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Duplex mismatch - Switch changes port speed

Posted on 2005-04-22
Medium Priority
Last Modified: 2008-03-04
I have a Cisco 2950 switch.  I have a port duplex mismatch between a port on the switch and a server.  The NIC in the
server is an Intel Pro/1000 CT Gigabyte card.  It has the latest drivers dated 11/22/04.   The port on the switch
is set to 100/Full.  This NIC doesn't like that setting and will only run, if I set both the port and NIC to auto.

When I set the port on the switch to Auto, it will run for a couple of days, but eventually will set itself back
to 100/full.  Has anyone ever heard of this?  

Thank  you
Question by:keicy01
  • 2
LVL 79

Expert Comment

ID: 13845401
Here's the thing ...
If you set the server NIC to 100/full, then you have to set the switchport to 100/full
If you leave the server NIC at auto, then the switchport must be on auto
If you set the switchport to 100/full, then you must set the server to 100/full

If it works at auto/auto, then what is the issue?


Author Comment

ID: 13850091
It works at auto/auto but the switch port changes back to 100/full leaving the NIC at auto which causes the mismatch.
I found a small blurb about some switches not able to negotiate link speed with the Intel Pro/1000 CT card.  I swapped out the card and that seemed to work.
LVL 79

Accepted Solution

lrmoore earned 375 total points
ID: 13858911
If you're looking at the switchport using "show interface" it will show whatever speed/duplex it has negotiated.
If you look at the config with "show config" and you should not see the speed/duplex settings. If you see them in the config as below, then I would be concerned because a Cisco device can't automagically configure itself..

  interface fast 0/4
   speed 100


FastEthernet0/2 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 000e.842b.ea82 (bia 000e.842b.ea82)
  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, media type is 100BaseTX  <=== "negotiated speed/duplex"

There is no speed/duplex setting in the configuration from 'show config'

interface FastEthernet0/2
 switchport mode access
 switchport port-security
 switchport port-security aging time 2
 switchport port-security violation restrict
 switchport port-security aging type inactivity
 macro description cisco-desktop
 spanning-tree portfast
 spanning-tree bpduguard enable

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