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Configuring a
Static IP Address
Although DHCP is a common method of
configuration on many networks, it''s not used universally. It''s awkward to
configure some systems (such as DHCP servers) via DHCP, and some networks
simply lack DHCP servers. In these situations, you''ll need to configure your
computer''s IP address manually. This section describes how to do this, starting
with the tools to do the job a single time. The section entitled "
automatically whenever it reboots.
NOTE
align=left border=0> Traditionally, server computers have used
static IP address assignment, because this ensures that the computer''s IP address
won''t change. This fact is important for mapping hostnames (such as mail.threeroomco.com ) to IP addresses (such as 172.23.45.67) via a DNS server, as
described in
Administering a Domain via DNS. As described in
though, it''s possible to assign the same address to a computer time after
time via DHCP. There are also dynamic DNS services
that permit the mapping of a hostname onto a dynamic IP address.
Configuring
Network Interfaces
Loading a driver, as described earlier in
this chapter, is the first step in making a network interface available. To use
the interface, you must assign it an IP address and associated information,
such as its network mask (also called the subnet mask or netmask). This
job is handled by the ifconfig
utility, which displays information on an interface or changes its
configuration, depending upon how it''s called.
Basic
ifconfig Syntax and Use
The ifconfig
utility''s syntax is deceptively simple:
ifconfig [ interface ] [ options ]
The program behaves differently depending upon what parameters
it''s given. On a broad level, ifconfig
can do several different things:
If used without any parameters, ifconfig
returns the status of all currently active network interfaces. Used in this
way, ifconfig is a helpful
diagnostic tool.
If given a single interface name (such as eth0 or tr1 ),
ifconfig returns information on
that interface only. Again, this is a useful diagnostic tool.
If fed options in addition to an interface name, ifconfig modifies the interface''s
operation according to the options'' specifications. Most commonly, this means
activating or deactivating an interface.
If you''re using ifconfig
to configure an interface, you''ll be most concerned with the options you can
pass to the utility. The utility''s man page gives a complete listing of
options, but the most important are the following:
up address This option activates an
interface and associates the specified IP address with the new interface. If
the command doesn''t also include a netmask
option (described shortly), ifconfig
assigns a netmask based on the class of the address, as shown in
omit the up keyword; ifconfig assumes this if you give it an
interface name and IP address.
down This
option is the opposite of up ; it
closes down an interface.
netmask nm This option sets the network
mask of the interface, which determines which bits of the IP address correspond
to a network address and which identify a specific computer on a network. If
this option is omitted, ifconfig
sets the netmask to a default value, as shown in
the number of bits of network address in part of the up address
option, as described shortly.
[-]promisc
Ordinarily, a network card accepts only those packets that are directed at it,
or at all systems on its network segment. This option enables ( promisc ) or disables ( -promisc ) promiscuous
mode, in which the card reads all
network packets that traverse its local network segment. Promiscuous mode is
necessary for packet sniffers, which can be used as network diagnostic tools.
(Crackers also use packet sniffers to acquire passwords that are sent
unencrypted.) Some programs can enable promiscuous mode themselves. The default
is to bring up an interface in nonpromiscuous mode.
Table 2.2. Traditional TCP/IP
Classes and Their Network Masks
Class
Address Range
Private Address Range
Netmask
Class A
1.0.0.0127.255.255.255
10.0.0.010.255.255.255
255.0.0.0
Class B
128.0.0.0191.255.255.255
172.16.0.0172.31.255.255
255.255.0.0
Class C
192.0.0.0223.255.255.255
192.168.0.0192.168.255.255
255.255.255.0
mtu n This option sets the Maximum
Transfer Unit (MTU) of an interface, which is the maximum size of low-level
data packets. For Ethernet networks, the MTU is normally 1500, but you can set
it to something else if you like. (Some routers and protocols use smaller MTUs,
which can degrade performance if your system''s MTU is set higher, because your
larger packets will have to be broken up and sent as multiple packets.) add address/prefixlength This option
is the equivalent of up and netmask , but works with IPv6, the
next-generation Internet standard. As described in
than does the current IPv4. In 2002, IPv6 is still uncommon, but it''s likely to
become important in coming years.
del address/prefixlength This option
is the opposite of add ; it
removes an IPv6 address from the interface.
media type Some network cards include
two or more media connectors (for instance, connectors for 10Base-2 and
10Base-T cabling). You can specify which connector you want to use with this
option, as in media 10baseT .
