Network Configuration and Troubleshooting Commands

The PCs and devices which are a part of the network can “talk” to one another and exchange data. In addition the PCs and gadgets which are connected, different devices are frequently required for the system to work properly. A Local Area Network (LAN) interfaces PCs which are near one another. Building a LAN is simpler than connecting different neto (to what is called Wide Area Network). The biggest inter network is known as the Internet.

PCs are joined in a network to exchange information or resources one another. Two or more PC connected through network media called computer network. To set a system suitable media is needed. This can be wired or remote. Twisted-pair, co-axial or fiber-optic are samples of link and infra-red, blue-tooth, radio-wave, micro-wave and so on are remote media utilized for networking. When you are working with an insignificant LAN, PCs, media and peripherals are sufficient. In any case, when you are working with a wider range you have utilize some extra devices like bridge, gateway or route to interface different small or large networks.

ifconfig

ifconfig remains for “interface configuration”. It is utilized to view and change the configuration of the network interfaces on your system. With this command you can see IP Address and Hardware/ MAC address assign to interface further more MTU (Maximum transmission unit) size.

# ipconfig

Output:

eth0      Link encap:Ethernet  HWaddr 36:1D:6E:FF:B4:07
          inet addr:192.168.10.43  Bcast:192.168.10.255  Mask:255.255.255.0
          inet6 addr: fe80::341d:6eff:feff:b407/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:26366 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6919 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:13934364 (13.2 MiB)  TX bytes:449359 (438.8 KiB)
          Interrupt:20

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:65536  Metric:1
          RX packets:1101 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1101 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:96888 (94.6 KiB)  TX bytes:96888 (94.6 KiB)

In any case, to show information of a particular system interface like eth0 , simply type:

# ipconfig eth0

Output:

eth0      Link encap:Ethernet  HWaddr 36:1D:6E:FF:B4:07
          inet addr:192.168.10.43  Bcast:192.168.10.255  Mask:255.255.255.0
          inet6 addr: fe80::341d:6eff:feff:b407/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:26366 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6919 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:13934364 (13.2 MiB)  TX bytes:449359 (438.8 KiB)
          Interrupt:20

Configure an Interface
These configurations can consolidated in a single command. Case in point, to configure interface eth0 to use the static IP address, netmask and broadcast address, then use the following command:

# ifconfig eth0 192.168.10.48 netmask 255.255.255.0 broadcast 192.168.10.2

Assign only a static IP address to an interface, specify the interface name and the IP address.

# ifconfig eth0 192.168.10.48

To assign a network mask to an interface, use the keyword netmask and the netmask address.

# ifconfig etho netmask 255.255.255.0

To assign a broadcast address to an interface, use the keyword broadcast and the broadcast address.

# ifconfig etho broadcast 192.168.10.3

Enable or Disable Interface
You can use ifconfig to change the status of a network interface from inactive to active, or vice-versa. To enable an inactive interface use up keywork and to disable an active interface use down keyword.
Enable the inactive interface:

# ifconfig eth0 up

Disable the active interface:

# ifconfig eth1 down

Setting MTU Size
By default MTU size is 1500. Sets the maximum IP packet size for this system. The Value variable can be any number from 60 through 4096, depending upon the network interface.

# ifconfig eth0 mtu value

Example:

# ifconfig eth0 mtu 3000

PING Command

PING (Packet INternet Groper) command is the best way to test connectivity between two nodes. Ping is a basic approach to send network information to, and get system information from another PC on a network. It is as often as possible used to test, at the most basic level, whether another system is reachable over a network, and if so, how much time it takes for that data to be exchanged.

# ping 8.8.8.4

Output:

PING 8.8.4.4 (8.8.4.4) 56(84) bytes of data.
64 bytes from 8.8.4.4: icmp_seq=1 ttl=44 time=84.2 ms
64 bytes from 8.8.4.4: icmp_seq=2 ttl=44 time=81.0 ms
64 bytes from 8.8.4.4: icmp_seq=3 ttl=44 time=80.3 ms
64 bytes from 8.8.4.4: icmp_seq=4 ttl=44 time=80.7 ms

You can also ping domain name also.

