Autonegotiation Status/Error Table
Autonegotiation is optional for Gigabit Ethernet connections. This can lead to one side having autonegotiation on, while the other side has autonegotiation off. When this happens, one side can see their port as up, while the other sees their port as down. This leads to confusion and unnecessary troubleshooting.
The following table shows all the possible ways in which a gigabit connection can be set.
|Side A autonegotiation| Side B autonegotiation| Side A Sees | Side B Sees| Link | |on | on | up | up | yes| |on | off | down | up | no | |off | on | up | down | no | |off | off | up | up | yes |
As you see, both sides of the connection must have a matching autonegotiation setting for there to be link. If oneside is hard set and the other has autonegotiation on, then link will not be established, but one side of the connection will show their port as up.
This problem is mostly seen with fiber connections. Copper tends to still establish link, even if autonegotiation settings do not match.
This problem goes away completed with 10 gigabit and above speeds and autonegotiation is part of the protocol and cannot be turned off.