This is the reverse-direction counterpart to cktBe, defining how much excess or uncommitted traffic the network will still attempt to carry in the direction opposite to the circuit's primary flow, again defaulting to the port's ifSpeed if the admin doesn't explicitly configure it. For example, an admin who set a conservative cktRCir for a lightly-used upstream direction should double check cktRBe isn't silently left at a high ifSpeed default that would let that direction burst far beyond what was actually intended.