Configuring Auto-Negotiation

For Cisco switches, auto-negotiation is enabled by default. You can configure the speed and duplex mode manually with the speed and duplex interface commands in IOS.

You cannot set the duplex mode without first setting the speed. The switch will complain if you attempt to do so:

2950(config-if)#duplex half
Duplex can not be set until speed is set to non-auto value

To set the speed of the interface, use the speed command. If the interface has previously been configured, you can return it to auto-negotiation with the auto keyword:

2950(config-if)#speed ?
  10    Force 10 Mbps operation
  100   Force 100 Mbps operation
  auto  Enable AUTO speed configuration

Once you've set the speed, you can set the duplex mode to auto, full, or half:

2950(config-if)#duplex ?
  auto  Enable AUTO duplex configuration
  full  Force full duplex operation
  half  Force half-duplex operation

Get Network Warrior now with the O’Reilly learning platform.

O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.

Start your free trial