13 Linux Network Configuration and Troubleshooting Commands

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Computers are connected in a network in order to exchange information or resources with one another. Two or more computers are connected through network media called a. connected Computer network. A variety of network devices or media are required to form a computer network.

Computer loaded with Linux operating system can also be part of a network, regardless of whether it is a small or large network Multitasking and multiuser Natures. The maintenance of the system and network operation is a task of the System / network administrators Work.

[ You might also like: 22 Linux Networking Commands for Sysadmin ]

In this article, we’re going to review commonly used network configuration and troubleshooting commands in Linux.

1. ifconfig command

ifconfig (Interface configurator) Command is used to initialize an interface, assign it IP address Interface and enable or deactivate Interface on request.

With this command you can view IP address and hardware / MAC address assign to the interface and also MTU (Maximum transfer unit) Size.

# ifconfig

eth0      Link encap:Ethernet  HWaddr 00:0C:29:28:FD:4C
          inet addr:192.168.50.2  Bcast:192.168.50.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe28:fd4c/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:6093 errors:0 dropped:0 overruns:0 frame:0
          TX packets:4824 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:6125302 (5.8 MiB)  TX bytes:536966 (524.3 KiB)
          Interrupt:18 Base address:0x2000

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:8 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:480 (480.0 b)  TX bytes:480 (480.0 b)

ifconfig with interface (eth0) Command only shows specific interface details like IP address, MAC address, etc. with -a Option shows all available interface details if it is also deactivated.

# ifconfig eth0

eth0      Link encap:Ethernet  HWaddr 00:0C:29:28:FD:4C
          inet addr:192.168.50.2  Bcast:192.168.50.255  Mask:255.255.255.0
          inet6 addr: fe80::20c:29ff:fe28:fd4c/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:6119 errors:0 dropped:0 overruns:0 frame:0
          TX packets:4841 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:6127464 (5.8 MiB)  TX bytes:539648 (527.0 KiB)
          Interrupt:18 Base address:0x2000

Set the IP address and gateway in Linux

Assign one IP address and goal on-the-fly to the interface. The setting is removed when the system is restarted.

# ifconfig eth0 192.168.50.5 netmask 255.255.255.0

Activate or deactivate specific interface

to enable or deactivate For a specific interface we use the example command as follows.

Activate eth0
# ifup eth0
Disable eth0
# ifdown eth0

Setting the MTU size

By default MTU Size is 1500. We can hire the necessary MTU Size with the following command. Substitute XXX with size.

# ifconfig eth0 mtu XXXX

Put the interface in promiscuous mode

The network interface only received packets that belong to this particular one THREAD. If you put the interface in the Promiscuous Mode it receives all packets. This is very useful for capturing packets and analyzing them later. You may need superuser access to do this.

# ifconfig eth0 - promisc

To update: The ifconfig Command is replaced with the IP command in most modern Linux distributions.

2. Ping command

Ring (Internet Groper package) Command is the best way to test connectivity between two knots. Whether it is Local network (LAN) or Wide area network (VAN).

Ping used ICMP (Internet Control Message Protocol) to communicate with other devices. You can ping the hostname or IP address with the following commands.

# ping 4.2.2.2

PING 4.2.2.2 (4.2.2.2) 56(84) bytes of data.
64 bytes from 4.2.2.2: icmp_seq=1 ttl=44 time=203 ms
64 bytes from 4.2.2.2: icmp_seq=2 ttl=44 time=201 ms
64 bytes from 4.2.2.2: icmp_seq=3 ttl=44 time=201 ms

OR

# ping www.tecmint.com

PING tecmint.com (50.116.66.136) 56(84) bytes of data.
64 bytes from 50.116.66.136: icmp_seq=1 ttl=47 time=284 ms
64 bytes from 50.116.66.136: icmp_seq=2 ttl=47 time=287 ms
64 bytes from 50.116.66.136: icmp_seq=3 ttl=47 time=285 ms

in the Linux The ping command will continue to run until you interrupt it. Ping with -c Exit after option n Number of requests (success or failure response).

