When the autonegotiation of both speed and duplex happens, two rules are
followed: the slowest supported speed is used, and the duplex will be half for
devices that support 10 or 100 Mbps OR full for devices that support only 1000
Mbps. In this case, both the switch and Host A support 10 Mbps, so the speed
would be set to 10 Mbps and the duplex would be set to half.

The Gi0/6 interface shown displays “a-full” and “1000.” This means that the
interface duplex has been automatically negotiated and interface speed has been
manually configured with the speed 1000 command.

Basic Switch Configuration