From 2168ea8b1650198e0b91215adc5ad52c42651440 Mon Sep 17 00:00:00 2001 From: Robby Workman Date: Mon, 11 Jan 2010 23:22:22 -0600 Subject: Initial commit of the slackbook sources from Alan's master copy. --- chapter_13.xml | 403 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 403 insertions(+) create mode 100644 chapter_13.xml (limited to 'chapter_13.xml') diff --git a/chapter_13.xml b/chapter_13.xml new file mode 100644 index 0000000..23eae86 --- /dev/null +++ b/chapter_13.xml @@ -0,0 +1,403 @@ + + + + +Networking + +
+<application>netconfig</application> + + +Computers aren't very interesting on their own. Sure, you can install +games on them, but that just turns them into glorified entertainment +consoles. Today, computers need to be able to talk to one another; they +need to be networked. Whether you're installing a business network with +hundreds or thousands of computers or just setting up a single PC for +Internet access, Slackware is simple and easy. This chapter should +teach you how to setup typical wired networks. Common wireless setup will +be thoroughly discussed in the next section, but much of what you read +here will be applicable there as well. + + + +There are many different ways to configure your computer to connect to +a network or the Internet, but they fall into two main categories: +static and dymanic. Static addresses are solid; they are set with the +understanding that they will not be changed, at least not anytime soon. +Dynamic addresses are fluid; the assumption is that the address will +change at some time in the future. Typically any sort of network server +requires a static address simply so other machines will know where to +contact it when they need services. Dynamic addresses tend to be used +for workstations, Internet clients, and any machine that doesn't +require a static address for any reason. Dynamic addresses are more +flexible, but present complications of their own. + + + +There are many different kinds of network protocols that you might +encounter, but most people will only ever need to deal with Internet +Protocol (IP). For that reason, we'll focus exclusively on IP in this +book. + + +
+ +
+Manual Configuration + + +Ok, so you've installed Slackware, you've setup a desktop, but you +can't get it to connect to the Internet or your business's LAN (local +area network), what do you do? Fortunately, the answer to that question +is simple. Slackware includes a number of tools to configure your +network connection. The first we will look at today is the very +powerful ifconfig(8). +ifconfig is used to setup or modify the +configuration of a Network Interface Card (NIC or Ethernet Card), the +most common hardware for connecting to networks today. +ifconfig is an incredibly powerful tool +capable of doing much more than setting IP addresses. For a complete +introduction, you should read its man page. For now, we're just going +to use it to display and change the network addresses of some ethernet +controllers. + + +darkstar:~# ifconfig +lo Link encap:Local Loopback + inet addr:127.0.0.1 Mask:255.0.0.0 + inet6 addr: ::1/128 Scope:Host + UP LOOPBACK RUNNING MTU:16436 Metric:1 + RX packets:699 errors:0 dropped:0 overruns:0 frame:0 + TX packets:699 errors:0 dropped:0 overruns:0 carrier:0 + collisions:0 txqueuelen:0 + RX bytes:39518 (38.5 KiB) TX bytes:39518 (38.5 KiB) + +wlan0 Link encap:Ethernet HWaddr 00:1c:b3:ba:ad:4c + inet addr:192.168.1.198 Bcast:192.168.1.255 Mask:255.255.255.0 + inet6 addr: fe80::21c:b3ff:feba:ad4c/64 Scope:Link + UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 + RX packets:1630677 errors:0 dropped:0 overruns:0 frame:0 + TX packets:1183224 errors:0 dropped:0 overruns:0 carrier:0 + collisions:0 txqueuelen:1000 + RX bytes:1627370207 (1.5 GiB) TX bytes:163308463 (155.7 MiB) + +wmaster0 Link encap:UNSPEC HWaddr 00-1C-B3-BA-AD-4C-00-00-00-00-00-00-00-00-00-00 + UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 + RX packets:0 errors:0 dropped:0 overruns:0 frame:0 + TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 + collisions:0 txqueuelen:1000 + RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) + + + + +As