Consult the driver''s documentation for details about what type values it accepts.
hw class address This option allows
you to control the hardware address of the network card. You might want to
change this if you''ve replaced one network card with another but want to use
the old hardware address to continue receiving the same IP address from a DHCP
server, for instance. Also, manufacturers occasionally slip up and ship a large
number of cards with identical hardware addresses, which can wreak havoc if you
try to use several such cards on a single network. This option requires two
suboptions: the class of
the network device (such as ether
for Ethernet or ARCnet for
ARCnet) and the hardware address .
This function works with many, but not all, network cards.
txqueulen length This option sets the
length of the transmit queue, which is the number of packets the interface will
attempt to queue together. The default for Ethernet devices is 100, which
usually works well. Setting a lower transmit queue length on slow connections
may improve interactive performance (say, for a Telnet or SSH session).
In most cases, a simple ifconfig
command will suffice to activate an interface. For instance, the following
command activates the first Ethernet card with the address 172.23.45.67:
# ifconfig eth0 172.23.45.67
If you must use a more complex configuration, you may do so by
adding parameters to the command, such as:
# ifconfig eth0 172.23.45.67 netmask 255.255.255.0 mtu 1420
The netmask specifies which parts of an IP address correspond
to the network address, and which parts identify a specific computer. A
computer uses this information in determining how to address outgoing packets,
so setting it incorrectly can result in some computers being inaccessible. When
converted to binary, the netmask consists of a series of binary 1 values
followed by a series of binary 0 values. For instance, 255.255.255.0 is
twenty-four 1 values followed by eight 0 values. A shorthand notation for the
IP address and netmask is to follow the IP address with a slash ( / ) and the number of bits in the network
portion of the address. For instance, 172.23.45.67/24 is equivalent to
172.23.45.67 with a netmask of 255.255.255.0. You can use this notation as part
of the up addres option to ifconfig , instead of specifying a separate
netmask nm option.
IP Address Classes
These examples show activating a network interface in a
private address range, as shown in
for use on private networks; no Internet site uses these addresses. In order
to avoid accidentally using somebody''s IP address, I also use these private
addresses in my examples throughout this book. I use the 192.168.
x.x addresses in my examples as they''re intended,
but I use addresses in the 172.16.0.0172.31.255.255 and 10.
x.x.x ranges as if they were routable Internet
addresses.
In addition to Classes AC shown in
D is used for multicasts (traffic destined for
multiple hosts), and Class E is reserved for future use.
Although IP address netmasks have traditionally been
assigned as shown in
have become increasingly common in the 1990s and later. This is because the
initial allocation scheme had too many huge Class A networks and too few
Class C networks. Deviations from the netmasks shown in
arbitrary assignment of netmasks to IP address ranges. For instance, an ISP
might ask for a couple of Class C networks, and be given addresses that are
traditionally part of a Class A network, such as 10.34.56.0/24 and
10.34.57.0/24. By carving up these networks, the existing range of IP
addresses is extended further than it could be by strict adherence to the
Class AC designations. The downside is that people who enter IP address
information must take care to specify the netmasks for these addresses. If
you let ifconfig set the
netmask automatically for, say, 10.34.56.78, the netmask will be set to 255.0.0.0,
which is wrong. Given its allocation method, the netmask should probably be
255.255.255.0.
