====== Disable IPv6 on Ubuntu ======
===== Method 1: sysctl =====
<code>sudo gedit /etc/sysctl.conf</code>

Append to end of file
<code>
# IPv6 disabled
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
</code>

Save the file and close it. Restart sysctl with
<code>sudo sysctl -p</code>
Run
<code>After that run $ cat /proc/sys/net/ipv6/conf/all/disable_ipv6</code>
If it reports ‘1′ means you have disabled IPV6.

or

Check the output of ifconfig again and there should be no ipv6 address
<code>
ifconfig
eth0      Link encap:Ethernet  HWaddr 08:00:27:5f:28:8b  
          inet addr:192.168.1.3  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1346 errors:0 dropped:0 overruns:0 frame:0
          TX packets:965 errors:0 dropped:0 overruns:0 carrier:0
.....
</code>
If it does not work, then try rebooting the system and check ifconfig again.

===== Method 2: grub =====
<code>sudo gedit /etc/default/grub</code>
Look for the line containing "GRUB_CMDLINE_LINUX" and edit it as follows
<code>GRUB_CMDLINE_LINUX="ipv6.disable=1"</code>
The same can also be added to the value of the variable named "GRUB_CMDLINE_LINUX_DEFAULT" and either would work. Save the file, close it and regenerate the grub configuration
<code>sudo update-grub2</code>
Reboot. Now ipv6 should be disabled.