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DSL modems are typically provided by your ISP. Most people don't realize that you can often purchase your own ... but should you?

What opinion do you have about buying a modem instead of using one supplied by the ISP. Presently I use a dsl modem supplied by my phone co. which is also my ISP. Somewhere in my web rambling I read that modems seem to invite spies, malware and viruses. I don't know how but that's what i think the writer said. As I've been perusing today's newsletter I also see that you mention that it's feasible for people to see our internet addresses if two PC's are behind the same router,which mine are. Do you have any feelings or fears about such things? One thing I don't like about my modem is that the default address of the modem must always remain the same. I am thinking that perhaps with a different modem I could have some leeway in changing the address from time to time as I do with my router.

There's a fair amount of confusion evident in the question, because the modem isn't really related to many of the things mentioned. That's fine, and I'll do my best to clear that up.

Purchasing a modem, rather than using the ISP provided one, isn't all that common but can occasionally be useful. In fact, I had at least one case where I actually had to buy my own. On eBay, no less.

A modem - short for modulator/demodulator - is simply a device that converts one type of electrical signal to another. Originally, it was specifically used for dialup where electrical signals used to connect to your computer were converted, or "modulated", into sounds or audio signals that could go over regular telephone lines. The reverse, listening for incoming audio signals and "demodulating" or converting them to the electrical signals used by the attached computer was the other half of the job.

"There's nothing about a modem that might 'invite spies, malware and viruses'."

Very, very technically they're not modulating and demodulating quite the same way any more, but the concept still applies. These days your modem probably takes one type of signal as input - an Ethernet connection - and acts as a converter between that and the DSL signal that travels on your phone line.

But that's really all a modem is - a glorified signal converter that's just a part of getting your computer physically connected to your ISP.

There's nothing about a modem that might "invite spies, malware and viruses". It's hard to even explain why, other than to say that the very concept doesn't apply. I suppose just connecting to the internet is a kind of invitation, but the modem neither helps nor hinders malware any more than valid internet traffic. It's just a conduit.

Similarly, when you connect to your ISP, you are assigned an IP address. That IP address is either assigned to one computer, if you're not using a router, or to the router if you are. All the computers you might have connected to that router have local IP addresses that are not visible on the internet. When any of those computers access the internet they all look like they're at the same internet IP address assigned by your ISP.

Your modem didn't play a role in that. Again, it's just a conduit getting your computer or router connected to your ISP.

Changing your modem - or your router for that matter - will probably not have any affect on your IP address. Certainly powering off your modem might cause the next IP address you're assigned to be different - or not. It all depends on how your ISP assigns and re-uses IP addresses.

Having the same IP address for a lengthy period of time shouldn't make you uncomfortable, either. Most people have them for months, or, in my case, years since I've specifically been assigned an unchanging or "static" IP address. Without a court order your IP address actually tells very little about you. (And with a court order it probably wouldn't matter if your IP was changing frequently.)

Now, there is one potential point of confusion: so far I've talked about modems and routers being separate devices, and usually they are.

But sometimes they're not.

Occasionally some models will also include the functionality of a router.

Nothing in my discussion above changes: it's not inviting malware, and it has no additional impact on how often your internet IP address changes. It just means you don't need an additional router.

So, what about buying your own?

In short, I wouldn't unless there was a reason you needed to.

By using your ISP's modem you're getting their support, and a guarantee that if something changes they'll be responsible to replace the modem as needed. And yes, things do change - not all DSL is the same, and if you do purchase a modem of your own you'll need to make sure it's compatible with your ISP's system.

In my case, my ISP was transitioning its technology, and when my modem failed they no longer had replacements for it. I was on some old DSL technology, but they couldn't provide me a modem to be used with it. (What's worse is that technically with the new technology I was also no longer eligible for service being slightly too far away, so they couldn't just upgrade me.)

That's why I landed on eBay, desperately searching for a replacement modem. (Which I found.)

That's also in part why they're no longer my ISP.

Article C4278 - April 23, 2010 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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9 Comments
Mike
April 23, 2010 11:36 AM

Interesting topic! I've had the same question as to whether or not to purchase my own (cable) modem. I found a sufficient one for less than $60, while my ISP charges $5 per month to rent it. So I would make my money back in less than a year.