Configuring
Multiple Network Interfaces
If a computer has multiple network interfaces, you must issue
the ifconfig command once for
each interface. For instance, you might issue the following two commands:
# ifconfig eth0 up 192.168.1.1 # ifconfig eth1 up 172.23.45.67/24
These commands configure eth0
on the 192.168.1.1 address (presumably for a local private network), and eth1 on 172.23.45.67, using a netmask of
255.255.255.0. Both interfaces will then function. How, though, does the
computer know to which interface to send any given network packet? For
instance, suppose a program tries to contact the computer at 10.9.8.7. Over
which interface should Linux send this packet? It''s the job of the routing table to answer this question. In fact, this
question is important even for a single-interface computer, as described shortly.
Adjusting
the Routing Table
The routing table directs traffic in two ways. First, it tells
Linux over what interface to send traffic. This may seem obvious in a
single-interface computer, but Linux supports a special virtual interface known
as the localhost or loopback
interface. This interface uses the 127.0.0.0/8 network, but it''s usually
addressed using just one IP address: 127.0.0.1. Because this interface exists
on all computers, programs can use it when they need to use networking
protocols to interface to other local programs. It''s also faster than using the
computer''s regular network interface. Rules must exist to properly direct
traffic to the localhost interface or the physical interface (and to a particular physical interface, if a computer has more
than one). The second job of the routing table is to direct traffic that''s
destined for other computers on the local network, as opposed to computers that
are located on remote networks and thus must be routed. In the case of local
network traffic, Linux can use the Address Resolution Protocol (ARP) to
communicate directly with the destination system, but remote targets need to be
handled by a router or gateway systema computer that passes packets from
one network to another. Most Linux systems'' routing tables list just one
gateway computer, but some complex configurations use multiple gateways.
Configuring the routing table is the job of the route command.
NOTE
align=left border=0> The path between two arbitrary computers on the Internet
typically includes a dozen or more routers, but your computer needs to know
only the address of the first of these, and of the destination system. The
first router knows how to reach the next one, and so on until the final
destination computer is reached.
Understanding Routing
Table Structure
The routing table consists of a series of entries specifying
what to do with packets sent to certain ranges of IP addresses. When a program
sends an outgoing packet to the kernel, the kernel compares the destination address
to the destination address ranges in the routing table, starting with the most
specific destination address ranges (that is, those that define the smallest
networks). If the packet''s destination matches one of these ranges, it''s sent
in the way specified by the routing table rule. If not, the next rule is
checked. Normally, the most general rule in the routing table is known as the default route, which matches any address. The default route normally directs
packets through the local network''s gateway computer.
To understand this better, it may help to examine a sample
routing table.
routing table, on one system. (The route
command is discussed in more detail in the next section, "
from the most to the least specific. The first entry, for a destination of
255.255.255.255, is for broadcasts. These go out over the eth0 interface and do not involve a
gateway. The next two entries, for destinations of 10.92.68.0 and 192.168.1.0,
represent local network traffic for networks with netmasks of 255.255.255.0 (as
shown in the Genmask column).
Network addresses usually end in 0, but the network portion of the address is
defined by the netmask, as described earlier. These entries send traffic to the
eth1 and eth0 interfaces, respectively; a computer
with just one network interface would probably have only one entry of this
form. The fourth entry, for 127.0.0.0, is the localhost interface, as described
earlier. (Some distributions, such as Debian, don''t explicitly show this route,
but it still works.) Note its interface device (in the Iface column) is lo . The final entry, for a destination of
0.0.0.0, is the default route. This address, in conjunction with the netmask of
0.0.0.0, matches any traffic that has not already been matched. It sends
traffic over the eth1 interface,
and it''s the only route in this sample that uses a gateway10.92.68.1 in this
case.
Figure 2.2. You can determine how
Linux will route a packet by comparing its destination address to the Destination and Genmask columns of the routing table.
one entry for the interface to your routing table. This entry corresponds to
the local network route for the interface (the routes with netmasks of
255.255.255.0 in
automatically add the localhost interface entry. The broadcast entry (for
255.255.255.255) is not required or active on most systems, but some utilities
need this entry. In normal operation, the main routing table entry that''s left
to be defined is the one for the default route.
