The Complete Ethernet Duplex Autonegotiation Scenarios

Side A (10/100Mbps)	Side B (10/100Mbps)	Side A Speed / Duplex	Side B Speed / Duplex
auto/auto	auto/auto	100/full	100/full
auto/half	auto/auto	100/half	100/half
auto/full	auto/auto	100/full	100/full
10/auto	auto/auto	10/full	10/full
10/half	auto/auto	10/half	10/half
10/full	auto/auto	10/full	10/half
100/auto	auto/auto	100/full	100/full
100/half	auto/auto	100/half	100/half
100/full	auto/auto	100/full	100/half

Side A (10/100Mbps)	Side B (10/100/1000Mbps)	Side A Speed / Duplex	Side B Speed / Duplex
auto/auto	auto/auto	100/full	100/full
auto/half	auto/auto	100/half	100/half
auto/full	auto/auto	100/full	100/full
10/auto	auto/auto	10/full	10/full
10/half	auto/auto	10/half	10/half
10/full	auto/auto	10/full	10/half
100/auto	auto/auto	100/full	100/full
100/half	auto/auto	100/half	100/half
100/full	auto/auto	100/full	100/half

Side A (10/100/1000Mbps)	Side B (10/100Mbps)	Side A Speed / Duplex	Side B Speed / Duplex
auto/auto	auto/auto	100/full	100/full
auto/half	auto/auto	N/A [1]	-
auto/full	auto/auto	100/full	100/full
10/auto	auto/auto	10/full	10/full
10/half	auto/auto	10/half	10/half
10/full	auto/auto	10/full	10/half
100/auto	auto/auto	100/full	100/full
100/half	auto/auto	100/half	100/half
100/full	auto/auto	100/full	100/half
1000/auto	auto/auto	-LINK DOWN-	-LINK DOWN-
1000/half	auto/auto	N/A [2]	-
1000/full	auto/auto	-LINK DOWN-	-LINK DOWN-

Side A (10/100/1000Mbps)	Side B (10/100/1000Mbps)	Side A Speed / Duplex	Side B Speed / Duplex
auto/auto	auto/auto	1000/full	1000/full
auto/half	auto/auto	N/A [1]	-
auto/full	auto/auto	1000/full	1000/full
10/auto	auto/auto	10/full	10/full
10/half	auto/auto	10/half	10/half
10/full	auto/auto	10/full	10/half
100/auto	auto/auto	100/full	100/full
100/half	auto/auto	100/half	100/half
100/full	auto/auto	100/full	100/half
1000/auto	auto/auto	1000/full	1000/full
1000/half	auto/auto	N/A [2]	-
1000/full	auto/auto	1000/full	1000/full

[1]

C2960G(config)#int gi0/1
C2960G(config-if)#duplex half

% Duplex cannot be set to half when speed autonegotiation subset contains 1Gbps

C2960G(config-if)#

[2]

C2960G(config)#int gi0/1
C2960G(config-if)#speed 1000
C2960G(config-if)#duplex half
Gigabit port is restricted to full duplex
C2960G(config-if)#