Manual configuration of the network software should always be the last alternative. Using YaST is recommended. However, this background information about the network configuration can also assist your work with YaST.
When the kernel detects a network card and creates a corresponding network interface, it assigns the device a name depending on the order of device discovery, or order of the loading of the kernel modules. The default kernel device names are only predictable in very simple or tightly controlled hardware environments. Systems which allow adding or removing hardware during runtime or support automatic configuration of devices cannot expect stable network device names assigned by the kernel across reboots.
However, all system configuration tools rely on persistent interface
names. The problem is solved by udev. The udev persistent net generator
(/lib/udev/rules.d/75-persistent-net-generator.rules)
generates a rule matching the hardware (using its hardware address by
default) and assigns a persistently unique interface for the hardware. The
udev database of network interfaces is stored in the file
/etc/udev/rules.d/70-persistent-net.rules. Every line
in the file describes one network interface and specifies its persistent
name. System administrators can change the assigned names by editing the
NAME="" entries. The persistent rules can also be
modified using YaST.
Table 21.5, “Manual Network Configuration Scripts” summarizes the most important scripts involved in the network configuration.
Table 21.5. Manual Network Configuration Scripts
|
Command |
Function |
|---|---|
|
ifup, ifdown, ifstatus |
The |
|
rcnetwork |
The |
For more information about udev and persistent device names, see Chapter 19, Dynamic Kernel Device Management with udev.
This section provides an overview of the network configuration files and explains their purpose and the format used.
These files contain the configurations for network interfaces. They
include information such as the start mode and the IP address. Possible
parameters are described in the manual page of
ifup. Additionally, most variables from the
files dhcp, wireless and
config can be used in the
ifcfg-* files if a general setting should be used
for only one interface.
For ifcfg.template, see
Section 21.6.1.2, “/etc/sysconfig/network/config, /etc/sysconfig/network/dhcp, and /etc/sysconfig/network/wireless”.
The file config contains general settings for the
behavior of ifup, ifdown and
ifstatus. dhcp contains settings
for DHCP and wireless for wireless LAN cards. The
variables in all three configuration files are commented. Some of the
variables from /etc/sysconfig/network/config can
also be used in ifcfg-* files, where they are given
a higher priority. The
/etc/sysconfig/network/ifcfg.template file lists
variables that can be specified in a per interface scope. However, most
of the /etc/sysconfig/network/config variables are
global and cannot be overriden in ifcfg-files. For example
NETWORKMANAGER or
NETCONFIG_* variables are global.
The static routing of TCP/IP packets is determined here. All the static
routes required by the various system tasks can be entered in the
/etc/sysconfig/network/routes file: routes to a
host, routes to a host via a gateway and routes to a network. For each
interface that needs individual routing, define an additional
configuration file:
/etc/sysconfig/network/ifroute-*. Replace
* with the name of the interface. The entries in the
routing configuration files look like this:
# Destination Dummy/Gateway Netmask Device # 127.0.0.0 0.0.0.0 255.255.255.0 lo 204.127.235.0 0.0.0.0 255.255.255.0 eth0 default 204.127.235.41 0.0.0.0 eth0 207.68.156.51 207.68.145.45 255.255.255.255 eth1 192.168.0.0 207.68.156.51 255.255.0.0 eth1
The route's destination is in the first column. This column may contain the IP address of a network or host or, in the case of reachable name servers, the fully qualified network or hostname.
The second column contains the default gateway or a gateway through
which a host or network can be accessed. The third column contains the
netmask for networks or hosts behind a gateway. For example, the mask is
255.255.255.255 for a host
behind a gateway.
The fourth column is only relevant for networks connected to the local host such as loopback, Ethernet, ISDN, PPP and dummy device. The device name must be entered here.
An (optional) fifth column can be used to specify the type of a route.
Columns that are not needed should contain a minus sign
- to ensure that the parser correctly interprets the
command. For details, refer to the routes(5)
man page.
The domain to which the host belongs is specified in this file (keyword
search). Also listed is the status of the name
server address to access (keyword nameserver).
Multiple domain names can be specified in the file. When resolving a
name that is not fully qualified, an attempt is made to generate one by
attaching the individual search entries.
Multiple name servers can be specified in multiple lines, each beginning
with nameserver. Comments are preceded by
# signs. Example 21.5, “/etc/resolv.conf”
shows what /etc/resolv.conf could look like.
