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I have a Belkin router, and about a year ago, I suddenly lost my internet connectivity from Comcast. The internet worked fine when I plugged it right into my laptop, so I just ignored it. When I moved to another apartmnet I eventually took the dive and called tech support. The tech told me to clone my MAC address which completely fixed the issue.

Now I know what a MAC address is and I've read what MAC cloning is. What has bothered me since is that I don't see how this fixed the issue. As I have understood MAC address cloning, it has the router pretend it has the same MAC address as my computer. Here is why I don't understand why this fixes my issue:

  1. I have used several different computers with this router. Cloning the MAC address fixed it for ALL of my computers. The laptop I first used with my ISP was not the one that I eventually had connected when I cloned the address. Furthermore, I didn't have any problems for quite some time after I stopped using the first computer. It wasn't like the internet suddenly stopped working when I changed which laptop I was using Now it occurred to me that maybe there was some sort of expiration? Except...

  2. Which MAC address did it clone? It was just an option in the router administration page. Did it just pick whichever computer was connected to it? If my ISP still wanted the MAC of my first computer, how did some other computer's fix it?

  3. As mentioned earlier, why did this problem seemingly stem from nowhere?

Anyway, I don't have any current problems so this is more just out of general curiosity. If anybody can explain it, it would be appreciated!

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2 Answers

up vote 2 down vote accepted

MAC address cloning is used because some ISP don't want you to have a router connected to the modem. What usually happens is that when you connect a computer to the modem, your ISP gets your NIC's MAC address and is able to recognize when you connect a router to the modem.

When you clone the MAC address it clones which ever computer you used to connect to your router, you can verify that by going to your command prompt and running "ipconfig /all" you'll see your MAC address there, if you go back to your router's admin panel and compare MAC addresses you'll see that they're the same.

Some ISPs are able to figure out if you're using a router by the vendor code and disconnect you. If they see the MAC as just a NIC, they've got no reason to drop your connection.

From my understanding Comcast assigns their customers an IP based on not the cable modem's MAC address, but the MAC address of the device next in line within a network. Whenever you connect a device to the modem it's important that you perform a power cycle.

As to why the problem stemmed from nowhere, your guess is as good as mine. Could be because of something Comcast did.

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This isn't a great answer but I guess I'm not getting a better one - it sort of restates what I already knew without any clarification. I thought the MAC address of my computer and router would match, and at first I thought they didn't, but now I realized it matches my wired connection but not the wirelesss connection (which makes sense). What still doesn't make sense is why cloning the address of a different computer would help. –  MetricSystem Apr 17 '10 at 21:31
    
Well like I mentioned before it doesn't really matter what MAC address gets cloned as long as it isn't a router address. The first 3 codes of a MAC address identify the manufacturer of the card and the remaining codes are used to create a unique number. Your ISP is able to find out from the vendor id whether or not you have a router connected. Try this, coffer.com/mac_find it will tell you your vendor based on your MAC.So to reiterate it doesn't matter if the cloned address isn't from the first computer that was connected to the modem. My apologies if my explanation wasn't clear –  Serge Apr 18 '10 at 14:34
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What you're cloning is the mac address of the computer you had when you signed up with your isp. Therefore every device you now connect to your router shows up to the isp as that original computer. Therefore it does matter what mac address is cloned

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