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Community Member

Duplex issue

I cannot seem to correct a duplex mismatch issue.

I have a Cisco 2950 switch connected to a Cisco 2621 router.  I am running a per-interface Vlan.  I have two fastethernet ports and one NM-1E card installed on the router.  One fastethernet port is connected to my gateway router, the second fastethernet port is connected to my switch for one Vlan.

The NM-1E Ethernet card is being used for the second Vlan which consists of nine IP cameras. 

Though the cameras on the Vlan are working fine, I am having major collision problems with the message being:

%AMDP2_FE-6-EXCESSCOLL: Ethernet1/0 TDR=0, TRC=0.

Now, the NM-1E card is set to half-duplex.  I know that I should be using a fastethernet module like a 1FE 2W or a 2FE 2W card, (which I have,) but the router does not recogonize either one of these cards when they are installed, and yes, they have been confirmed as good cards.

Using Router-on-a-Stick configuration is out due to the bandwidth contention besides the fact that the router I am using it on will not handle this due to the flash being an older version.

Here is what I have done thus far to try to correct the collision issue:

  1. I have forced the switchport to half duplex, setting the speed to 10.  This did not fully resolve the issue, but helped some.  I was getting fewer error messages at first, but they soon increased back to the frequency that they began with.
  2. I have set the switchport to duplex auto, but this failed to resolve the issue.
  3. Obviously, I cannot force the switchport into duplex full since the NM-1E interface is set to half duplex.

I am open for suggestions at this point and have two addtional questions.

  1. Can the NM-1E card be configured to full duplex?  I can't seem to find any documentation showing where it can be forced to full duplex mode.
  2. Could nine IP cameras just be too much for both the router and switch to handle?  I wouldn't think so, but ...

Again, I am open for suggestions at this point.


Hall of Fame Super Silver

Duplex issue

Hello Steve,

if you cannot configure duplex full under eth1/0 on the router the port is only half duplex


interface eth1/0

duplex full

command accepted by the router ? 


Could nine IP cameras just be too much for both the router and switch to handle? 

this is the point a 10 Mbps half duplex can perform at max 3.3 Mbps in theory even less in reality. It cannot run at 10 Mbps.

Even with low resolution ( = low bit rates) nine cameras easily overcome this figure.

The best move would be IOS upgrade in order to be able to:

- support vlan subinterfaces on FE port

- and to mount an FE additional module like one of those you have and that are not recognized at the moment

Hope to help


Community Member

Duplex issue

Strange thing has occurred.  I attempted to change the Ethernet port to full duplex and this time it took the command.  I don't know why it didn't previously, and everything I read pointed to not being able to do this even though there was no confirmed NO to this configuration.

Once done, I forced the switchport into full duplex at the speed of 10 and now everything is GTG; all of the excessive collision messages have gone away as well.



Re: Duplex issue

  If you cant change the interface from half duplex you have to live with collisions as this is part of a half duplex connection and is working as designed.  Know that as the utilization goes up on half duplex link it will get slower and slower.  Anything above 30-35% utilization on a half duplex link will make it real slow. You can't work miracles on very outdated technology . 

Community Member

Duplex issue


As stated above, I attempted to change the duplex to full and this time the router took the command.  Thanks for your help here as well.

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