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Reply To: I am having some severe trouble with my PCWRT dual band router

#3470

bjensen2
Participant

Arris supplies the majority of modems used on cable internet service in the USA. There are millions and millions of them deployed. A systematic problem with Arris modems seems highly unlikely. What’s described in that post sounds like something Spectrum has imposed on their subscribers. An ISP can modify the behavior of the modem pretty much at will. But I’m not on Spectrum, and I’ve had no issue with several devices connecting to the T25, including my PC and a couple of different routers. This problem only arises with the PCWRT. I have a more plausible idea about what I’m seeing.

The issue I’m encountering will manifest if there are multiple devices with the same MAC address on the network. One thing that makes me suspect this might be the case with the PCWRT is that the burned-in address doesn’t match the sticker on the bottom of the router (it lists XX:XX:XX:XX:XX:0C). Another thing is that the first WRT router, which was manufactured at least three months prior, if not earlier, had a very similar MAC address. The difference between the old and new MAC addresses is only 36 in decimal. Presumably more than 36 routers were manufactured during those months. So the MAC addresses of these routers are not sequentially incremented, and if they were randomly distributed across the 16 million possibilities available, the odds of me receiving two routers with random addresses <= 36 bits apart are phenomenally long. So my hunch is that many PCWRT routers ship with the same MAC addresses – hundreds or maybe even thousands. In fact, the reuse of MAC addresses is pervasive enough that I’ve now had two of them that were not unique on the particular segment of Comcast’s network to which I am connecting. That is, some other frustrated Comcast/PCWRT customer was experiencing the same problems that I was. There’s a way to test this theory… and I did.

I tried the “random MAC address” option in the internet settings. This seemed to work just as well as the cloned address (and I actually do think the cloned address took effect, it is just a bug in the UI that does not display it on the status page). The reason that a random address would work is pretty simple – the randomly selected address is one of the 16 million possibilities that doesn’t match any used on any PCWRT routers manufactured to date, or at least not any that have been put into service on my network segment.

I don’t really want to go forward with a cloned MAC address as that could later lead to a problem if the gigabit router is put back into service. I think the randomized MAC address is a reasonable fix, although I’ve never needed to do this with any other piece of networking equipment.

If you do not believe that duplicated MAC addresses are the source of my issue, please explain why the randomized MAC address option (which, by the way, does seem to display correctly on the status page) would resolve the problem.