Cisco 4500 - No duplex command?

I have a Cisco 4500 router in an office. I received a warning from my Aironet device that the duplex set on the Cisco 4500 was set to half. (Duplex mismatch) I checked the interface and it says it is in half-duplexing mode. (Show Interface Ethernet 0 displayed this. Show Run did not display the duplexing information.) I wanted to change the Cisco 4500 to Full-Duplex on Ethernet 1. However when I go to the interface, the duplex command is unavailable. (The Cisco 4500 is connected to a switch) The IOS is Ver. 12.0(7).

Any ideas why I cannot change the duplexing mode?

(I'll have to check out what ethernet module is installed into the device. I am currently off site, so I cannot tell you yet)
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I don't believe the old 4500 router supports full-duplex at all unless you have the NP-2E-FDX module. Even then it is only 10Mb


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lrmoore is correct. Best to set the AP to half or "auto."
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