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My ISP has provided a crappy Thomson cable modem with 4 LAN ports and wifi, which constantly crashes and reboots itself. I am going to ask for a replacement, but here is my question:
--> I have a WRT54G that I don't currently use -- can I just use that instead?

I suspect that I can't use it, because the WRT54G has 4 LAN ports and an Internet port which is also RJ-11, not RJ-45 that matches my phone line (the current cable modem connects directly to the phone socket in the wall, I have no wired phone or anything else on that "phone" line).

On the other hand, the WRT54G has settings for PPPoE and several other login types, so this makes we think that maybe it can work as cable modem after all...?

If I can't replace the cable modem, I would still like to add the WRT54G so that everything connects to that instead. For this, I would need to set up the cable modem to not do all the DHCP and port stuff, and set up the WRT54G to do all that instead. This question pretty much describes what I want, but provides little information. I will have to dig into the cable modem manual to see if it's even capable of that trick.
--> Is this recommended? I'm "good with computers", but not a network admin...

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If the modems that the cable company are sending you are junk, you could purchase a quality dedicated modem or combo modem/switch/router. Just get something good.

As far as connecting your WRT54G to your current cable modem, you'll connect the cable to the modem's input, and you'll connect the modem's output port (RJ-45) to the WRT54G's input (WAN side). The output ports of your WRT54G will now be your LAN.

The thing you'll need to be aware of is that if the provided cable modem is junk, it will still be junk after adding the WRT54G, so your situation may or may not improve. If that's the case, get a better modem.

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Any recommendations for a better modem? I was under the (false!) impression that the WRT54G did include the modem functionality. I like the GUI of Linksys products, but it's not a must. – Torben Gundtofte-Bruun Aug 21 '10 at 6:24
Sorry, I'm on DSL, so i can't recommend one. But look at the datasheet for this Motorola SB6120 modem. The back panel shows the cable input connector, and the RJ45 output connector. If you connect onle your PC to this output, your sitting directly on the internet. Connect your WRT54G here, and the router is between you & inet. Any other dedicated modem will be similar, and any router that accepts cable will have the cable connector. Here's the link:… (cont...) – Joe Internet Aug 21 '10 at 13:33
(cont...) There are several modem manufacturers. See the "cable modem wiki" for a list. Also, the reason for the PPPoE and similar is so that your router can authenticate to the modem, taking the place of the connection software your PC would use if it was connected directly to the cable modem. Lastly, if your WRT54G is older, update to the latest firmware, or run third party firmware such as dd-wrt or tomato. Both offer upgraded features over stock firmware, but just be able to revert back in the event of a problem. – Joe Internet Aug 21 '10 at 13:38
up vote 0 down vote accepted

This answer may be just right, but I'm not sure. Comments?

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My cable modem doesn't feature anything like a "bridging" mode, and it doesn't look like I can disable DHCP either. Doesn't look too promising :-( – Torben Gundtofte-Bruun Aug 21 '10 at 6:05
I just found that disabling the modem's DHCP is possible after all! So I can't replace the modem but I can offload most of the "work" to the router. Perhaps that will be enough to keep the modem from rebooting - which is my only goal. – Torben Gundtofte-Bruun Aug 21 '10 at 6:28
The answer linked above is just what I need. (Turns out I have a DSL modem, not cable modem as I originally wrote. My mistake.) – Torben Gundtofte-Bruun Aug 23 '10 at 12:26

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