However, the /etc/resolv.conf should not be edited
by hand. Instead, it is generated by the netconfig
script. To define static DNS configuration without using YaST, edit
the appropriate variables manually in the
/etc/sysconfig/network/config file:
NETCONFIG_DNS_STATIC_SEARCHLIST (list of DNS
domain names used for hostname lookup),
NETCONFIG_DNS_STATIC_SERVERS (list of name
server IP addresses to use for hostname lookup),
NETCONFIG_DNS_FORWARDER (defines the name of
the DNS forwarder that has to be configured). To disable DNS
configuration using netconfig, set
NETCONFIG_DNS_POLICY=''. For more information about
netconfig, see man 8 netconfig.
Example 21.5. /etc/resolv.conf
# Our domain search example.com # # We use dns.example.com (192.168.1.116) as nameserver nameserver 192.168.1.116
netconfig is a modular tool to manage additional network configuration settings. It merges statically defined settings with settings provided by autoconfiguration mechanisms as dhcp or ppp according to a predefined policy. The required changes are applied to the system by calling the netconfig modules that are responsible for modifying a configuration file and restarting a service or a similar action.
netconfig recognizes three main actions. The netconfig modify and netconfig remove commands are used by daemons such as dhcp or ppp to provide or remove settings to netconfig. Only the netconfig update command is available for the user:
- modify
The netconfig modify command modifies the current interface and service specific dynamic settings and updates the network configuration. Netconfig reads settings from standard input or from a file specified with the
--lease-fileoption and internally stores them until a system reboot (or the next modify or remove action). Already existing settings for the same interface and service combination are overwritten. The interface is specified by thefilename-iparameter. The service is specified by theinterface_name-sparameter.service_name- remove
The netconfig remove command removes the dynamic settings provided by a modificatory action for the specified interface and service combination and updates the network configuration. The interface is specified by the
-iparameter. The service is specified by theinterface_name-sparameter.service_name- update
The netconfig update command updates the network configuration using current settings. This is useful when the policy or the static configuration has changed.
The netconfig policy and the static configuration settings are defined
either manually or using YaST in the
/etc/sysconfig/network/config file. The dynamic
configuration settings provided by autoconfiguration tools as dhcp or
ppp are delivered directly by these tools with the netconfig
modify and netconfig remove actions. NetworkManager
also uses netconfig modify and netconfig
remove actions. When NetworkManager is enabled, netconfig (in policy
mode auto) uses only NetworkManager settings, ignoring settings
from any other interfaces configured using the traditional ifup method.
If NetworkManager does not provide any setting, static settings are used as a
fallback. A mixed usage of NetworkManager and the traditional ifup method is not
supported.
For more information about netconfig, see man 8 netconfig.
In this file, shown in Example 21.6, “/etc/hosts”, IP
addresses are assigned to hostnames. If no name server is implemented,
all hosts to which an IP connection will be set up must be listed here.
For each host, enter a line consisting of the IP address, the fully
qualified hostname, and the hostname into the file. The IP address must
be at the beginning of the line and the entries separated by blanks and
tabs. Comments are always preceded by the # sign.
Example 21.6. /etc/hosts
127.0.0.1 localhost 192.168.2.100 jupiter.example.com jupiter 192.168.2.101 venus.example.com venus
Here, network names are converted to network addresses. The format is
similar to that of the hosts file, except the
network names precede the addresses. See
Example 21.7, “/etc/networks”.
Name resolution—the translation of host and network names via the
resolver library—is controlled by this file.
This file is only used for programs linked to libc4 or libc5. For
current glibc programs, refer to the settings in
/etc/nsswitch.conf. A parameter must always stand
alone in its own line. Comments are preceded by a #
sign. Table 21.6, “Parameters for /etc/host.conf” shows the parameters
available. A sample /etc/host.conf is shown in
Example 21.8, “/etc/host.conf”.
Table 21.6. Parameters for /etc/host.conf
|
order hosts, bind |
Specifies in which order the services are accessed for the name resolution. Available arguments are (separated by blank spaces or commas): |
|
hosts: searches the
| |
|
bind: accesses a name server | |
|
nis: uses NIS | |
|
multi on/off |
Defines if a host entered in |
|
nospoof on spoofalert on/off |
These parameters influence the name server spoofing but do not exert any influence on the network configuration. |
|
trim domainname |
The specified domain name is separated from the hostname after
hostname resolution (as long as the hostname includes the domain
name). This option is useful only if names from the local domain
are in the |
Example 21.8. /etc/host.conf
# We have named running order hosts bind # Allow multiple address multi on
The introduction of the GNU C Library 2.0 was accompanied by the
introduction of the Name Service Switch (NSS).
Refer to the nsswitch.conf(5) man page and
The GNU C Library Reference Manual for details.