you can clearly see here, when run without any arguments, +ifconfig will display all the information it +has on all the ethernet cards (and wireless ethernet cards) present on +your system. The above represents a typical wireless connection from my +laptop, so don't be afraid if what you see on your system doesn't +match. If you don't see any ethX or wlanX interfaces though, the +interface may be down. To show all currently present NICs whether they are +"up" or "down", simply pass the -a argument. + + +darkstar:~# ifconfig -a +eth0 Link encap:Ethernet HWaddr 00:19:e3:45:90:44 + UP BROADCAST MULTICAST MTU:1500 Metric:1 + RX packets:122780 errors:0 dropped:0 overruns:0 frame:0 + TX packets:124347 errors:0 dropped:0 overruns:0 carrier:0 + collisions:0 txqueuelen:1000 + RX bytes:60495452 (57.6 MiB) TX bytes:17185220 (16.3 MiB) + Interrupt:16 + +lo Link encap:Local Loopback + inet addr:127.0.0.1 Mask:255.0.0.0 + inet6 addr: ::1/128 Scope:Host + UP LOOPBACK RUNNING MTU:16436 Metric:1 + RX packets:699 errors:0 dropped:0 overruns:0 frame:0 + TX packets:699 errors:0 dropped:0 overruns:0 carrier:0 + collisions:0 txqueuelen:0 + RX bytes:39518 (38.5 KiB) TX bytes:39518 (38.5 KiB) + +wlan0 Link encap:Ethernet HWaddr 00:1c:b3:ba:ad:4c + inet addr:192.168.1.198 Bcast:192.168.1.255 Mask:255.255.255.0 + inet6 addr: fe80::21c:b3ff:feba:ad4c/64 Scope:Link + UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 + RX packets:1630677 errors:0 dropped:0 overruns:0 frame:0 + TX packets:1183224 errors:0 dropped:0 overruns:0 carrier:0 + collisions:0 txqueuelen:1000 + RX bytes:1627370207 (1.5 GiB) TX bytes:163308463 (155.7 MiB) + +wmaster0 Link encap:UNSPEC HWaddr 00-1C-B3-BA-AD-4C-00-00-00-00-00-00-00-00-00-00 + UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 + RX packets:0 errors:0 dropped:0 overruns:0 frame:0 + TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 + collisions:0 txqueuelen:1000 + RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) + + +Notice that the eth0 interface is now listed among the returns. +ifconfig can also change the current +settings on a NIC. Typically, you would need to change the IP address +and subnet mask, but you can change virtually any parameters. + + +darkstar:~# ifconfig eth0 192.168.1.1 netmask 255.255.255.0 +darkstar:~# ifconfig eth0 +eth0 Link encap:Ethernet HWaddr 00:19:e3:45:90:44 + inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0 + UP BROADCAST MULTICAST MTU:1500 Metric:1 + RX packets:122780 errors:0 dropped:0 overruns:0 frame:0 + TX packets:124347 errors:0 dropped:0 overruns:0 carrier:0 + collisions:0 txqueuelen:1000 + RX bytes:60495452 (57.6 MiB) TX bytes:17185220 (16.3 MiB) + Interrupt:16 + + + +If you look carefully, you'll notice that the interface now has the +192.168.1.1 IP address and a 255.255.255.0 subnet mask. We've now setup +the basics for connecting to our network, but we still need to setup a +default gateway and our DNS servers. In order to do that, we'll need to +look at a few more tools. + + + +Next on our stop through networking land is the equally powerful +route(8). This tool is responsible for +modifying the Linux kernel's routing table which affects all data +transmission on a network. Routing tables can become immensely complex +or they can be straight-forward and simple. Most users will only ever +need to setup a default gateway, so we'll show you how to do that here. +If for some reason you need a more complex routing table, you would be +well advised to read the entire man page for +route as well as consulting other sources. +For now, let's take a look at our routing table immediately after +setting up eth0. + + +darkstar:~# route +Kernel IP routing table +Destination Gateway Genmask Flags Metric Ref Use Iface +192.168.1.0 * 255.255.255.0 U 0 0 0 eth0 +loopback * 255.0.0.0 U 0 0 0 lo + + + +I won't explain everything here, but the general information should be +easy to pick up if you're familiar with networking at all. The +Destination and Genmask fields specify a range of IP addresses to +match. If a Gateway is defined, information in the form of packets will +be sent to that host for forwarding. We also