The speed mismatch will cause the Fa0/1 interfaces to be down. Switch ports that are manually configured to use different speeds will cause speed mismatches. To prevent a speed mismatch from occurring, you should ensure that one or both sides of a link are set to autonegotiate and that the two interfaces have at least one data transmission speed in common. The speed mismatch will not cause a switching loop. When a speed mismatch occurs, neither interface will establish a link. Therefore, a switching loop will not occur, because data cannot flow through the port.

The Fa0/1 interfaces on SwitchA and SwitchD are manually configured with different duplex modes. However, a duplex mismatch will not cause the interfaces to be down? if there were no speed mismatch, the interfaces would be up and the line protocol would be up. A duplex mismatch can cause collisions, alignment errors, intermittent connectivity, and switching loops. Therefore, if there were no speed mismatch, a switching loop could occur because of the duplex mismatch. Data will not be sent between SwitchA and SwitchD at 10 Mbps. To enable data to flow between SwitchA and SwitchD at 10 Mbps, you should issue the speed 10 command on the Fa0/1 interface of SwitchA. Alternatively, you could configure the Fa0/1 interface of SwitchA to autonegotiate speed and duplex settings. To enable data to flow between SwitchA and SwitchD at 100 Mbps, you should issue the speed 100 command on the Fa0/1 interface of SwitchD. You should not configure SwitchD to autonegotiate speed and duplex settings, because a port configured to transmit at 10 Mbps or 100 Mbps defaults to halfduplex mode, which would cause a duplex mismatch.