A read-write value, in PDUs per second and defaulting to 0 (no limit), setting the rate at which the interface starts dropping tunneled PDUs for a given protocol, and which cannot exceed the paired shutdown threshold. This gives an admin a rate-limiting safeguard against tunneled protocol traffic, such as a BPDU storm, overwhelming the interface, discarding excess PDUs once the configured rate is exceeded rather than passing them all through. An admin protecting against a misbehaving downstream switch flooding STP BPDUs might set this to 100 PDUs/sec so excess tunneled BPDUs get dropped rather than saturating the tunnel.