iMac intermittent LAN ethernet connectivity problems

I have a problem with the ethernet LAN connection on my iMac. Connecting to areas on the network, webpages is very intermittant with sometimes no response at all. I am in an enviroment where it needs to be cable connected to the network. It was originally on OSX 10.8 but have since upgraded to 10.9 and no change.

As a test I have set up a continuous ping to a server on the network and to google in terminal. Every few hits the ping fails to get a response. There is no pattern, completely random.

Doing the same test over WiFi and the terminal ping doesnt miss a beat. So definately looks to be a wired problem.

I have tried a PRAM reset and completely re-installing the OS which has not helped.

Does anyone have a suggestion what I can try?

Thanks

Thanks for your response. Yes sorry forgot to mention that one, I have tried different cable and what sockets its plugged in to.

Thanks

Everything is dynamic DHCP on the network. Using a static address does not improve anything. Just to confirm, there is no conflicting address either.

Using another iMac in the same physical connection doing exactly the same pings works without fault. No missed pings/request time outs.

There are 2 hops before the outside world, but as I mentioned earlier it suffers the same results pinging an internal server which happens to be connected to the same switch.

Its a big network but only having problems with this one unhappy iMac.

Thanks again.

No config errors. Almost definitely a hardware fault.

Problem solved with this adapter:
http://store.apple.com/uk/product/MC704ZM/A/apple-usb-ethernet-adapter?fnode=51

This is a 2009 21". Yes this was very intermittent when internet browsing or using network shares. Just simply pinging another network device proved there was an issue.

On this model, the ethernet connection is physically part of the back of the logic board soldered on, so I was unable to try that as a first port of call. I have seen on the some of the later iMacs that this is a separate replaceable board, which is what I was hoping for.