10.2.1. Configuration of network interfacesAll the big, userfriendly Linux distributions come with various graphical tools, allowing for easy setup of the computer in a local network, for connecting it to an Internet Service Provider or for wireless access. These tools can be started up from the command line or from a menu: Show
Your system documentation provides plenty of advice and information about availability and use of tools. Information that you will need to provide:
10.2.2. Network configuration filesThe graphical helper tools edit a specific set of network configuration files, using a couple of basic commands. The exact names of the configuration files and their location in the file system is largely dependent on your Linux distribution and version. However, a couple of network configuration files are common on all UNIX systems: 10.2.2.1. /etc/hostsThe /etc/hosts file always contains the localhost IP address, 127.0.0.1, which is used for interprocess communication. Never remove this line! Sometimes contains addresses of additional hosts, which can be contacted without using an external naming service such as DNS (the Domain Name Server). A sample hosts file for a small home network: # Do not remove the following line, or various programs # that require network functionality will fail. 127.0.0.1 localhost.localdomain localhost 192.168.52.10 tux.mylan.com tux 192.168.52.11 winxp.mylan.com winxp Read more in man hosts. 10.2.2.2. /etc/resolv.confThe /etc/resolv.conf file configures access to a DNS server, see Section 10.3.7. This file contains your domain name and the name server(s) to contact: search mylan.com nameserver 193.134.20.4 Read more in the resolv.conf man page. 10.2.2.3. /etc/nsswitch.confThe /etc/nsswitch.conf file defines the order in which to contact different name services. For Internet use, it is important that dns shows up in the "hosts" line: [bob@tux ~] grep hosts /etc/nsswitch.conf hosts: files dns This instructs your computer to look up hostnames and IP addresses first in the /etc/hosts file, and to contact the DNS server if a given host does not occur in the local hosts file. Other possible name services to contact are LDAP, NIS and NIS+. More in man nsswitch.conf. 10.2.3. Network configuration commands10.2.3.1. The ip commandThe distribution-specific scripts and graphical tools are front-ends to ip (or ifconfig and route on older systems) to display and configure the kernel's networking configuration. The ip command is used for assigning IP addresses to interfaces, for setting up routes to the Internet and to other networks, for displaying TCP/IP configurations etcetera. The following commands show IP address and routing information: benny@home benny> ip addr show 1: lo: <LOOPBACK,UP> mtu 16436 qdisc noqueue link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 brd 127.255.255.255 scope host lo inet6 ::1/128 scope host 2: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 100 link/ether 00:50:bf:7e:54:9a brd ff:ff:ff:ff:ff:ff inet 192.168.42.15/24 brd 192.168.42.255 scope global eth0 inet6 fe80::250:bfff:fe7e:549a/10 scope link benny@home benny> ip route show 192.168.42.0/24 dev eth0 scope link 127.0.0.0/8 dev lo scope link default via 192.168.42.1 dev eth0 Things to note:
10.2.3.2. The ifconfig commandWhile ip is the most novel way to configure a Linux system, ifconfig is still very popular. Use it without option for displaying network interface information: els@asus:~$ /sbin/ifconfig eth0 Link encap:Ethernet HWaddr 00:50:70:31:2C:14 inet addr:60.138.67.31 Bcast:66.255.255.255 Mask:255.255.255.192 inet6 addr: fe80::250:70ff:fe31:2c14/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:31977764 errors:0 dropped:0 overruns:0 frame:0 TX packets:51896866 errors:0 dropped:0 overruns:0 carrier:0 collisions:802207 txqueuelen:1000 RX bytes:2806974916 (2.6 GiB) TX bytes:2874632613 (2.6 GiB) Interrupt:11 Base address:0xec00 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:765762 errors:0 dropped:0 overruns:0 frame:0 TX packets:765762 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:624214573 (595.2 MiB) TX bytes:624214573 (595.2 MiB) Here, too, we note the most important aspects of the interface configuration:
