The truly frugal can also "network" two Linux workstations using a null-modem or LPT cable and PPP, as shown in the PPP HOWTO at http://tldp.org/HOWTO/PPPHOWTO/direct.html . Just connect two PCs running Linux together with a null-modem cable, and use the pppd daemon on each end. If one Linux host is connected to a network or has a dial-up connection, that PC becomes a gateway for the other host. You have to use pppd 's defauitroute option on the serial-only host when connecting.
Each NIC has a unique address (the hardware address, known as media access control , or MAC), which identifies that NIC. This address is six pairs of hexadecimal bits separated by colons (: ). A MAC address looks similar to this: 00:60:08:8F:5A:D9. The hardware address is used by DHCP (see "Dynamic Host Configuration Protocol " later in this chapter) to identify a specific host. It is also used by the Address Resolution Protocol (ARP) and Reverse Address Resolution Protocol (RARP) to map hosts to IP addresses.
This section covers some of the different types of NIC used to connect to your network. Token Ring
Token ring networking was developed by IBM. As the name implies, the network is set up in a ring. A single "token" is passed from host to host, indicating the receiving host's permission to transmit data.
Token ring has a maximum transfer rate of 16Mbps (16 million bits per second). Unlike 10BASE-2 and 10BASE-5, token ring uses what is called unshielded twisted pair (UTP) cable. This cable looks a lot like the cable that connects your phone to the wall. Almost all token ring NICs are recognized by Linux.
10BASE-T was the standard for a long time. A large number of networks still use it. 10BASE-T also uses UTP cable. Instead of being configured in a ring, 10BASE-T mostly uses a star architecture. In this architecture, the hosts all connect to a central location (usually a hub, which you learn about later in the section titled "Hubs and Switches "). All the data is sent to all hosts, but only the destination host takes action on individual packets. 10BASE-T has a transfer rate of 10Mbps.
10BASE-T has a maximum segment length of 100 meters. There are many manufacturers of 10BASE-T NICs, and most are recognized by Ubuntu.
100BASE-T waspopular around the turn of the millennium, keeping the same ease of administration as 10BASE-T while increasing the speed by a factor of 10. For most networks, the step from 10BASE-T to 100BASE-T is as simple as replacing NICs and hubs. Most 100BASE-T NICs and hubs can also handle 10BASE-T and can automatically detect which is in use. This allows for a gradual network upgrade and usually does not require rewiring your whole network. Nearly every known 100BASE-T NIC and most generic NICs are compatible with Linux, thanks to Donald Becker of http://www.scyld.com/ . 100BASET requires category 5 unshielded twisted pair cabling.
1000BASE-Tusually referred to as gigabit ethernet is the accepted standard in enterprise networking, with most NICs being detected and configured correctly by Ubuntu. Like 100BASE-T NICs, gigabit NICs automatically downgrade if they are plugged in to a slower network. Also like 100BASE-T, gigabit NICs require category 5 unshielded twisted pair cabling; however, many institutions are now deploying category 6 cables because they have much longer range and so are often worth the extra cost. You will find that many newer computers tend to be fitted with gigabit NICs as standard.
Fiber Optic and Gigabit Ethernet
Fiber optic is more commonly used in newer and high-end installations because the cost of upgrading can be prohibitive for older sites.
Fiber optics were originally used on fiber distributed data interface (FDDI) networks, similar to token ring in structure except that there are two ringsone is primary, whereas the other is secondary. The primary ring is used exclusively, and the secondary sits idle until there is a break in the primary ring. At this point, the secondary ring takes over, keeping the network alive. FDDI has a speed of 100Mbps and has a maximum ring length of 62 miles. FDDI uses several tokens at the same time that, along with the faster speed of fiber optics, account for the drastic increase in network speed.
As stated, switching to a fiber optic network can be very costly. To make the upgrade, the whole network has to be rewired (as much as U.S. $150 per network connection), and all NICs must be replaced at the same time. Most FDDI NICs are recognized by Linux.
Fiber-related gigabit is termed 1000BASE-X, whereas 1000BASE-T gigabit ethernet uses twisted-pair (see the "Unshielded Twisted Pair " section, later in this chapter).
Wireless networking, as the name states, works without network cables and is an extremely popular option, particularly for those whose spouses do not like wires trailing everywhere! Upgrading is as easy as replacing network cards and equipment, such as routers and switches. Wireless networking equipment can also work along with the traditional wired networking using existing equipment.
It might not be practical to upgrade a desktop or large server to wireless just yet if the wiring is already in place. Wireless networking is still generally slower than a traditional wired network. However, this situation is changing with wider adoption of newer protocols, such as 802.11g (supporting the common 802.11b and faster but less popular 802.11a), along with the introduction of more compliant and inexpensive wireless NICs. Some 802.11g NICs work at up to 108Mbps, which appears faster than 100BASE-T wired networking on the surface. However, in practice, it is a great deal slower: Unless your networking environment has paper-thin walls, you can usually halve the reported speed of Wi-Fi network devices. 108Mbps works about half the speed of 100BASE-T.
With each new version of Linux, more and more wireless NICs are compatible. That said, it is usually better to get brand name wireless NICs, because you have a better chance of compatibility. Check the http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux/ web page for more specific hardware compatibility information. More on wireless networking is discussed later in this chapter.
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