe enough to be considered abnormal. For example, setting rcRelayShutdownThreshold to 500 PDUs/sec shuts the interface down for that protocol if tunneled traffic sustains a rate above 500/sec, well beyond a lower rcRelayDropThreshold of 100.