Auto-negotiation of transmission speed and duplex mode is mandatory for 1000 BASE-T gigabit Ethernet over copper. To avoid duplex mode mismatches and other interoperability problems, ensure that auto-negotiation is configured on the Network Interface Cards (NICs) and the switch. Configure the NICs and the switch with matching modes. If you disable auto-negotiation and configure the NICs to full-duplex mode or half-duplex mode then the switch must also have auto-negotiation disabled and be set to the matching full-duplex mode or half-duplex mode. For more information, see the configuration procedures your server and switch manufacturer provides.