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New Member

%CDP-4-DUPLEX_MISMATCH (IP-phone)

Hi! I'm getting this error on an access switch.

%CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/9 (not half duplex), with SEP00141C8Dxxxx Port 1 (half duplex).

Why is the phone port 1 half duplex? Shouldn't the phones be configured as auto-negotiation as default?

Could it be a cabling issue?

Will it affect the throughput / performance on that port?

This is happening with some of my other phones + switches.

5 REPLIES

Re: %CDP-4-DUPLEX_MISMATCH (IP-phone)

Hi! I'm getting this error on an access switch.

%CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/9 (not half duplex), with SEP00141C8Dxxxx Port 1 (half duplex).

Why is the phone port 1 half duplex? Shouldn't the phones be configured as auto-negotiation as default?

Could it be a cabling issue?

Will it affect the throughput / performance on that port?

This is happening with some of my other phones + switches.

Hi,

Have you checked from switch side is auto negotion is configured with the port where ip phone is configured.

HTH


Ganesh.H

New Member

Re: %CDP-4-DUPLEX_MISMATCH (IP-phone)

Hi!

There is nothing configured on the switch-port therefore it should be auto, because the default is auto negotiation.

Normally 100BaseTX is going full duplex and 100 Mbit/s, so why is the phone going down to half duplex?

Hall of Fame Super Gold

Re: %CDP-4-DUPLEX_MISMATCH (IP-phone)

Begin updating phone firmware.

Super Bronze

Re: %CDP-4-DUPLEX_MISMATCH (IP-phone)

Hi

First thing to check is whether the phone has been configured for half duplex - this is a setting configured from the phone itself (via the keypad). You can go into 'settings', then 'network configuration' and scroll down until you see the 'PC' and 'SW' port configurations.

If you are not near the phone you can browse to the phone IP with Internet Explorer and then click 'Network Configuration' on the left. Somewhere in that list should be the configured speed/duplex settings.

If it is configured for auto/auto, then I would check that there are not multiple devices on the affected switch port - for example someone may have inserted a hub or other intermediate device.

Aaron

Please rate helpful posts...

Aaron Please remember to rate helpful posts to identify useful responses, and mark 'Answered' if appropriate!
New Member

Re: %CDP-4-DUPLEX_MISMATCH (IP-phone)

What model switches and phones? What version of IOS are you running? Can you post an excerpt of your config from one of the problem switches?

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