The order for queries is defined in the file
/etc/nsswitch.conf. A sample
nsswitch.conf is shown in
Example 21.9, “/etc/nsswitch.conf”. Comments are preceded by
# signs. In this example, the entry under the
hosts database means that a request is sent to
/etc/hosts (files) via
DNS.
Example 21.9. /etc/nsswitch.conf
passwd: compat group: compat hosts: files dns networks: files dns services: db files protocols: db files netgroup: files automount: files nis
The “databases” available over NSS are listed in
Table 21.7, “Databases Available via /etc/nsswitch.conf”. In addition,
automount, bootparams,
netmasks and publickey are
expected in the near future. The configuration options for NSS databases are listed in
Table 21.8, “Configuration Options for NSS “Databases””.
Table 21.7. Databases Available via /etc/nsswitch.conf
|
|
Mail aliases implemented by |
|
|
Ethernet addresses. |
|
|
For user groups used by |
|
|
For hostnames and IP addresses, used by
|
|
|
Valid host and user lists in the network for the purpose of
controlling access permissions; see the
|
|
|
Network names and addresses, used by
|
|
|
User passwords, used by |
|
|
Network protocols, used by |
|
|
Remote procedure call names and addresses, used by
|
|
|
Network services, used by |
|
|
Shadow passwords of users, used by |
Table 21.8. Configuration Options for NSS “Databases”
|
|
directly access files, for example,
|
|
|
access via a database |
|
|
NIS, see also Chapter Using NIS (↑Security Guide) |
|
|
can only be used as an extension for |
|
|
can only be used as an extension for |
This file is used to configure nscd (name service cache daemon). See the
nscd(8) and
nscd.conf(5) man pages. By default, the system
entries of passwd and groups are
cached by nscd. This is important for the performance of directory
services, like NIS and LDAP, because otherwise the network connection
needs to be used for every access to names or groups.
hosts is not cached by default, because the mechanism
in nscd to cache hosts makes the local system unable to trust forward
and reverse lookup checks. Instead of asking nscd to cache names, set up
a caching DNS server.
If the caching for passwd is activated, it usually
takes about fifteen seconds until a newly added local user is
recognized. Reduce this waiting time by restarting nscd with the command
rcnscd restart.
Before you write your configuration to the configuration files, you can test it. To set up a test configuration, use the ip command. To test the connection, use the ping command. Older configuration tools, ifconfig and route, are also available.
The commands ip, ifconfig and route change the network configuration directly without saving it in the configuration file. Unless you enter your configuration in the correct configuration files, the changed network configuration is lost on reboot.
ip is a tool to show and configure routing, network devices, policy routing and tunnels.
ip is a very complex tool. Its common syntax is
ip options
object
command
- link
This object represents a network device.
- address
This object represents the IP address of device.
- neighbour
This object represents a ARP or NDISC cache entry.
- route
This object represents the routing table entry.
- rule
This object represents a rule in the routing policy database.
- maddress
This object represents a multicast address.
- mroute
This object represents a multicast routing cache entry.
- tunnel
This object represents a tunnel over IP.
If no command is given, the default command is used (usually list).
Change the state of a device with the command ip link
set device_namecommand.
For example, to deactivate device eth0, enter ip link
set eth0 down. To activate it again, use
ip link set eth0 up.
After activating a device, you can configure it. To set the IP address,
use ip addr
add ip_address + dev
device_namebrd), enter ip
addr add 192.168.12.154/30 brd + dev
eth0.
To have a working connection, you must also configure the default
gateway. To set a gateway for your system, enter ip route
add gateway_ip_address. To translate one
IP address to another, use nat: ip route add
nat ip_address via other_ip_address.
To display all devices, use ip link ls. To display
the running interfaces only, use ip link ls up. To
print interface statistics for a device, enter ip -s link
ls device_name. To view addresses of
your devices, enter ip addr. In the output of the
ip addr, also find information about MAC addresses of
your devices. To show all routes, use ip route show.
For more information about using ip, enter
ip help or see the
ip(8) man page. The help
option is also available for all ip objects. If, for example, you want
to read help for ip addr, enter
ip addr help. Find the ip
manual in
/usr/share/doc/packages/iproute2/ip-cref.pdf.
The ping command is the standard tool for testing whether a TCP/IP connection works. It uses the ICMP protocol to send a small data packet, ECHO_REQUEST datagram, to the destination host, requesting an immediate reply. If this works, ping displays a message to that effect, which indicates that the network link is basically functioning.
ping does more than test only the function of the connection between two computers: it also provides some basic information about the quality of the connection. In Example 21.10, “Output of the Command ping”, you can see an example of the ping output. The second-to-last line contains information about number of transmitted packets, packet loss, and total time of ping running.