Basic
route Syntax and Use
If it''s given without any parameters, or with only certain
parameters like -n (which
produces numeric output rather than hostnames for entries like the gateway
systems), route displays the
current routing table. You can also use this tool to add, delete, or change
routing table entries. To do this, you use route
with additional parameters. The syntax for such use is as follows:
route add | del [-net | -host] target [netmask nm ] [gateway gw ] [metric m ] [mss m ] [window W ] [[dev] interface ]
Each of these parameters has a specific meaning:
add | del
Specify add if you want to add a
route, or del if you want to
delete one. In either case, you must give enough information for route to act on the route. (For deletions,
you can usually get away with nothing more than the target .) [-net | -host]
You can specify a target address as either a network ( -net ) or a single computer ( -host ). In most cases, route can figure this out for itself, but
sometimes it needs prompting. This is particularly likely if you''re adding a
route for a second gateway (like a gateway that only handles one small subnet,
rather than the default route''s gateway).
target
The target address is the computer or network whose packets should be defined
by the route. In the case of the default route, this will be 0.0.0.0 , or the equivalent keyword, default . This parameter is required when
you add or delete a route.
[netmask nm ] If your target network follows the traditional class
structure for network addresses, Linux can determine what the netmask should
be. If your network doesn''t follow this pattern, though, you must include the netmask nm parameter, in which you give route the netmask. (Alternatively, you can
include this information with the target address as the number of bits in the
network component, as described earlier.) [gateway gw ] If you''re adding a route that doesn''t involve a
gateway, you can omit this parameter. If you want to specify a gateway system,
though, you must include the gateway
gw parameter. You''ll use
this to define the default gateway or any other gateway system.
[metric m ] If you examine
"cost" of delivery, which is normally associated with time. Slow
routes should have high metrics, whereas fast routes should have low metrics.
You can set this feature with the metric
m parameter. This feature
is normally only used on router computers, as described in
[mss m ] The mss
m option sets the Maximum
Segment Size (MSS). Like the metric
m option, this option is
useful primarily on routers.
[window W ] The TCP Window Size
is the amount of data that a computer will send before it requires an
acknowledgment from the recipient. If this value is set too small, network
transfers may be slowed because the system will end up waiting for
acknowledgments before sending new data. If it''s set too high, the risk of
having to re-send a lot of data because of errors will be increased. As a
general rule, Linux''s default TCP Window size of 64KB is acceptable. If your
system uses a connection that''s fast but that has very high latencies, such as
a satellite broadband connection, you might consider raising this to 128KB or
so.
[[dev] interface ] Usually, Linux can figure out what
interface to use from the target IP address or the gateway system''s address.
This might not always be true, though, and in such cases, you can force the
issue by using the [dev] interface parameter. (The dev keyword is optional, and interface is the interface name, such
as eth0 or tr1 .) The most common use of route
is to add the default route after adding the primary network interface using ifconfig . This use is fairly simple, as
illustrated by this example:
# route add 0.0.0.0 gw 10.92.68.1
If you prefer, you can substitute the keyword default for 0.0.0.0 ; the two have precisely the same effect. On rare
occasions, you must add a -net
specification, device name, or some other option.
Multiple
Interfaces with One Gateway
As noted earlier, each time you add an interface with ifconfig , that utility automatically adds
an entry to your routing table for that interface. This does not extend to
adding a gateway, however. As a consequence, the configuration required on many
computers with multiple interfaces consists of two types of action:
1.
Run
ifconfig for each of the
computer''s interfaces.
2.
Run
route once to add the computer''s
default route to the routing table.
This set of steps will be adequate for a small router, such as
a Linux computer that functions as a router for a small department in a larger
organization. For a router, you''ll also have to enable routing by turning on IP
forwarding. You can do this by typing the following command:
# echo "1" > /proc/sys/net/ipv4/ip_forward
NOTE
align=left border=0> If the computer has two interfaces but should not function as a router, you should not enable IP forwarding. This might be the case if
a computer exists on two networks that should not communicate with each
other, or that use some other computer as a router.
