UK- Virgin Media Network Issue

copied from a post i made on the vm forums

Although by no means would I call myself an expert in networking I have enough knowledge to get by. Anyways over the last few days I have come across a problem for which although I have figured out the solution, I dont understand why it works and I was hoping I might get some insight here.

So onto the problem. With the modem connected directly to the PC everything is fine. However as soon as I try to add in a router, the router gets stuck on connecting. In the status page it shows up as aquiring a ip address and gets no futher. This shows up out of the blue with no real explaination. So I spent a good couple of hours checking, double checking etc all the usual suspects. ie router settings, internet settings, wiring etc. Through pure luck I found the solution which was to swap the ends of the RJ45 cable that connects the modem to the router.

I had this confirmed when a friend had an identical issue (with a totally different brand of router (however both were Wireless-N routers) I again tried all sorts of checks with nothing working until I again swapped the ends of the cable. Straight away everything was fine again.

So I have the solution, what I dont have is an explaination as to what has gone wrong or why this actually works. Any insight would be helpful.