Ethernet - speed and duplex settings on an ISR4431

When setting up the speed and duplex settings on a Cisco ISR4431, the configuration parameters must be set in a particular order.

First of all, the interface itself must be up. If it is not, the speed and duplex options are not made available to you. If you try to configure them, you will get an error message similar to the following:

% Invalid input detected at '^' marker

Secondly, once the interface is up, you must first follow these steps in this order:

1. Ensure that the interface has been set to negotiation auto
2. Then set the interface to no negotiation auto to disable the auto-negotiation.
3. Finally, set the speed and duplex settings that you desire.

Other devices may have similar processes that must be followed, however, this has been confirmed for the ISR4431.

Links:

https://forum.networklessons.com/t/interface-speed-and-bandwith/15285/7?u=lagapidis

https://community.cisco.com/t5/routing/duplex-and-speed-commands-missing-isr-4331/td-p/3392703

https://www.cisco.com/c/en/us/support/routers/4441-x-integrated-services-router-isr/model.html