Is manually setting port speed to 1000 backwards compatible?

[getaway51]

Hi, 

May I know if settings the port manually to settings below will fall back to auto-negotiated speed of 100Mbps if 1Gbps doesn't take effect?

Currently the port is auto-negotiate. I am worried that if it the port works only on 1Gbps after i changed the settings remotely, then the link might not comes up, hence losing connectivity.  Unless even after i set speed to 1000, the port still can auto-neg to 100 if 1000 fails.

interface TenGigabitEthernet1/0/1

speed 1000

[Giuseppe Larosa]

Hello,

if you set manually the speed there is no fallback to autonegotiation, if the other side is not able to negotiate and tries to run at 100 Mbps your link will go down

>> I am worried that if it the port works only on 1Gbps after i changed the settings remotely, then the link might not comes up, hence losing connectivity.

This is what can happen.

Keep the current configuration if there is no real issue with the device connected on the other side.

Only really old devices have NIC that do not work well with autonegotiation. With these exceptions the general best practice is to use autonegotiation.

Hope to help

Giuseppe

[Leo Laohoo]

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@getaway51 wrote:

interface TenGigabitEthernet1/0/1

speed 1000

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Are you talking about the command "speed auto 10 100"?

Another thing, if the port CAN run 1000 Mbps why not set it to auto-negotiate?

Hard coding of the speed ... that's a very, very "old school".  I wish I could use "correct" and "old school" together.  

Hard coding of the speed and duplex ... not recommended.

[Joseph W. Doherty]

BTW when making remote configuration changes, where you might lose access to the device due to those changes, a timed reload can save your bacon. Also when making configuration changes that change the remote port you're working through, sometimes you need to save them as a file on the remote device and then have them applied to the running configuration with one command.