When IPv6 is enabled certain traffic on your Linux server may become slow, that's because in many cases the traffic goes through the IPV6 instead of the IPV4, there is a way to enforce the traffic to go through IPv4.


Simply run the following command in the linux shell:

echo -e "\n#prefer IPv4 over IPv6\nprecedence ::ffff:0:0/96  100" >> /etc/gai.conf

This will basically add the line "precedence ::ffff:0:0/96  100" to the file /etc/gai.conf, this should do. 

Now you should see an improvement in speed as the traffic will go via the IPv4 instead of IPv6.