Linux Tutorials
About Lesson

Port:

One of the most important things is to close all unneeded network ports and know which ports you leave open. Just because anyone can use the port as a door to enter inside your computer and hack your personal information. So you need to care about it and ensure about is there any unneeded or unnecessary port open.

To get the list of open ports run:

netstat –tulpn 

The output of this command will return something like this:

Active Internet connections (only servers)

Proto Recv-Q Send-Q Local Address               Foreign Address                           State                   PID/Program name

tcp        0 0 0.0.0.0:111                 0.0.0.0:*                       LISTEN                 2391/portmap
tcp        0 0 0.0.0.0:22                  0.0.0.0:*                        LISTEN                 1966/sshd
udp        0 0 0.0.0.0:68                  0.0.0.0:*                                                   1570/dhclient
udp        0 0 0.0.0.0:111                 0.0.0.0:*                                                 2391/portmap

 

Services/ports that you may not want to leave running/open are:

Tool/Services   Port Dependencies Handle service
Sendmail 25   SMTP protocol If you need the server to act as SMTP server for outgoing emails only then go to “Secure Sendmail” Section in this document. If you don’t need to use this server as SMTP server
Tool/Services Port Dependencies Handle service
      in any way you can stop it by running:  service sendmail stop chkconfig sendmail off
Portmap (RPC) 111

Handles RPC calls

Used by NFS client

service portmap stop chkconfig portmap off
Nfslock

TCP:32700

UDP:32768,

729

Used by NFS client service nfslock stop chkconfig nfslock off
Cupsd 631 Printing service service cups stop chkconfig cups off
Hplip/hpiod 2208 HP Linux Imaging and Printing service hplip stop chkconfig hplip off
avahi-daemon

UDP:1024 ,

5353, 1025

MDNS/DNS-SD

Multicast DNS service

Discovery

service avahi-daemon stop chkconfig avahi-daemon off

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