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Linux Networking Iowa State University Office of Academic Information Technology Linux Networking How Networking Works Configuring Networking in Linux Using redhat config network Network debugging Wireless networking IPv6 UNIX and the Internet grew up together In this class we ll look at UNIX networking as practiced in Linux beginning with the basics of how networking works We ll show you two ways to configure networking and how to debug network problems Finally we ll look briefly at wireless network setup and the future of the Internet Ipv6 There are a number of different protocols that can be used to communicate on a network but UNIX Networking uses the TCP IP protocol by default and therefore Linux has historically preferred the but Linux can use other protocols to interact with TCP IP protocol set Linux is ecumenical though other operating systems it can also communicate with Microsoft Windows Novell Netware and Mac OS through their MS Networking samba respective native protocols This class however Novell Netware ipx will concentrate on TCP IP and leave the others for AppleShare netatalk another time Networking Networking References Much more info on TCP IP available at Linux Network Administrator s Guide by Dawson Bautts and Purdy O Reilly http www redhat com docs manuals enterpris e RHEL 4 Manual sysadmin guide http www redhat com docs manuals enterpris e RHEL 4 Manual ref guide http www freeprogrammingresources com tcp html There are a number of good references to Linux networking The best I ve seen is the Linux Network Administrator s Guide available from O Reilly For Red Hat Linux the first two URLs are the manuals pertinent to networking The third URL is a good compendium of online tutorials on TCP IP Linux Networking Network Interfaces Page 2 Like most things in UNIX network interfaces are treated as files under the dev directory Unfortunately you can t just cat network devices and expect predictable results there are special commands for working with them All interfaces treated as devices found under dev devname lo loopback device loopback device It is used for testing purposes Used for testing and accessing servers running on and for accessing servers running on the local the local machine machine That s handy when you want to use Named localhost with IP 127 0 0 1 The first network device we ll discuss is lo the software that works with a Web or database server but you don t want it accessible by everyone on the Internet Ethernet and wireless cards are the most common network devices nowadays and Linux treats them identically giving them the names dev eth0 eth0 eth1 dev eth1 etc I ll probably lump them Ethernet and wireless cards together under Ethernet interfaces or network cards The software for Ethernet interfaces is Most common connections on campus usually loaded into the kernel during startup with the insmod command Some older network Drivers are usually loaded as a module during cards may not work or give reasonable startup using insmod but some older drivers may have to be compiled into the Linux kernel to performance unless their modules are compiled work correctly Usually detected at installation into the kernel unless you add them later The first Ethernet card will usually be detected when you install Linux but others will have to be added by hand If the Red Hat installer doesn t find it and you re not sure what it is try booting up a Knoppix disk The Knoppix hardware detection routines are really good Point to Point Protocol is used for Internet PPP interfaces connections over serial interfaces usually modems As a general rule making a PPP ppp0 ppp1 connection involves using an application like wvdial or kdial and the dev pppN device Point to point protocol usually telephone modem becomes active when the connection is actually made It s also possible to run a PPP daemon on Appears when you invoke the PPP client daemon a Linux machine to provide your own dialup usually by running something like wvdial or kdial to connect to an Internet service provider access but that s beyond the scope of this class Ethernet wireless interfaces Linux Networking Page 3 There are lots of other interfaces many of which are hardly ever used unless you re trying to make a connection to an old machine that doesn t have tk0 tk1 Token ring interfaces Ethernet available or you need to transfer the sl0 sl1 SLIP serial usually modem outdated Ethernet driver to in the first place In that case and replaced by PPP a LapLink parallel cable and a plip server easy enough to set up make for a relatively simple plip0 Parallel Line Interface Protocol connection between two machines parallel port like LapLink Other interfaces cipebc0 Crypto IP Encapsulation IP tunnel isdn0 ax0 ax1 AX 25 for amateur radio buffs ISDN modems Naming of Parts The terms I m using I m going to be discussing version 4 of the IP MAC Address hardware address of the NIC protocols so IP addresses are 32 bits long I ll assigned by the card manufacturer when the card touch on IPv6 which uses 128 bit addresses is made at the end of the course Ex 00 0a 95 a7 62 d8 IP Address 32 bit address relating machine to its physical location on the network also called IP number Contains the data to be transferred plus MAC addresses and IP addresses for both source and destination Header info IP Addresses Actual data to be transferred Header info includes packet identifier packet type protocol to be used time to live and checksum NIC Network Interface Card the hardware that That a MAC address has nothing to do with a connects the machine to the network might be Macintosh although all modern Macs do have built in to motherboard might be a PCI or ISA or MAC addresses PCCard addon IP Packet I include this slide just so you know This string of bytes is yelled on to the subnet and the router forwards it where it s supposed to go In the days of 10Base2 coax Ethernets and bridging hubs a subnet of computers was sort of like people in a crowded room When a machine wanted to send information somewhere it was transmitted to the subnet and all the machines on the subnet heard the packet go by Nowadays using switches instead of hubs the traffic from each machine goes to the switch and the switch forwards packets only to the machines they re intended for It s more secure because packet sniffing becomes impossible unless you can compromise the switch somehow and it makes your computer run better because it doesn t have to decide what to do with all

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