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New Member

CDP errors with mixing full/half duplex links on switch

We are getting CDP error msgs. complaining that we have full duplex on one switch and half on another.

I'm not sure if no cdp enable will clear up. (will try)

What I'm wondering, is what's "wrong" with mixing full and half on switches?

3 REPLIES
New Member

Re: CDP errors with mixing full/half duplex links on switch

I had this same problem about two or three months ago... You do not want to mix full and half duplex because it will cause lots of ethernet collisions and severly degrade your network performance. However, you will want to look and verify that both sides are set to either full or half and if they are and you are still seeing the the same CDP Duplex Mismatch then check out this link to correct the incorrect error message.

http://www.cisco.com/cgi-bin/Support/Bugtool/onebug.pl?bugid=CSCdp48362&cco_product=IOS&fset=&swver=12.0&keyw=CDP-4-DUPLEX_MISMATCH

If this link doesn't work right, it is bug ID CSCdp48362

Purple

Re: CDP errors with mixing full/half duplex links on switch

You cannot have half/duplex on one end of the link and full/duplex on the other . This configuration will cause all kinds of port errors and will lead to a poorly performing link to say nothing about the cdp errors that you are seeing . If you have full/duplex on one end of the link then you must have full/duplex on the other end . Or you can have both ends set as auto which will autonegotiate the speed and duplex of the ports though the prefered method is to hardcode links between switches so that there is no question on how it negotiated the link . Rule of thumb Switch #1 10 or 100/full---------Switch#2 10 or 100/full or Switch1 AUTO-------Switch#2 AUTO

New Member

Re: CDP errors with mixing full/half duplex links on switch

BTW--- The switches that are complaining via CDP, are not networked via the same link. (i.e. one end of the link set incorrectly) Switch A, is complaining about switch B, which is on another LAN segment altogether! Why should switch B, on another segment, care about the link settings of switch A?

Thanks thus far. :-)

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