Both ifconfig and ip display more detailed configuration information and a number of statistics about each interface and, maybe most important, whether it is "UP" and "RUNNING". 10.2.3.3. PCMCIA commandsOn your laptop which you usually connect to the company network using the onboard Ethernet connection, but which you are now to configure for dial-in at home or in a hotel, you might need to activate the PCMCIA card. This is done using the cardctl control utility, or the pccardctl on newer distributions. A usage example: cardctl insert Now the card can be configured, either using the graphical or the command line interface. Prior to taking the card out, use this command: cardctl eject However, a good distribution should provide PCMCIA support in the network configuration tools, preventing users from having to execute PCMCIA commands manually. 10.2.3.4. More informationFurther discussion of network configuration is out of the scope of this document. Your primary source for extra information is the man pages for the services you want to set up. Additional reading:
10.2.4. Network interface namesOn a Linux machine, the device name lo or the local loop is linked with the internal 127.0.0.1 address. The computer will have a hard time making your applications work if this device is not present; it is always there, even on computers which are not networked. The first ethernet device, eth0 in the case of a standard network interface card, points to your local LAN IP address. Normal client machines only have one network interface card. Routers, connecting networks together, have one network device for each network they serve. If you use a modem to connect to the Internet, your network device will probably be named ppp0. There are many more names, for instance for Virtual Private Network interfaces (VPNs), and multiple interfaces can be active simultaneously, so that the output of the ifconfig or ip commands might become quite extensive when no options are used. Even multiple interfaces of the same type can be active. In that case, they are numbered sequentially: the first will get the number 0, the second will get a suffix of 1, the third will get 2, and so on. This is the case on many application servers, on machines which have a failover configuration, on routers, firewalls and many more. 10.2.5. Checking the host configuration with netstatApart from the ip command for displaying the network configuration, there's the common netstat command which has a lot of options and is generally useful on any UNIX system. Routing information can be displayed with the -nr option to the netstat command: bob:~> netstat -nr Kernel IP routing table Destination Gateway Genmask Flags MSS Window irtt Iface 192.168.42.0 0.0.0.0 255.255.255.0 U 40 0 0 eth0 127.0.0.0 0.0.0.0 255.0.0.0 U 40 0 0 lo 0.0.0.0 192.168.42.1 0.0.0.0 UG 40 0 0 eth0 This is a typical client machine in an IP network. It only has one network device, eth0. The lo interface is the local loop.
When this machine tries to contact a host that is on another network than its own, indicated by the line starting with 0.0.0.0, it will send the connection requests to the machine (router) with IP address 192.168.42.1, and it will use its primary interface, eth0, to do this. Hosts that are on the same network, the line starting with 192.168.42.0, will also be contacted through the primary network interface, but no router is necessary, the data are just put on the network. Machines can have much more complicated routing tables than this one, with lots of different "Destination-Gateway" pairs to connect to different networks. If you have the occasion to connect to an application server, for instance at work, it is most educating to check the routing information. 10.2.6. Other hostsAn impressive amount of tools is focused on network management and remote administration of Linux machines. Your local Linux software mirror will offer plenty of those. It would lead us too far to discuss them in this document, so please refer to the program-specific documentation. We will only discuss some common UNIX/Linux text tools in this section. 