While reading comp.unix.solaris, I noticed Rick Jones posting this amusing table that explains the outcome of duplex negotiation settings.

While there’s a chuckle here, it is possibly the most concise explanation of the interaction between NIC configurations I’ve seen in a long time.

The rule is simple - either both ends of a connection are Autonegotiated, or both ends have their duplex fixed. We used to see a lot of fights between Sun hosts and Cisco switches, often because the default switch template used by network groups with to disable negotiation and lock the duplex at full. The host tried to negotiate, came up with half duplex and there was misery until somebody write a scripting using ndd to include in the boot sequence. Horrible.

Fortunately, gigabit ethernet mandates use of autonegotiation, which gets rid of the whole horror. If you’re still dealing with 100Mbit though, enjoy the table.