over copper telephone lines from a central office to individual subscriber sites
(such as your home). Many DSL services (technically, cable rather than DSL)
provide asymmetric speeds with download speeds greater than upload speeds.
NOTE
DSL service is an “always-on” type of Internet service, although you can
turn off the connection under Ubuntu by using the network configuration
tool found under System, Administration, Network. An always-on
connection exposes your computer to malicious abuse from crackers who
trawl the Internet attempting to gain access to other computer systems. In
addition to providing the capability to turn off such connections, Ubuntu is
preconfigured to not listen on any network ports, which means that any
attempts to gain access to your computer fail because Ubuntu rejects the
requests. This is the Ubuntu equivalent to surrounding your computer with
a 12-foot steel fence.A DSL connection requires that you have an Ethernet NIC (sometimes a USB
interface that is not easily supported in Linux) in your computer or notebook.
Many users also configure a gateway, firewall, or other computer with at least
two NICs to share a connection with a LAN. We looked at the hardware and
protocol issues earlier in this chapter. Advanced configuration of a firewall or
router, other than what was addressed during your initial installation of
Ubuntu, is beyond the scope of this book.
Understanding PPP over Ethernet
Establishing a DSL connection with an ISP providing a static IP address is
easy. Unfortunately, many DSL providers use a type of PPP called Point-to-
Point Protocol over Ethernet (PPPoE) that provides dynamic IP address
assignment and authentication by encapsulating PPP information inside
Ethernet frames. Roaring Penguin’s rp-pppoe clients are available from the
Roaring Penguin site (https://www.roaringpenguin.com/files/download/rp-
pppoe-3.11.tar.gz), and these clients make the difficult-to-configure PPPoE
connection much easier to deal with. You can download and install newer
versions.
NOTE
When ISPs originally started to roll out ADSL services, they often provided
the ADSL modems. Today, however, in much of the world these modems
are optional, which is a good thing because many people choose to
purchase a router with a built-in modem to create a dedicated connection. In
the United States, ADSL modems are rare, but you can usually replace the