This selects the Layer 2 protocol used at the circuit's second (destination) endpoint, mirroring circuitEndPoint1Protocol but independently settable, meaning this circuit's two ends do not have to use the same protocol. This independence matters operationally because it lets this device support protocol-translating circuits -- for example, an Ethernet access circuit that terminates on an ATM backbone port -- and this field is what tells the device how to parse circuitDestConnectionID for that far end. Setting this to frameRelay(2) while circuitEndPoint1Protocol is ethernet(1) would configure a circuit bridging an Ethernet-side VLAN to a Frame Relay-side DLCI.