Why does nmap produce different results on two machines?

Question

Information Security

Hey! The command executed on two PCs (server and personal / CentOS & Ubuntu respectively) looks something like this:
sudo /usr/bin/nmap -sS -O -oX 92fae394572c8dc250f5eee83c392235e7ceb6e0.xml site.ru
In order to execute it on the server via sudores permission is set for execution. I start scanning and here is the first question! nmap on a personal PC did it in 260.3 seconds.... and on the server 1.8. It seemed strange, but he (the server version) determined the ports, and all the services too! That's just the problem on the server shows that all ports are open, and on a personal one that some of them are filtered. How to fix it? Thank you)
There is an assumption that this is due to different versions, but the package was installed today for both ... on CentOS 6.40, Ubuntu 7.60. Tried to update on CentOS - in vain.

Answer 1

The time differs due to the fact that some of the ports are filtered. Check the firewall settings (most likely on the target machine), filtered - means that the server did not bother to send a response, and firewalls do this, because according to the standard it is mandatory to send a response.

Answer 2

On a personal tyrnet is filtered - that's why it takes so long