Cisco 8851 auto negotiates at 100mb on 3850 & 3750 switches.

Steve W · ‎03-03-2023

We have Cisco 8851 phones that are auto negotiating at 100mb connection instead of 1000. This is happening on both 3750X and 3850 switches (both have gig ports). I did a shut, no shut on a few of the ports and some of the phones did register at 1000mb. However several of the phones are staying at 100. What could be causing this behavior?

MHM Cisco World · ‎03-03-2023

if the Phone not support autonego then the SW will select 100mb by default
so solution is
disable autonrgo and then hardcore Speed

Leo Laohoo · ‎03-03-2023

@Steve W wrote:
However several of the phones are staying at 100.

Check the config of the switch ports.

Check the length of the cable run.

NOTE: Do not make any attempts to perform a TDR using the 3850.

Jonathan Schulenberg · ‎03-05-2023

Along the lines of what Leo said: old/bad cabling or terminations would be my leading suspect. Does this happen when phones are directly connected to the switch new/known good patch cables?