The only thing that stopped me from doing it is that one of my troubleshooting steps when I'm having a problem connecting to the Internet is to swap out my cable modem with another one. If I purchased my own, doing this would mean I would have to buy another one. However, by renting, I'm able to go to my ISP and just swap my current one for another one, no additional cost.

Michael Horowitz
April 26, 2010 9:15 AM

I know someone with two residences, they spend roughly half the year at each location. They started out at one location with a modem provided by the cable TV company but eventually purchased their own modem. When they left for the season and turn off the Internet, the cable company wanted their modem back. Hooking up the modem and unhooking it, plus picking up and returning the modem, were a big hassle. Now that they own their own modem, Internet service can be turned off/on remotely. No more need to ever touch a coaxial or Ethernet cable.

On a side note, modems and routers are computers, thus, like computers, they too, should be surge protected. I connect mine to a UPS, in an attempt to avoid outages of any type. But, that's me.

Richard J.
April 27, 2010 12:49 PM

Posting for Mike at April 23, 2010.

Are you sure you are not talking about swapping out routers for troubleshooting. Modems have MAC addresses that require your ISP to change if you swap out modems. If you are going to your ISP to swap out the modem they will do the change there, but my question is why?

To find out if your modem is bad all you have to do is call your ISP and ask them to look for your modem. They will "Ping" it and if it replies, your modem if fine. Simple and saves gas.

Richard
April 27, 2010 2:45 PM

I travel for extended periods of time so I own my modem. That way I can suspend my internet service while not having to arrange for my provider to pick up the modem, which I would have to do if they owned it and I suspended service. All it takes is a phone call to my provider to suspend or restore service.

Lynn Hancock
April 27, 2010 5:05 PM

Here in Australia, combined modem/routers seem to be a lot more common than separate devices. My ISP does not rent out modems/routers, you have to buy your own. You can buy any standard unit, but the ISP can sell you their preferred model. I chose the latter as they fully support it, pre-configured it for my installation and made it available at a substantial discount (depending on the length of the initial contract I was prepared to sign up to - as I had already spent two years with them on dial-up and was quite happy with their service and support, I had no hesitation in signing up for an initial 24-month period to get the maximum discount, which I have not regretted). It is a four-port Ethernet/wireless modem/router made by Belkin specifically for this ISP.

Of course if the modem/router ever fails, I will have to buy a new one, but as it has worked flawlessly for over four years now, I feel it owes me nothing.

Mark
April 29, 2010 6:19 AM

One of the dirty little secrets of broadband (in my area at least) is that if you use the ISP's modem, they "give" you the first one, but if it fails for some reason, you have to purchase it's replacement, which, in the case of DSL, is proprietary. Also, any of the modem/router combination units utilized when you purchase bundled voip with broadband & cable are also proprietary. Cable modems that only provide internet service can still be replaced using readily available units both online and retail. Lastly, the ISP's opinion of "your modem is working" doesn't necessarily mean "it's working at 100% efficency. Learn how to get to your modem's internal logs and how to read them, then you can judge for yourself if you're getting all the service you are paying for. If not, replace the modem, even if it means paying for it yourself.

Mike
May 10, 2010 10:53 AM

REPLY TO: Richard J. at April 27, 2010 12:49 PM

No, I am talking about my cable modem. No waste of gas, as I drive by my ISP on my way to work every day. And other than calling my ISP to ask if they are having an outage, I refuse to ask for their troubleshooting assistance, as they always end up saying they want to send out a tech for $100 per hour. No thanks!

Miguel Pode
April 8, 2011 9:35 PM


Greetings.

I´d been a field "technician" for a while, and I got a very disturbing question about this article:
How about to connect 2 pc's remote pc's using 2 ADSL modems and a very inexpensive long telephone cable? I know that line isn´t a propper phone line with hardware and signals implied in it, but, it may work, isn´t? After all, ADSL modems uses THE WIRE, not DCV or ACV and currents normally supplied by a Phone CO.....
And I fairly know that CO modem is configured as A.T.U.-C (ATU -> Adsl Termination Unit - Central office) and remote user one as A.T.U.-R (idem - Remote)
Can ATU-C mode be settled up?
Thanks!

Roy Weber
April 3, 2012 5:27 PM

Just found out I have been paying $7.00 a month for years renting my modem from comcast. I could have bought several with what they recieved from me. Just ordered one on E Bay.

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