specify an interface in +the final field that the information should traverse. Right now, we can +only communicate with computers with addresses between 192.168.1.0 and +192.168.1.255 and ourselves through the loopback interface, a type of +virtual NIC that is used for routing information from this computer to +itself. In order to reach the rest of the world, we'll need to +setup a default gateway. + + +darkstar:~# route add default gw 192.168.1.254 +darkstar:~# route +Kernel IP routing table +Destination Gateway Genmask Flags Metric Ref Use Iface +192.168.1.0 * 255.255.255.0 U 0 0 0 eth0 +loopback * 255.0.0.0 U 0 0 0 lo +default 192.168.1.254 0.0.0.0 UG 0 0 0 eth0 + + + +You should immediately notice the addition of a default route. This +specifies what router should be used to reach any addresses that aren't +specified elsewhere in our routing table. Now, when we try to connect +to say, 64.57.102.34, the information will be sent to 192.168.1.254 +which is responsible for delivering the data for us. Unfortunately, +we're still not quite through. We need some way of converting domain +names like slackware.com into IP addresses that the computer can use. +For that, we need to make use of a DNS server. + + + +Fortunately, setting up your computer to use an external (or even an +internal) DNS server is very easy. You'll need to use your favorite +text editor and open the /etc/resolv.conf file. +Don't ask me what happened to the e. On my computer, +resolv.conf looks like this. + + + +# /etc/resolv.conf +search lizella.net +nameserver 192.168.1.254 + + + +Most users won't need the "search" line. This is used to map hostnames +to domain names. Basically, if I attempt to connect to "barnowl", the +computer knows to look for "barnowl.lizella.net" thanks to this search +line. We're mainly interested in the "nameserver" line. This tells +Slackware what domain name servers (DNS) to connect to. Generally +speaking, these should always be specified by IP address. If you know +what DNS servers you should use, you can just add them one at a time to +individual nameserver lines. In fact, I don't know of any practical +limit to the number of nameservers that can be specified in +resolv.conf, so add as many as you like. Once this +is done, you should be able to communicate with other hosts via their +fully qualified domain name. + + + +But Alan! That's a lot of hard work! I don't want to do this time and +again for dozens or even hundreds of machines. You're absolutely right, +and that's why smarter people than you and me created DHCP. DHCP +stands for Dynamic Host Control Protocol and is a method for +automatically configuring computers with unique IP addresses, netmasks, +gateways, and DNS servers. Most of the time, you'll want to use DHCP. +The majority of wireless routers, DSL or cable modems, even firewalls +all have DHCP servers to can make your life much easier. Slackware +includes two main tools for connecting to an exising DHCP server and +can even act as a DHCP server for other computers. For now though, +we're just going to look at DHCP clients. + + + +First on our list is dhcpcd(8), part of the +ISC DHCP utilities. Assuming your computer is physically connected to +your network, and that you have an operating DHCP server on that +network, you can configure your NIC in one shot. + + +darkstar:~# dhcpcd eth0 + + + +If everything went according to plan, your NIC should be properly +configured, and you should be able to communicate with other computers +on your network, and with the Internet at large. If for some reason, +dhcpcd fails, you may want to try +dhclient(8). +dhclient is an alternative to +dhcpcd and works in basically the same way. + + +darkstar:~# dhclient eth0 +Listening on LPF/eth0/00:1c:b3:ba:ad:4c +Sending on LPF/eth0/00:1c:b3:ba:ad:4c +Sending on Socket/fallback +DHCPREQUEST on eth0 to 255.255.255.255 port 67 +DHCPACK from 192.168.1.254 +bound to 192.168.1.198 -- renewal in 8547 seconds. + + + +So why does Slackware include two DHCP clients? Sometimes a particular +DHCP server may be broken and not respond well to either +dhcpcd or +dhclient. In those cases, you can fall back +to the other DHCP client in hopes of getting a valid response from the +server. Traditionally, Slackware uses +dhcpcd, and this works in the vast majority +of cases, but it may become necessary at some point for you to use +dhclient instead. Both are excellent DHCP +clients, so use whichever you prefer. + + +