# ping -c 5 www.tecmint.com

PING tecmint.com (50.116.66.136) 56(84) bytes of data.
64 bytes from 50.116.66.136: icmp_seq=1 ttl=47 time=285 ms
64 bytes from 50.116.66.136: icmp_seq=2 ttl=47 time=285 ms
64 bytes from 50.116.66.136: icmp_seq=3 ttl=47 time=285 ms
64 bytes from 50.116.66.136: icmp_seq=4 ttl=47 time=285 ms
64 bytes from 50.116.66.136: icmp_seq=5 ttl=47 time=285 ms

--- tecmint.com ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4295ms
rtt min/avg/max/mdev = 285.062/285.324/285.406/0.599 ms

3. Traceroute command

Trace route is a network troubleshooting utility that displays the number of hops it will take to reach a destination and also determines the path of the packets. Below we follow the path to global DNS server IP address and being able to reach the destination also shows the path the package is traveling.

# traceroute 4.2.2.2

traceroute to 4.2.2.2 (4.2.2.2), 30 hops max, 60 byte packets
 1  192.168.50.1 (192.168.50.1)  0.217 ms  0.624 ms  0.133 ms
 2  227.18.106.27.mysipl.com (27.106.18.227)  2.343 ms  1.910 ms  1.799 ms
 3  221-231-119-111.mysipl.com (111.119.231.221)  4.334 ms  4.001 ms  5.619 ms
 4  10.0.0.5 (10.0.0.5)  5.386 ms  6.490 ms  6.224 ms
 5  gi0-0-0.dgw1.bom2.pacific.net.in (203.123.129.25)  7.798 ms  7.614 ms  7.378 ms
 6  115.113.165.49.static-mumbai.vsnl.net.in (115.113.165.49)  10.852 ms  5.389 ms  4.322 ms
 7  ix-0-100.tcore1.MLV-Mumbai.as6453.net (180.87.38.5)  5.836 ms  5.590 ms  5.503 ms
 8  if-9-5.tcore1.WYN-Marseille.as6453.net (80.231.217.17)  216.909 ms  198.864 ms  201.737 ms
 9  if-2-2.tcore2.WYN-Marseille.as6453.net (80.231.217.2)  203.305 ms  203.141 ms  202.888 ms
10  if-5-2.tcore1.WV6-Madrid.as6453.net (80.231.200.6)  200.552 ms  202.463 ms  202.222 ms
11  if-8-2.tcore2.SV8-Highbridge.as6453.net (80.231.91.26)  205.446 ms  215.885 ms  202.867 ms
12  if-2-2.tcore1.SV8-Highbridge.as6453.net (80.231.139.2)  202.675 ms  201.540 ms  203.972 ms
13  if-6-2.tcore1.NJY-Newark.as6453.net (80.231.138.18)  203.732 ms  203.496 ms  202.951 ms
14  if-2-2.tcore2.NJY-Newark.as6453.net (66.198.70.2)  203.858 ms  203.373 ms  203.208 ms
15  66.198.111.26 (66.198.111.26)  201.093 ms 63.243.128.25 (63.243.128.25)  206.597 ms 66.198.111.26 (66.198.111.26)  204.178 ms
16  ae9.edge1.NewYork.Level3.net (4.68.62.185)  205.960 ms  205.740 ms  205.487 ms
17  vlan51.ebr1.NewYork2.Level3.net (4.69.138.222)  203.867 ms vlan52.ebr2.NewYork2.Level3.net (4.69.138.254)  202.850 ms vlan51.ebr1.NewYork2.Level3.net (4.69.138.222)  202.351 ms
18  ae-6-6.ebr2.NewYork1.Level3.net (4.69.141.21)  201.771 ms  201.185 ms  201.120 ms
19  ae-81-81.csw3.NewYork1.Level3.net (4.69.134.74)  202.407 ms  201.479 ms ae-92-92.csw4.NewYork1.Level3.net (4.69.148.46)  208.145 ms
20  ae-2-70.edge2.NewYork1.Level3.net (4.69.155.80)  200.572 ms ae-4-90.edge2.NewYork1.Level3.net (4.69.155.208)  200.402 ms ae-1-60.edge2.NewYork1.Level3.net (4.69.155.16)  203.573 ms
21  b.resolvers.Level3.net (4.2.2.2)  199.725 ms  199.190 ms  202.488 ms

4. Netstat command

Netstat (Network statistics) Command displays connection information, routing table information, and so on. To view route table information, use the as option -r.