# ping www.techoism.com

Output:

PING www.techoism.com (67.225.171.8) 56(84) bytes of data.
64 bytes from svr154.fastwebhost.com (67.225.171.8): icmp_seq=1 ttl=49 time=231 ms
64 bytes from svr154.fastwebhost.com (67.225.171.8): icmp_seq=2 ttl=49 time=231 ms
64 bytes from svr154.fastwebhost.com (67.225.171.8): icmp_seq=3 ttl=49 time=231 ms
64 bytes from svr154.fastwebhost.com (67.225.171.8): icmp_seq=4 ttl=49 time=230 ms

In Linux ping command keep executing until you interrupt. Ping with -c option exit after N number of request.

# ping -c 3 www.techoism.com

Output:

PING www.techoism.com (67.225.171.8) 56(84) bytes of data.
64 bytes from svr154.fastwebhost.com (67.225.171.8): icmp_seq=1 ttl=49 time=231 ms
64 bytes from svr154.fastwebhost.com (67.225.171.8): icmp_seq=2 ttl=49 time=231 ms
64 bytes from svr154.fastwebhost.com (67.225.171.8): icmp_seq=3 ttl=49 time=231 ms

--- www.techoism.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2231ms
rtt min/avg/max/mdev = 231.117/231.214/231.407/0.571 ms

TRACEROUTE Command

The Internet is an large and complex collection of network hardware, connected together by gateways. Traceroute command is a network diagnostic tool for showing the route packets take to network host or destination. It indicates how long each hop will takes and what number of hop that the packet requires to reach the specify destination.

# traceroute www.techoism.com

Output:

traceroute to www.techoism.com (67.225.171.8), 30 hops max, 60 byte packets
 1  192.168.10.19 (192.168.10.19)  0.623 ms  0.565 ms  0.548 ms
 2  180.211.97.49 (180.211.97.49)  1.798 ms  1.772 ms  1.745 ms
 3  202.131.102.137 (202.131.102.137)  1.786 ms  1.684 ms  1.728 ms
 4  202.131.101.77 (202.131.101.77)  1.691 ms  1.658 ms  1.617 ms
 5  static-221.65.93.111-tataidc.co.in (111.93.65.221)  2.172 ms  2.931 ms  3.242 ms
 6  121.241.90.69.static-ahmedabad.vsnl.net.in (121.241.90.69)  1.728 ms  2.072 ms  2.241 ms
 7  172.29.211.217 (172.29.211.217)  16.074 ms  16.056 ms  11.534 ms
 8  ix-0-100.tcore1.MLV-Mumbai.as6453.net (180.87.38.5)  42.744 ms  16.038 ms  15.997 ms
 9  if-2-2.tcore2.MLV-Mumbai.as6453.net (180.87.38.2)  205.211 ms  204.846 ms  205.023 ms
10  if-6-2.tcore1.L78-London.as6453.net (80.231.130.5)  195.622 ms  195.577 ms  202.540 ms
11  if-7-2.thar1.NJY-Newark.as6453.net (66.198.70.25)  212.014 ms  203.996 ms if-4-2.thar1.NJY-Newark.as6453.net (80.231.130.34)  200.219 ms
12  if-1-3.thar2.NJY-Newark.as6453.net (216.6.57.2)  207.442 ms  204.905 ms  205.712 ms
13  if-14-14.tcore2.NTO-New-York.as6453.net (66.198.111.126)  203.925 ms  200.535 ms  197.195 ms
14  66.110.96.5 (66.110.96.5)  205.638 ms  203.884 ms  201.640 ms
15  66.110.96.150 (66.110.96.150)  206.403 ms 66.110.96.134 (66.110.96.134)  209.831 ms 66.110.96.146 (66.110.96.146)  204.219 ms
16  he-5-10-0-0-cr01.newyork.ny.ibone.comcast.net (68.86.84.249)  199.922 ms he-5-3-0-0-cr01.newyork.ny.ibone.comcast.net (68.86.83.101)  203.808 ms he-5-10-0-0-cr01.newyork.ny.ibone.comcast.net (68.86.84.249)  209.206 ms
17  be-10206-cr01.350ecermak.il.ibone.comcast.net (68.86.86.226)  228.357 ms  228.326 ms  228.299 ms
18  he-0-12-0-1-pe03.350ecermak.il.ibone.comcast.net (68.86.86.22)  226.148 ms  222.071 ms  223.949 ms
19  50.242.150.126 (50.242.150.126)  220.079 ms * 50.242.150.130 (50.242.150.130)  221.460 ms
20  lw-dc3-core1-te8-16.rtr.liquidweb.com (209.59.157.244)  231.375 ms  234.539 ms  233.977 ms
21  lw-dc3-dist13-po5.rtr.liquidweb.com (69.167.128.73)  230.574 ms  228.013 ms  225.895 ms