NOTE
align=left border=0> Routing duties shouldn''t ordinarily be performed by a
computer that does other work. Non-routing tasks can consume CPU time and
network bandwidth that can degrade the router''s performance. There are also
potential security issues; routers today often include firewall features, and
running unnecessary software on a firewall leaves an avenue of attack open.
If you have just one external IP address but want to connect
several computers to the Internet, you can use a special type of routing known
as Network Address Translation (NAT).
technology. The basic steps are the same as for a normal router, but NAT
requires you to run extra commands to allow the router to translate addresses
in order to make your entire network look like a single computer to the outside
world.
Multiple
Interfaces with Multiple Gateways
A trickier configuration is one in which a computer can use
multiple gateways. Most systems use just one gateway, which is associated with the
default route. The gateway ties the local network to some other network, and
often ultimately to the Internet. There are other configurations possible,
however. For instance, consider
in which an organization has connected two subnetworks via routers. The regular
computers in both offices can be configured quite simplythey need only point
to their local routers as their gateways. Likewise, the router in Office 2 can
point to the router in Office 1 as its sole gateway system, although the Office
2 router has two interfaces, as just discussed. The router in Office 1,
however, requires a more complex configuration. Its default route leads to the
Internet, but it must also configure a route to the Office 2 router for traffic
destined for the 172.20.0.0/16 network. You might use a route command like the following to
accomplish this goal:
# route add -net 172.20.0.0 netmask 255.255.0.0 gw 172.21.1.1
Figure 2.3. Routers with more than
two interfaces require at least two gateway definitions in order to function
properly.
align=left border=0> A configuration like this makes the most sense when Office 1
and Office 2 are widely separated geographically and are linked by some form
of long-distance network protocol. If the offices were located close
together, both might be tied into a single hub or switch and served by a
single router.
This command assumes that Office 2''s router talks to Office
1''s router using the 172.21.1.1 address. (Note that this address is not part of
the Office 2 network proper; it''s on a different network card in Office 2''s
router.) The end result of issuing this command as well as a normal route command to define the default route
will be a routing table that includes two gateways: one for the default route
and one to handle traffic destined to Room 2''s systems. None of the other
computers that link to Office 1''s router need to know anything about this
arrangement; they only need to know that this router is the gateway for the
default route.
There are other situations in which a similar configuration
might be required. For instance, if Office 1 used a second router to link to
the Internet, all of the computers in Office 1 would need to have two gateways
defined: one default route pointing to the system that leads to the Internet,
and a second route pointing to the router that leads to Office 2.
(Alternatively, regular systems could list just one router, which could pass
traffic to the other router when appropriate, but this would increase local
network traffic.) Because a network with two routers involves more tricky
configuration for all computers on the network, it''s best to use a single
router on any given subnet whenever possible.
Configuring
DNS
Once an interface is active and a gateway set, a computer can
send and receive network traffic destined for anywhere on its local network or
any other network to which the gateway connects, directly or indirectly.
Traffic must be addressed by IP address, though, which is tedious at best. It''s
the job of the Domain Name System (DNS) to
provide a better user interface by converting the alphanumeric names (such as www.awl.com ) used by people to
IP addresses used by computers. (DNS can also do the reverse conversion.) DNS is a globally distributed database, but any given computer
needs to know just one IP address to gain entry to that database: the address
of a single DNS server. Most organizations and ISPs provide at least one DNS
server, and many provide two or three. You should consult your network
administrator to learn the addresses of your network''s DNS servers. When you''ve
obtained this information, you can enter it into the /etc/resolv.conf file. This file can have
up to three lines that begin with the keyword nameserver
and end with the IP address of a DNS server. The file can also specify the
default domain of the Linux system (using the domain
keyword) and an arbitrary number of domains that are to be searched when you
omit a domain name (for instance, if you specify mail rather than mail.threeroomco.com ) using the search keyword.
three keywords.