As the destination, you can use a hostname or IP address, for example,
ping example.com or
ping 192.168.3.100. The program sends
packets until you press
Ctrl+C.
If you only need to check the functionality of the connection, you can
limit the number of the packets with the -c option. For
example to limit ping to three packets, enter
ping -c 3 example.com.
Example 21.10. Output of the Command ping
ping -c 3 example.com PING example.com (192.168.3.100) 56(84) bytes of data. 64 bytes from example.com (192.168.3.100): icmp_seq=1 ttl=49 time=188 ms 64 bytes from example.com (192.168.3.100): icmp_seq=2 ttl=49 time=184 ms 64 bytes from example.com (192.168.3.100): icmp_seq=3 ttl=49 time=183 ms --- example.com ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2007ms rtt min/avg/max/mdev = 183.417/185.447/188.259/2.052 ms
The default interval between two packets is one second. To change the
interval, ping provides option -i. For example to
increase ping interval to ten seconds, enter
ping -i 10 example.com.
In a system with multiple network devices, it is sometimes useful to
send the ping through a specific interface address. To do so, use the
-I option with the name of the selected device, for
example, ping -I wlan1
example.com.
For more options and information about using ping, enter
ping -h or see the
ping (8) man page.
ifconfig is a traditional network configuration tool. In contrast to ip, you can use it only for interface configuration. If you want to configure routing, use route.
![[Note]](admon/note.png) | ifconfig and ip |
|---|---|
The program ifconfig is obsolete. Use ip instead. | |
Without arguments, ifconfig displays the status of the currently active
interfaces. As you can see in
Example 21.11, “Output of the ifconfig Command”, ifconfig has very
well-arranged and detailed output. The output also contains information
about the MAC address of your device (the value of
HWaddr) in the first line.
Example 21.11. Output of the ifconfig Command
eth0 Link encap:Ethernet HWaddr 00:08:74:98:ED:51
inet6 addr: fe80::208:74ff:fe98:ed51/64 Scope:Link
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:634735 errors:0 dropped:0 overruns:4 frame:0
TX packets:154779 errors:0 dropped:0 overruns:0 carrier:1
collisions:0 txqueuelen:1000
RX bytes:162531992 (155.0 Mb) TX bytes:49575995 (47.2 Mb)
Interrupt:11 Base address:0xec80
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:8559 errors:0 dropped:0 overruns:0 frame:0
TX packets:8559 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:533234 (520.7 Kb) TX bytes:533234 (520.7 Kb)
wlan1 Link encap:Ethernet HWaddr 00:0E:2E:52:3B:1D
inet addr:192.168.2.4 Bcast:192.168.2.255 Mask:255.255.255.0
inet6 addr: fe80::20e:2eff:fe52:3b1d/64 Scope:Link
UP BROADCAST NOTRAILERS RUNNING MULTICAST MTU:1500 Metric:1
RX packets:50828 errors:0 dropped:0 overruns:0 frame:0
TX packets:43770 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:45978185 (43.8 Mb) TX bytes:7526693 (7.1 MB)
For more options and information about using ifconfig, enter
ifconfig -h or see the
ifconfig (8) man page.
route is a program for manipulating the IP routing table. You can use it to view your routing configuration and add or remove of routes.
| route and ip |
|---|---|
The program route is obsolete. Use ip instead. | |
route is especially useful if you need quick and comprehensible
information about your routing configuration to determine problems with
routing. To view your current routing configuration, enter
route -n as root.
Example 21.12. Output of the route -n Command
route -n Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 10.20.0.0 * 255.255.248.0 U 0 0 0 eth0 link-local * 255.255.0.0 U 0 0 0 eth0 loopback * 255.0.0.0 U 0 0 0 lo default styx.exam.com 0.0.0.0 UG 0 0 0 eth0
For more options and information about using route, enter
route -h or see the
route (8) man page.
Apart from the configuration files described above, there are also various scripts that load the network programs while the machine is booting. These are started as soon as the system is switched to one of the multiuser runlevels. Some of these scripts are described in Table 21.9, “Some Start-Up Scripts for Network Programs”.
Table 21.9. Some Start-Up Scripts for Network Programs
|
This script handles the configuration of the network interfaces. If the network service was not started, no network interfaces are implemented. | |
|
Starts xinetd. xinetd can be used to make server services available on the system. For example, it can start vsftpd whenever an FTP connection is initiated. | |
|
Starts the rpcbind utility that converts RPC program numbers to universal addresses. It is needed for RPC services, such as an NFS server. | |
|
Starts the NFS server. | |
|
Controls the postfix process. | |
|
Starts the NIS server. | |
|
Starts the NIS client. |