10.2.6.1. The host commandTo display information on hosts or domains, use the host command: [emmy@pc10 emmy]$ host www.eunet.be www.eunet.be. has address 193.74.208.177 [emmy@pc10 emmy]$ host -t any eunet.be eunet.be. SOA dns.eunet.be. hostmaster.Belgium.EU.net. 2002021300 28800 7200 604800 86400 eunet.be. mail is handled by 50 pophost.eunet.be. eunet.be. name server ns.EU.net. eunet.be. name server dns.eunet.be. Similar information can be displayed using the dig command, which gives additional information about how records are stored in the name server. 10.2.6.2. The ping commandTo check if a host is alive, use ping. If your system is configured to send more than one packet, interrupt ping with the Ctrl+C key combination: [emmy@pc10 emmy]$ ping a.host.be PING a.host.be (1.2.8.3) from 80.20.84.26: 56(84) bytes of data. 64 bytes from a.host.be(1.2.8.3):icmp_seq=0 ttl=244 time=99.977msec --- a.host.be ping statistics --- 1 packets transmitted, 1 packets received, 0% packet loss round-trip min/avg/max/mdev = 99.977/99.977/99.977/0.000 ms 10.2.6.3. The traceroute commandTo check the route that packets follow to a network host, use the traceroute command: [emmy@pc10 emmy]$ /usr/sbin/traceroute www.eunet.be traceroute to www.eunet.be(193.74.208.177),30 hops max,38b packets 1 blob (10.0.0.1) 0.297ms 0.257ms 0.174ms 2 adsl-65.myprovider.be (217.136.111.1) 12.120ms 13.058ms 13.009ms 3 194.78.255.177 (194.78.255.177) 13.845ms 14.308ms 12.756ms 4 gigabitethernet2-2.intl2.gam.brussels.skynet.be (195.238.2.226) 13.123ms 13.164ms 12.527ms 5 pecbru2.car.belbone.be (194.78.255.118) 16.336ms 13.889ms 13.028ms 6 ser-2-1-110-ias-be-vil-ar01.kpnbelgium.be (194.119.224.9) 14.602ms 15.546ms 15.959ms 7 unknown-195-207-939.eunet.be (195.207.93.49) 16.514ms 17.661ms 18.889ms 8 S0-1-0.Leuven.Belgium.EU.net (195.207.129.1) 22.714ms 19.193ms 18.432ms 9 dukat.Belgium.EU.net (193.74.208.178) 22.758ms * 25.263ms On some systems, traceroute has been renamed to tracepath. 10.2.6.4. The whois commandSpecific domain name information can be queried using the whois command, as is explained by many whois servers, like the one below: [emmy@pc10 emmy]$ whois cnn.com [whois.crsnic.net] Whois Server Version 1.3 $<--snap server message--> Domain Name: CNN.COM Registrar: NETWORK SOLUTIONS, INC. Whois Server: whois.networksolutions.com Referral URL: http://www.networksolutions.com Name Server: TWDNS-01.NS.AOL.COM Name Server: TWDNS-02.NS.AOL.COM Name Server: TWDNS-03.NS.AOL.COM Name Server: TWDNS-04.NS.AOL.COM Updated Date: 12-mar-2002 >>> Last update of whois database: Fri, 5 Apr 2002 05:04:55 EST <<< The Registry database contains ONLY .COM, .NET, .ORG, .EDU domains and Registrars. [whois.networksolutions.com] $<--snap server message--> Registrant: Turner Broadcasting (CNN-DOM) 1 CNN Center Atlanta, GA 30303 Domain Name: CNN.COM Administrative Contact: $<--snap contactinfo--> Technical Contact: $<--snap contactinfo--> Billing Contact: $<--snap contactinfo--> Record last updated on 12-Mar-2002. Record expires on 23-Sep-2009. Record created on 22-Sep-1993. Database last updated on 4-Apr-2002 20:10:00 EST. Domain servers in listed order: TWDNS-01.NS.AOL.COM 149.174.213.151 TWDNS-02.NS.AOL.COM 152.163.239.216 TWDNS-03.NS.AOL.COM 205.188.146.88 TWDNS-04.NS.AOL.COM 64.12.147.120 For other domain names than .com, .net, .org and .edu, you might need to specify the whois server, such as this one for .be domains: whois Which command line tool would you use to view IP address configuration on a Unix system?To find out the IP address of Linux/UNIX/*BSD/macOS and Unixish system, you need to use the command called ifconfig on Unix and the ip command or hostname command on Linux. These commands used to configure the kernel-resident network interfaces and display IP address such as 10.8. 0.1 or 192.168. 2.254.
Which of the following is a Linux command line command used for configuring network interface parameters specific to the wireless communication?ifconfig can be used at the command line to configure (or re-configure) a network interface.
Which commands may be used to display the configured IP address information?The ipconfig command displays the basic IP addressing information for each network interface on the Windows system. This information includes both the IP address and subnet mask.
Which two commands can be used to resolve a FQDN to an IP address?dig and nslookup – these commands can be used to resolve FQDNs to IP addresses.
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