Listing
2.1 An example /etc/resolv.conf file
domain threeroomco.com search tworoomco.com fourroomco.com nameserver 10.98.17.34 nameserver 172.20.13.109
WARNING
align=left border=0> Although the search
option makes it possible to reduce typing by omitting the specified domain
names when performing network accesses, this option should be used sparingly.
The problem is that two domains may have identically named computers, and
this could lead to confusion. For instance, if tworoomco.com and fourroomco.com both have Web servers called www , a user who types www in a Web browser on a computer with
it''s the other domain''s Web server. These searches also take time, so most
other name lookups will be slowed down. Normally, even when you specify a
complete name, the system searches for that name first in the domains
specified by the domain and search lines. For instance, if a user
types www.awl.com ,
www.awl.com.tworoomco.com ,
and www.awl.com.fourroomco.com ,
and only then to search for www.awl.com .
This final (correct) search can be done first by including a period at the
end of the domain name, as in www.awl.com. .
Once you''ve edited /etc/resolv.conf
to your liking, there''s no command needed to activate the changes. Linux will
simply begin using the specified name servers and searching the specified
domains.
If you want Linux to function as a DNS server for your
network, consult
on running a DNS server, which can be used by other computers on your own
network, by computers on the Internet at large, or by both, depending upon the
server''s configuration.
Setting
the Hostname
Many TCP/IP protocols require that computers identify
themselves by name to each other. To simplify configuration of individual
programs, Linux maintains a global hostname setting, which can be viewed or set
with the hostname command.
Typing the command alone displays the current hostname. Typing the command
followed by a hostname (as in hostnamelarch.threeroomco.com )
sets the hostname to the specified name. You can store the hostname in a file
and pass that file to the hostname
command with the -F or file option, as in hostname -f /etc/HOSTNAME . Most
distributions do this automatically at boot time, although the location of the
hostname varies from one distribution to another. Check /etc/ hostname , /etc/HOSTNAME , and the files listed in the
Extra Configuration Files column of
Unfortunately, although the ideal is to set the hostname once,
this isn''t always possible. Some user-level programsparticularly e-mail
clients and Usenet news readersallow users to override the default hostname
setting. You or your users may therefore need to set the hostname in these
programs, particularly if you ever change the hostname. You might also want to
set the hostname in /etc/hosts .
This file exists as a method of name resolution that''s an alternative to DNS.
It consists of lines that begin with an IP address and continue with a series
of hostnames. Most commonly, the first hostname is a Fully-Qualified
Domain Name (FQDN) that is, a complete hostname, including the machine
name and the domain to which it belongs, as in larch.threeroomco.com . Subsequent names on the same
line are "nicknames"normally shortened forms, such as larch . If your system''s DNS settings are
correct, and if your computer has appropriate entries in your network''s DNS
server, it won''t be necessary to create an /etc/hosts
entry for the computer. If your network''s DNS servers, or the network path to
those servers, is unreliable, however, creating an /etc/hosts entry for your computer can improve overall
reliability. You might also want to ensure that the 127.0.0.1 address is
represented, with hostnames of localhost.localdomain
and localhost . Examples of both
entries might resemble the following:
10.92.68.1 larch.threeroomco.com larch 127.0.0.1 localhost.localdomain localhost
TIP
align=left border=0> If the computer pauses for several seconds or even minutes during
the boot process, particularly when starting sendmail, chances are you need
to set entries such as those mentioned above in your /etc/hosts file, or you need to fix your
network''s DNS server entries for the computer. Some programs, including
sendmail, pause for long periods of time if they can''t connect their
hostnames and IP addresses via DNS, /etc/hosts ,
or some other method.
If a computer has multiple network interfaces, you''ll set one
hostname using the hostname
command, but you''ll normally create multiple hostnames, one for each interface,
in the /etc/hosts file, although
this isn''t required. (Your network''s DNS servers will also normally have two or
more names for the computer in this case.) TIP
align=left border=0> On a small private network, you can use /etc/hosts to handle all your local
hostnames, obviating the need to run a DNS server for local computers only.
