Running Linux, 5th Edition - Matthias Kalle Dalheimer [264]
Finally, we should mention that a small number of weirdo ADSL modems are not connected with an Ethernet cable , but rather with a USB cable. This is technically a bad idea, so you should avoid these modems if possible, but if you are stuck with one, you can find more information, including drivers for some devices that run PPPoE on a USB connection (that would be PPP over Ethernet over USB, then!), at http://eciadsl.flashtux.org and http://speedtouch.sourceforge.net.
Whichever way you use ADSL (with or without an ADSL router), you need to set up the correct IP address. This can either be static (in which case you should find it in the information you have received from your ISP) or dynamic and assigned via DHCP (Dynamic Host Communication Protocol), in which case you can request a dynamic IP address with the following command:
dhclient eth0
Of course, if the Ethernet card you use has another name, you need to replace the eth0 with the correct name. Instead of dhclient, you can also use the utility pump. There is also a DHCP daemon called dhcpcd that runs in the background and assigns a dynamic IP address whenever necessary.
Finally, many ISPs require that you activate your line from time to time. How you do this depends on your ISP, but often the activation requires nothing more than browsing to a certain web site and entering the credentials there that your ISP has assigned to you. As mentioned before, you may have to repeat this step from time to time.
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[*] The reason why the providers do this is that they want to prevent you from running a server, coercing you into upgrading to a more expensive "business" subscription if you wish to do that.
Cable Modems
When one wants Internet access enough, any wire will do. There are intensive experiments to use even the electricity grid to deliver Internet access. So it's not surprising that companies that built their business plans on delivering laser-crisp pictures of sporting events (the cable TV firms) would realize they could devote one of their channels to a local area network carrying digital data—hence the advent of cable Internet access.
The bandwidth on the cable infrastucture theoretically ranges up to 10 Mb (like an old Ethernet on coaxial cable), but some providers today achieve more throughput. Usually, they span a web of nodes, each of which offers 10 Mb or less. The neighbors who share the node have to share the bandwidth. So if there are two users on the node, each gets 5 Mb. Furthermore, some customers near the center (the central server, which is usually connected via the optical fiber cable to the rest of the Internet) have more bandwidth than those at the periphery. So check your cable network very carefully before you sign up for Internet access. Talk to the technical support first, and if they cannot answer your question, this might be a good indication about how good their support is going to be later.
ISPs that sell clients Internet access through cable modems will usually take responsibility for service all the way to your Ethernet card. They will give you a cable modem with a coaxial cable connected to their cable infrastructure, and an Ethernet (RJ45) connector on your side. To set up your Internet connection, you will need to know the IP address assigned to the cable modem, the network mask, and the gateway; your ISP should provide you with this information together with the cable modem. On your side, you need only start up your (carefully configured) Ethernet card with the data provided to you by your ISP:
/sbin/ifconfig eth0 IP_address netmask
Next, tell the kernel about the gateway:
/sbin/route