NETSTAT Command

netstat (network statistics) is a command line tool for monitoring network connections both incoming and outgoing as well as viewing routing tables, interface statistics etc.

# netstat -r

Output:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.10.0    *               255.255.255.0   U         0 0          0 eth0
link-local      *               255.255.0.0     U         0 0          0 eth0
default         192.168.10.28   0.0.0.0         UG        0 0          0 eth0

DIG Command

Dig remains for “domain information groper”. Dig provide query DNS related information like A Record, CNAME, MX Record etc.

# dig www.techoism.com

Output:

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.30.rc1.el6_6.3 <<>> www.techoism.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11472
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;www.techoism.com.              IN      A

;; ANSWER SECTION:
www.techoism.com.       299     IN      A       67.225.171.8

;; Query time: 119 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Mon Jun 22 17:08:13 2015
;; MSG SIZE  rcvd: 50

NSLOOKUP Command

nslookup, which remains for "name server lookup", is a valuable tool for finding out information about a named domain. By default, nslookup will translate a domain name to an IP address (or vice versa).

# nslookup www.techoism.com

Output:

Server:         8.8.8.8
Address:        8.8.8.8#53

Non-authoritative answer:
Name:   www.techoism.com
Address: 67.225.171.8

ROUTE Command

route command by default will show the details of the kernel routing table entries.

# route

Output:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.10.0    *               255.255.255.0   U     0      0        0 eth0
link-local      *               255.255.0.0     U     1002   0        0 eth0
default         192.168.10.19   0.0.0.0         UG    0      0        0 eth0

HOST Command

host is a simple utility for performing DNS lookups. It is normally used to convert names to IP addresses and vice versa.

# host www.techoism.com

Output:

www.techoism.com has address 67.225.171.8

ARP Command

arp which remains for "Address Resolution Protocol". ARP is useful to view/add the contents of the kernel’s ARP tables.

# arp -e

Output:

Address                  HWtype  HWaddress           Flags Mask            Iface
192.168.10.28            ether   00:1c:f0:98:07:3a   C                     eth0
192.168.10.43            ether   36:1d:6e:ff:b4:07   C                     eth0
192.168.10.57            ether   b8:2a:72:b0:33:1e   C                     eth0

ETHTOOL Command

When you execute ethtool command with a device name, it displays the following information about the ethernet device.

# ethtool eth0

Output:

Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Supported pause frame use: Symmetric
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Advertised pause frame use: Symmetric
        Advertised auto-negotiation: Yes
        Speed: 1000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: on
        MDI-X: off (auto)
        Supports Wake-on: pumbg
        Wake-on: g
        Current message level: 0x00000007 (7)
                               drv probe link
        Link detected: yes

HOSTNAME Command

The hostname command is used to show or set a computer's host name and domain name. It is one of the most basic of the network administrative utilities.

# hostname

Output:

server.techoism.com