You can configure a network interface from the command line using the networking utilities. You configure your network client hosts with the command line by using commands to change your current settings or by editing a number of system files.
Configuring DHCP address for your network card
If you want to configure DHCP address you need to edit the /etc/network/interfaces and you need to enter the following lines replace eth0 with your network interface card
#vi /etc/network/interfaces
# The primary network interface - use DHCP to find our address
auto eth0
iface eth0 inet dhcp
Configuring Static IP address for your network card
If you want to configure Static IP address you need to edit the /etc/network/interfaces and you need to enter the following lines replace eth0 with your network interface card
#vi /etc/network/interfaces
# The primary network interface
auto eth0
iface eth0 inet static
address 192.168.3.90
gateway 192.168.3.1
netmask 255.255.255.0
network 192.168.3.0
broadcast 192.168.3.255
After entering all the details you need to restart networking services using the following command
#/etc/init.d/networking restart
Setting up Second IP address or Virtual IP address in Debian
If you are a server system administrator or normal user some time you need to assign a second ipaddress to your Ubuntu machine.For this you need to edit the /etc/network/interfaces file and you need to add the following syntax.Below one is the only example you need to chnage according to your ip address settings
#vi /etc/network/interfaces
auto eth0:1
iface eth0:1 inet static
address 192.168.1.60
netmask 255.255.255.0
network x.x.x.x
broadcast x.x.x.x
gateway x.x.x.x
You need to enter all the details like address,netmask,network,broadcast and gateways values after entering all the values save this file and you need to restart networking services in debian using the following command to take effect of our new ipaddress.
After entering all the details you need to restart networking services using the following command
#/etc/init.d/networking restart
Configure Network Interface Using ifconfig
You can configure a network interface from the command line using the basic Linux networking utilities. You configure your network client hosts with the command line by using commands to change your current settings or by editing a number of system files. Two commands, ifconfig and route, are used for network configuration. The netstat command displays information about the network connections.
ifconfig Advantages
ifconfig is used to configure your network interface. You can use it to
Activate or deactivate your NIC or change your NIC’s mode
Change your machine’s IP address, netmask, or broadcast address
Create an IP alias to allow more than one IP address on your NIC
Set a destination address for a point-to-point connection
Using ifconfig with Examples
If you want to find your current ip address you need to enter the following command
ifconfig
Output looks like below
eth0 Link encap:Ethernet HWaddr 00:0F:EA:B2:53:85
inet addr:192.168.2.5 Bcast:192.168.2.255 Mask:255.255.255.0
inet6 addr: fe80::20f:eaff:feb2:5385/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:471 errors:0 dropped:0 overruns:0 frame:0
TX packets:695 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:160637 (156.8 KiB) TX bytes:86193 (84.1 KiB)
Interrupt:185 Base address:0×6000
Create new network alias to a network card (NIC)
Syntax
ifconfig [network device]
Example
ifconfig eth0:1 172.30.49.4
Change IP address
ifconfig eth0 172.30.49.13
Change Subnetmask
Syntax
ifconfig netmask [netmask]
Example
ifconfig eth0 netmask 255.255.255.0
Change broadcast address
Syntax
ifconfig broadcast [address]
Example
ifconfig eth0 broadcast 172.30.49.1
Take interface down
Syntax
ifconfig [network device] down
Example
ifconfig eth0 down
Bring interface up
Syntax
ifconfig [network device] ipaddress up
Example
ifconfig eth0 172.30.49.13 up
If you want to know more information about ifconfig check man page
Setting your Debian stytem hostname
Setting up your hostname upon a debian installation is very straightforward. You can directly query, or set, the hostname with the hostname command.
As an user you can see your current hostname with
# /bin/hostname
Example
To set the hostname directly you can become root and run
#/bin/hostname newname
When your system boots it will automatically read the hostname from the file /etc/hostname
If you want to know more about how to setup host name check here
Setting up DNS
When it comes to DNS setup Debian doesn’t differ from other distributions. You can add hostname and IP addresses to the file /etc/hosts for static lookups.
To cause your machine to consult with a particular server for name lookups you simply add their addresses to /etc/resolv.conf.
For example a machine which should perform lookups from the DNS server at IP address 192.168.3.2 would have a resolv.conf file looking like this
#vi /etc/resolv.conf
enter the following details
search test.com
nameserver 192.168.3.2
Network Troubleshooting Tips
Networking is sometimes considered to be complex, and hard to troubleshoot and manage. However, Linux provides you with Some tools to figure out exactly what’s going wrong on your network, and how to fix it.Here we are going see some tools and how to check the network connectivity.
Ping
Ping is a computer network tool used to test whether a particular host is reachable across an IP network. Ping works by sending ICMP “echo request” packets to the target host and listening for ICMP “echo response” replies (sometimes dubbed “Pong!” as an analog from the Ping Pong table tennis sport.) Using interval timing and response rate, ping estimates the round-trip time (generally in milliseconds although the unit is often omitted) and packet loss (if any) rate between hosts.
This is very basic and powerful tool to check Internet connection
Example
#ping -c 4 google.com
-c option is used to pass how many packets you’re sending
If everything working file you should get reply looks like below
Pinging www.l.google.com [64.233.183.103] with 32 bytes of data:
Reply from 64.233.183.103: bytes=32 time=12ms TTL=244
Reply from 64.233.183.103: bytes=32 time=12ms TTL=244
Reply from 64.233.183.103: bytes=32 time=12ms TTL=244
Reply from 64.233.183.103: bytes=32 time=12ms TTL=244
Ping statistics for 64.233.183.103:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 12ms, Maximum = 12ms, Average = 12ms
Traceroute
traceroute is a computer network tool used to determine the route taken by packets across an IP network. An IPv6 variant, traceroute6, is also widely available.Very useful to trace IP packets.
Example
#traceroute google.com
ifconfig
The Unix command ifconfig can function as a tool to configure a network interface for TCP/IP from the command line interface (CLI).This is another easy tool to see if your interface is actually loading correctly.
Example
#ifconfig
eth0 Link encap:Ethernet HWaddr 00:0A:E6:C6:07:85
inet addr:132.18.0.16 Bcast:132.18.0.255 Mask:255.255.255.0
inet6 addr: fe80::20a:e6ff:fec6:785/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:18458 errors:0 dropped:0 overruns:0 frame:0
TX packets:8982 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:4015093 (3.8 MiB) TX bytes:1449812 (1.3 MiB)
Interrupt:10 Base address:0xd400
Route
This is very useful to check routing config
Example
route -n
Netstat
If you want to see Routing Tables,all open ports,all listen ports
netstat -nr
-n means return numeric output (ie, IP address instead of hostname)
-r means print the routing table
find all open ports
netstat -a
find listening ports
netstat -l
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