+ +
+Automatic Configuration with rc.inet1.conf + + +Manually configuring interfaces is an important skill to have, but it +can become tedious. No one wants to manually setup their Internet +connection every time the system boots. More importantly, you may not +always have physical access to the machine when it boots. Slackware +makes it easy to automatically configure ethernet (and wireless) cards +at system startup with /etc/rc.d/rc.inet1.conf. +For now, we're going to focus on traditional wired ethernet networking; +the next chapter will discuss various wireless options. + + + +rc.inet1.conf is an incredibly powerful +configuration file, capable of configuring most of your network cards +automatically when Slackware is started. The file is filled with useful +comments, but there is also a man page that more thoroughly discusses +its use. To begin, we're going to look at some of the options used on +one of my personal machines. + + + +# Config information for eth0: +IPADDR[0]="192.168.1.250" +NETMASK[0]="255.255.255.0" +USE_DHCP[0]="" +DHCP_HOSTNAME[0]="" +# Some lines ommitted. +GATEWAY="192.168.1.254" + + + +This represents most of the information necessary to configure a static +IP address on a single ethernet controller. +netconfig will usually fill in these values +for a single ethernet device for you. If you have multiple network +cards in your machine and need all of them activated automatically at +boot time, then you'll need to edit or add additional entries into this +file in the same manner as above. First, let me go over some of the +basics. + + + +As you may have already guessed, IPADDR[n] is the Internet Protocol +Address for the "n" network interface card. Typically, "n" corrosponds +to eth0, eth1, and so on, but this isn't always the case. You can +specify these values to pertain to a different network controller with +the INFAME[n] variable, but we will reserve that for the next chapter +on wireless networking, as it more commonly pertains to wireless +network controllers. Likewise, NETMASK[n] is the subnet mask to use +for the network controller. If these lines are left empty, then static +IP addresses will not be automatically assigned to this network +controller. The USE_DHCP[n] variable tells Slackware to (naturally) +use DHCP to configure the interface. DHCP_HOSTNAME[n] is rarely used, +but some DHCP servers may require it. In that case, it must be set to +a valid hostname. Finally, we come to the GATEWAY variable. It is +actually set lower in the file than it appears in my example, and it +controls the default gateway to use. You may be wondering why there is +no GATEWAY[n] variable. The answer to that lies in how Internet +Protocol works. I won't go into an indepth discussion on that subject, +but suffice it to say that there is only ever one default route that a +computer can use no matter how many interfaces are attached to it. + + + +If you need to use static IP addressing, you will have to obtain a +unique static IP address and the subnet mask for the interface, as well +as the default gateway address, and enter those here. There is no place +to enter DNS information in rc.inet1.conf, so DNS +servers will have to be manually placed into +resolv.conf as we discussed above. Of course, if +you use netconfig, this will be handled for +you by that program. Now let's take a look at another interface on my +computer. + + + +# Config information for eth1: +IPADDR[1]="" +NETMASK[1]="" +USE_DHCP[1]="yes" +DHCP_HOSTNAME[1]="" + + + +Here I am telling Slackware to configure eth1 using DHCP. I do not need +to set the IPADDR[1] or NETMASK[1] variables when using DHCP (in fact, +if they are set, they will be ignored). Slackware will happily contact +a DHCP server as soon as the machine begins to boot. + + +
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