are all cable modems external?

Your modem has a config file that tells it how many computers can be connected to it. If you simply change cables without power-cycling the modem, and it is configured to only allow one connection, then if the USB port was the first one connected, then that's the only one that will work.

Some modems, like Motorolas, will allow both the USB and Ethernet ports to be used at once if the config file allows two or more connections. Other modems, like RCA's, do not allow both interfaces to be used at once. So even if you're paying for more than one IP address, you may not be able to use both interfaces at the same time.

Some RCA modems even resist switching between the two interfaces even after cold resets. So even if you're only connecting one device at a time, and you're doing a full, cold reset of the modem, you'll have difficulty switching between interfaces.

There also could be a problem if the USB and the Ethernet network connections have been bridged by the OS. The Ethernet card may have worked just fine when it was the only network interface, but once you started using the USB interface for networking, you may have caused a problem.

Borrowing someone else's modem won't help you troubleshoot. The modem you use needs to be provisioned for your account. If it's provisioned for their account, and you're on the same network segment, it might work at your house. But if it's provisioned on a different network segment, connecting it at your house won't work. It may mess-up your friend's account as well.

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Okay, I don't quite understand all of the technical, but I get the

overall idea that I should just plan on buying an external modem and an

external router w/built in firewall. Thanks for the help! I considered

going with the Motorola wireless, which seemed to combine all, but am

concerned that wireless may contradict the security of a firewall that

I am trying to achieve.

Unrelated networking/modem question - (I'm getting bounced back and

forth between Comcast and the person who built my computer as to where

the problem is on this issue.) I can connect to the internet via my

USB port, but not my LAN/ethernet port. When checking ipconfig, the

USB connection returns a valid ISP address, but the ethernet connection

returns an invalid 169... address. Comcast says it's either the

ethernet card or the ethernet cable. My friend who built the box (in

another state and VERY BUSY) says that the ethernet card is fine, since

he used it to set things up, and we downloaded all of the most

up-to-date system drivers from the Shuttle website, so it must be a

problem with Comcast. I bought a new cable to replace the rental one,

but no change. My next attempt might be to borrow a friend's modem, or

go ahead and buy the one I want to keep, and replace the rental modem to

see if there's a problem with the connection there. Any


Warren Wrote:

Jen wrote:- > I'm new to cable internet access and am researching Modems. From > these > discussions, the Motorola SURFboard 5100 modem seems pretty hot, and > Linksys seems to be good for its routers. I'm trying to keep my > total > footprint very small (cute little Shuttle XPC), and wondered if there > even was such a thing as an internal cable modem, just as there is > for > dial-up access. > > Also, I need firewall hardware, not just the firewall software. Do I > need to buy a modem and router (only one PC needs access at a time) > and > a firewall all separately, or are any of these manufactured in a > combined product?- > > There are some internal cablemodems, but they aren't on most cable > companies' lists of acceptable modems. They may be DOCSIS compliant, > but > that's only the first level of compatibility. The cable company has to > be > willing to support the modem with config files, and firmware updates. > An > internal cablemodem also has the disadvantages that it cannot be > separately > reset, and would also require OS-specific drivers. So even if the > stars > align, and your cable company allows any of the internal modems > available, > you'd be paying a high price just for cosmetic purposes. > > Most OS's can also act as routers. Windows has Internet Connection > Sharing, > for example. With multiple NIC's, and the right software, it can be > done -- > just not well. The computer's primary purpose is to run applications, > and > while pre-emptive multitasking is a wonderful thing, it's not a great > environment to be running network routing services at the same time. > And if > you have an undersized case, there probably isn't room for multiple > NIC's. > > The simple, consumer-level "broadband" router combines basic router > capabilities, and provides a basic firewall as a side effect of using > NAT. > NAT means that each computer on your LAN has an internal IP address, > and the > only IP address that faces the rest of the world is the single, shared > address of the router. Thus incoming packets need to be expected so > they can > be translated to the right internal node. A true firewall goes far > beyond > NAT, and would be a separate box. However, based on the questions > you're > asking, you are highly unlikely to be in a category that requires more > firewall protection than a NAT router can provide. > > There are cablemodem / router combinations, however they also have > deficiencies that far outweigh any cosmetic reasons for wanting them in > a > single device. > > If aesthetics are so important that you just can't have these boxes > near > your desk, Cat5 Ethernet cable can be up to 100 meters long, so you > can > always place your cablemodem and router in another room, and have > nothing > but the cable coming out of the wall. > > -- > Warren H. > > ========== > Disclaimer: My views reflect those of myself, and not my > employer, my friends, nor (as she often tells me) my wife. > Any resemblance to the views of anybody living or dead is > coincidental. No animals were hurt in the writing of this > response -- unless you count my dog who desperately wants > to go outside now. > Care for your landscape with Black and Decker cordless tools >
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Warren wrote: ....

Provisioning is probably the most "new" thing to DIY folks who think a cable modem is just like a 56kbaud modem, only for 'cable', but actually it is Very Different. Warren makes an excellent point that you (the OP) should understand.

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