Linux network commands December 16, 2010Posted by Tournas Dimitrios in Linux.
Tags: Linux network commands
Linux, which is based on Unix, is a network operating system. It is an operating system designed to serve end user systems such as workstation and personal computer.
Linux also provide other important network services including printer sharing, database sharing, ftp, NFS , webserver , FTP ,routing, firewall and so on.
In this article , user will learn from basic network configuration which is configuring network interface card to the advanced server configuration.
The command line utilities that will be covered are :
- Linux ifconfig command
- Linux netstat command
- Basic ftp command
- Linux route command
- Linux ping command
- Install and using Lynx web browser in CentOs
A newcomer to the world of Linux may be scared from the different jargons , but promise you , with a little :) exercise , these commands will become a second nature to you .
The ifconfig command : Ifconfig command is used to configure network interfaces. ifconfig stands for interface configurator. Ifconfig is widely used to initialize the network interface and to enable or disable the interfaces.
|The ifconfig command
|ifconfig eth0||Ifconfig, when invoked with no arguments will display all the details of currently active interfaces. If you give the interface name as an argument, the details of that specific interface will be displayed.|
|ifconfig -a||Display Details of All interfaces Including Disabled Interfaces|
|ifconfig eth0 192.168.2.2||Assign 192.168.2.2 as the IP address for the interface eth0.|
|ifconfig eth0 netmask 255.255.255.0||Change Subnet mask of the interface eth0.|
|ifconfig eth0 broadcast 192.168.2.255||Change Broadcast address of the interface eth0.|
|ifconfig eth0 mtu XX||This will change the Maximum transmission unit (MTU) to XX. MTU is the maximum number of octets the interface is able to handle in one transaction. For Ethernet the Maximum transmission unit by default is 1500.|
The netstat command : Linux netstat command is another useful network utility in Linux. We can use netstat to list network connections, view routing table and information about network interface. The netstat command has been one of useful tools for network troubleshooting. This tutorial is a basic guide to the netstat command with usage examples to help the new Linux beginner.
|The netstat command
|netstat -[aisl]||Lists all listening and non-listening sockets using netstat command with -a option:
Displays statistics for Linux network interfaces using netstat command with -i option:
Lists listening sockets using netstat command with -l option:
Displays summary information for each protocol using netstat command with -s option:
|netstat -r||Displays Linux routing table using netstat command with -r option:|
|netstat -ap | grep ssh||Find out on which port a program is running|
|netstat -ie||Display extended information on the interfaces (similar to ifconfig) using netstat -ie:|
|netstat -c||Print netstat information continuously|
|netstat -an||When you don’t want the name of the host, port or user to be displayed, use netstat -n option. This will display in numbers, instead of resolving the host name, port name, user name.|
|netstat -[tu]||Display only ports related to the udp / tcp protocol|
|netstat -pt||netstat -p option can be combined with any other netstat option. This will add the “PID/Program Name” to the netstat output. This is very useful while debugging to identify which program is running on a particular port.|
|netstat -s[tu]||Show the statistics for each protocol tcp and or udp|
The route command : Besides Linux ifconfig command, the Linux route command is another important network commands every Linux user should know. The route command can be used to add or modify a static route and a default gateway in the Linux or Unix system. As specify in the Linux Programmer’s Manual, Linux route command shows or manipulate the IP routing table. The IP stated is the Internet Protocol (ip address, netmask, gateway) which has been set during configuring network interface card (NIC) in the Linux ifconfig table earlier.
The Linux route command comes with many options but most network administrators familiar with add and del options. The route add command is used to add a new route while the route del command is to delete a route.
|The route command
|route add -net 192.168.1.0 netmask 255.255.255.0 dev eth0||To add a new ip route via eth0 (first Ethernet card), issue route add command in this format:|
|route add -net 192.168.1.0 gw 192.168.1.1
netmask 255.255.255.0 dev eth0
|You can also add a gateway:|
|route||Show the routing table|
|route -n||Show the routing table in numeric format|
route add -net 127.0.0.0
adds the normal loopback entry, using netmask 255.0.0.0 (class
A net, determined from the destination address) and associated
with the “lo” device (assuming this device was prviously set up
correctly with ifconfig(8)).
route add -net 220.127.116.11 netmask 255.255.255.0 dev eth0
adds a route to the network 192.56.76.x via “eth0”. The Class C
netmask modifier is not really necessary here because 192.* is a
Class C IP address. The word “dev” can be omitted here.
route add default gw mango-gw
adds a default route (which will be used if no other route
matches). All packets using this route will be gatewayed
through “mango-gw”. The device which will actually be used for
that route depends on how we can reach “mango-gw” – the static
route to “mango-gw” will have to be set up before.
route add ipx4 sl0
Adds the route to the “ipx4” host via the SLIP interface (assum-
ing that “ipx4” is the SLIP host).
route add -net 18.104.22.168 netmask 255.255.255.0 gw ipx4
This command adds the net “192.57.66.x” to be gatewayed
through the former route to the SLIP interface.
route add -net 22.214.171.124 netmask 240.0.0.0 dev eth0
This is an obscure one documented so people know how to do
it. This sets all of the class D (multicast) IP routes to go via
“eth0”. This is the correct normal configuration line with a
route add -net 10.0.0.0 netmask 255.0.0.0 reject
This installs a rejecting route for the private network
The output of the kernel routing table is organized in the following
The destination network or destination host.
The gateway address or ‘*’ if none set.
The netmask for the destination net; ‘255.255.255.255’ for a
host destination and ‘0.0.0.0’ for the default route.
Flags Possible flags include
U (route is up)
H (target is a host)
G (use gateway)
R (reinstate route for dynamic routing)
D (dynamically installed by daemon or redirect)
M (modified from routing daemon or redirect)
A (installed by addrconf)
C (cache entry)
! (reject route)
The ‘distance’ to the target (usually counted in hops). It is
not used by recent kernels, but may be needed by routing
Ref Number of references to this route. (Not used in the Linux ker-
Use Count of lookups for the route. Depending on the use of -F
and -C this will be either route cache misses (-F) or hits (-C).
Iface Interface to which packets for this route will be sent.
MSS Default maximum segement size for TCP connections over
Window Default window size for TCP connections over this route.
irtt Initial RTT (Round Trip Time). The kernel uses this to guess
about the best TCP protocol parameters without waiting on (pos-
sibly slow) answers.
HH (cached only)
The number of ARP entries and cached routes that refer to the
hardware header cache for the cached route. This will be -1 if a
hardware address is not needed for the interface of the cached
route (e.g. lo).
Arp (cached only)
Whether or not the hardware address for the cached route
is up to date.