This practice becomes tedious as a network grows in size, though, so many
larger networks use a centralized DNS server.
Making Your Changes Permanent
Some of the preceding procedures, such as adjusting hostnames
in /etc/hosts and setting up
name server addresses in /etc/resolv.conf ,
involve editing configuration files. These changes are permanent; once you make
them, you won''t need to make them again unless your configuration files become
damaged or you reinstall Linux. Other changes, by contrast, are transient in
nature. When you run ifconfig , route , or hostname
to adjust a system feature, that change will last only as long as the computer
runs or until it''s undone by another action. If you reboot, the change will be
lost. In order to make such a change permanent, you must adjust a startup
script or configuration file, either by editing the file in a text editor or by
using a GUI configuration tool.
Using
a GUI Configuration Tool
One of the easiest ways to make a permanent change in a
network setting is to do it with a GUI configuration toolat least, if your
distribution includes such a tool. (Debian and Slackware both eschew the use of
such tools.) Specific options include the following:
Red Hat and Mandrake These distributions use a GUI configuration tool called Linuxconf,
which is also used by some other distributions, such as LinuxPPC. The user
interface differs slightly from one distribution to another. You can launch
this tool by typing linuxconf . It operates in text mode using text-based menus, in GUI mode using
GUI menus, and in an optional Web server mode to permit remote administration.
SuSE SuSE uses Yet Another Setup Tool (YaST) as a menu-driven
text-based tool, and YaST2 as a GUI counterpart to YaST. (
YaST2 in operation.) Type yast or yast2 to launch these tools.
Caldera Caldera uses the Caldera Open Administration System (COAS) as its
GUI setup tool. It can be launched by typing coastool in an xterm
window.
TurboLinux TurboLinux uses the TurboLinux Configuration Center for a GUI
configuration tool. You can launch it by typing turbocfgcenter .
All Distributions The Webmin project ( target="_blank">http://www.webmin.com/webmin/ ) is a Web-based administration tool that can be used with many
different Linux distributions and non-Linux Unix-like systems. It''s not
installed by default with most distributions, but if your distribution is
supported by Webmin, getting it running shouldn''t be too difficult.
The exact details differ from one tool to
another, but to configure a system using GUI tools, you must normally locate a
network configuration menu, and possibly delve another layer or two into the
interface to locate the settings you need to alter. You then enter the
configuration options you want to set permanently. For instance, in
can click Static Address Setup and enter the IP address and netmask in the
fields provided, then click the Hostname and Nameserver button and the Routing
button to adjust these features.
One drawback to GUI tools is that they
sometimes don''t permit more advanced configurations. For instance, there might
be no way to adjust a routing table with the precision required for
configurations like those discussed earlier, in the section "
configurations, though. If you have trouble with the GUI tools, you can resort
to directly editing the configuration files.
Editing Configuration Files
the locations of configuration files in which DHCP client commands and extra
configuration information are listed. These files also hold commands and
configurations for handling static IP addresses. You should peruse these files,
looking for calls to ifconfig , route , hostname , or other configuration commands. Some files don''t include
commands, but instead set environment variables that hold information such as
whether the system uses DHCP or a static IP address configuration, and hold the
static configuration information in the latter case. A perusal of the scripts
and configuration files involved should be enough to let you configure your
system.
Should you encounter problems with the normal
configuration scripts, one way to force the issue is to create entries in a
local startup script that call the configuration commands you want to use. Most
distributions use /etc/rc.d/rc.local as a local startup script, but SuSE uses /etc/rc.d/ boot.local . Debian has no single local startup script, but you can create such
a file in the /etc/rc.boot directory. When you create or edit such a script, you can enter any
commands you like, including network commands like ifconfig and route . These
commands will execute after other startup scripts, though, so this isn''t the
ideal location for most network configuration commands. It might be an
acceptable way to get the system to add an unusual route, however, such as a
gateway route for a single small subnet, as discussed earlier.
