Get information about your network connection with Linux.

Posted: June 15, 2015. At: 2:21 PM. This was 2 years ago. Post ID: 8080
Page permalink: http://securitronlinux.com/bejiitaswrath/get-information-about-your-network-connection-with-linux/

This command will return only the IP address of the host.

ubuntu ~ $ hostname -i
172.31.20.16

Querying for all local IP addresses on the host.

ubuntu ~ $ hostname -I
172.31.20.16 10.8.0.1

This simple script will ping Google and will check the return value of the ping command to see if the Internet is up or not.

ping -c 1 google.com
if [ "$?" == "0" ]; then;
echo "Hi."
else
echo "The Internet is down."
fi

This is yet another way to get IP address information from the host.

ubuntu ~ $ ip a | grep inet
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
    inet 172.31.20.16/20 brd 172.31.31.255 scope global eth0
    inet6 fe80::4d6:3aff:fea8:8213/64 scope link
    inet 10.8.0.1 peer 10.8.0.2/32 scope global tun1194

Use the iptables-save command to dump your iptables rules.

ubuntu ~ $ sudo iptables-save
# Generated by iptables-save v1.4.21 on Mon Jun 15 03:38:37 2015
*nat
:PREROUTING ACCEPT [2326038:117167934]
:INPUT ACCEPT [2144060:106680741]
:OUTPUT ACCEPT [74650:5494320]
:POSTROUTING ACCEPT [74629:5493133]
-A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE
-A POSTROUTING -s 10.8.0.0/24 -j SNAT --to-source 54.66.223.254
COMMIT
# Completed on Mon Jun 15 03:38:37 2015
# Generated by iptables-save v1.4.21 on Mon Jun 15 03:38:37 2015
*filter
:INPUT ACCEPT [17240345:7240229224]
:FORWARD ACCEPT [16635611:20391694822]
:OUTPUT ACCEPT [19729123:22439838587]
COMMIT
# Completed on Mon Jun 15 03:38:37 2015

The nslookup command is used to retrieve DNS information about a certain host. This returns the DNS servers that service that website/host.

ubuntu ~ $ nslookup facebook.com
Server:         172.31.0.2
Address:        172.31.0.2#53
 
Non-authoritative answer:
Name:   facebook.com
Address: 173.252.120.6

Use netstat to list all Internet connections from your machine. Here I am listing all of the listening connections on my cloud instance.

ubuntu ~ $ netstat -l
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 localhost:mysql         *:*                     LISTEN
tcp        0      0 *:ssh                   *:*                     LISTEN
tcp        0      0 *:https                 *:*                     LISTEN
tcp6       0      0 [::]:ssh                [::]:*                  LISTEN
udp        0      0 *:bootpc                *:*
udp        0      0 *:10995                 *:*
udp        0      0 *:2302                  *:*
udp        0      0 *:2303                  *:*
udp        0      0 *:2304                  *:*
udp        0      0 *:2305                  *:*
udp6       0      0 [::]:13242              [::]:*
Active UNIX domain sockets (only servers)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  2      [ ACC ]     SEQPACKET  LISTENING     1171791  /run/udev/control
unix  2      [ ACC ]     STREAM     LISTENING     73100    @/com/ubuntu/upstart
unix  2      [ ACC ]     STREAM     LISTENING     8809     /var/run/dbus/system_bus_socket
unix  2      [ ACC ]     STREAM     LISTENING     9104     /var/run/acpid.socket
unix  2      [ ACC ]     STREAM     LISTENING     640253   /var/run/mysqld/mysqld.sock

To get more DNS information about a host, use the host command like this.

ubuntu ~ $ host -a yahoo.com
Trying "yahoo.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50687
;; flags: qr rd ra; QUERY: 1, ANSWER: 12, AUTHORITY: 0, ADDITIONAL: 0
 
;; QUESTION SECTION:
;yahoo.com.                     IN      ANY
 
;; ANSWER SECTION:
yahoo.com.              3600    IN      NS      ns1.yahoo.com.
yahoo.com.              3600    IN      NS      ns2.yahoo.com.
yahoo.com.              3600    IN      NS      ns3.yahoo.com.
yahoo.com.              3600    IN      NS      ns4.yahoo.com.
yahoo.com.              3600    IN      NS      ns5.yahoo.com.
yahoo.com.              3600    IN      NS      ns6.yahoo.com.
yahoo.com.              87      IN      MX      1 mta6.am0.yahoodns.net.
yahoo.com.              87      IN      MX      1 mta7.am0.yahoodns.net.
yahoo.com.              87      IN      MX      1 mta5.am0.yahoodns.net.
yahoo.com.              256     IN      A       206.190.36.45
yahoo.com.              256     IN      A       98.138.253.109
yahoo.com.              256     IN      A       98.139.183.24
 
Received 262 bytes from 172.31.0.2#53 in 80 ms

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