cmEthernetTrafficPortConfigSpeed is a read-write setting used to configure the desired speed of this Ethernet port. An administrator sets this to force a specific rate or auto-negotiation behavior appropriate for what is plugged into the port, since a mismatch with the connected device's capabilities prevents the link from coming up. For example, connecting a legacy 100Mbps device to a port capable of 1Gbps would require lowering this configured speed to 100Mbps rather than leaving it at a gigabit setting the far end cannot negotiate.