# netstat -r

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.50.0    *               255.255.255.0   U         0 0          0 eth0
link-local      *               255.255.0.0     U         0 0          0 eth0
default         192.168.50.1    0.0.0.0         UG        0 0          0 eth0

More examples of Netstat command, please see our previous article on 20 examples of Netstat commands on Linux.

To update: The netstat The command is replaced by the ss (socket statistics) command in most modern Linux distributions.

5. Grave order

she (Domain information seeker) Inquiry DNS related information such as A Record, CNAME, MX record, etc. This command is mainly used for troubleshooting DNS-related Interrogate.

# dig www.tecmint.com; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.10.rc1.el6 <<>> www.tecmint.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<

More examples of Excavation order, please read the article on 10 Linux Dig Commands to Query DNS.

6. Nslookup command

nslookup Command is also used to find out DNS-related Interrogate. The following examples show A Record (IP address) from tecmint.com.

# nslookup www.tecmint.com
Server:         4.2.2.2
Address:        4.2.2.2#53

Non-authoritative answer:
www.tecmint.com canonical name = tecmint.com.
Name:   tecmint.com
Address: 50.116.66.136

For more Nslookup command, read the article on 8 examples of Linux nslookup commands.

7. Route command

route Command shows and manipulates the too ip Routing table. This is how you can see the standard routing table in Linux, enter the following command.

# route

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.50.0    *               255.255.255.0   U     0      0        0 eth0
link-local      *               255.255.0.0     U     1002   0        0 eth0
default         192.168.50.1    0.0.0.0         UG    0      0        0 eth0

Add, delete routes and default gateway with the following commands.

Add route on Linux
# route add -net 10.10.10.0/24 gw 192.168.0.1
Delete route under Linux
# route del -net 10.10.10.0/24 gw 192.168.0.1
Add default gateway in Linux
# route add default gw 192.168.0.1

8. Host command

host Command to find a name IP or IP to name IPv4 or IPv6 and also query DNS Records.

# host www.bing.com

www.bing.com has address 173.194.38.180
www.bing.com has address 173.194.38.176
www.bing.com has address 173.194.38.177
www.bing.com has address 173.194.38.178
www.bing.com has address 173.194.38.179
www.bing.com has IPv6 address 2404:6800:4003:802::1014

Using -t an option to discover DNS resource records like CNAME, NS, MX, SOA, Etc.

# host -t CNAME www.redhat.com

www.redhat.com is an alias for wildcard.redhat.com.edgekey.net.

9. Arp command

ARP (Address Resolution Protocol) is useful to view / add the contents of the kernel ARP tables. To view the standard table, use the as command.

# arp -e

Address                  HWtype  HWaddress           Flags Mask            Iface
192.168.50.1             ether   00:50:56:c0:00:08   C                     eth0

10. Ethtool command

ethtool is a substitute for mii-tool. It is used to view, set your speed and duplex network card (THREAD). You can permanently duplex in / etc / sysconfig / network-scripts / ifcfg-eth0 With ETHTOOL_OPTS Variable.

# ethtool eth0

Settings for eth0:
        Current message level: 0x00000007 (7)
        Link detected: yes

11. Iwconfig command

iwconfig Command in Linux is used to a. to configure wireless network interface. You can see and set the basics Wireless Internet access Details like SSID Channel and encryption. You can refer to the man page for. refer iwconfig learn more.

# iwconfig [interface]

12. Hostname command

the Hostname can be identified in a network. Run the Hostname Command to display the host name of your box. You can set the host name permanently in / etc / sysconfig / network. You have to restart the box after setting a correct host name.

# hostname 

tecmint.com

13. Nmcli and Nmtui tools

The Nmcli and Nmtui tools are used to configure network settings and also to manage network devices, create, change, activate / deactivate and delete network connections in Linux systems.

# nmcli
# nmtui
Nmtui network manager

This article can be for everyday use by. to be useful Linux network administrators in Linux / Unix-like operating systems. Please let us know via our comments box if we missed it.