Impotant Port Numbers

To configure network services/servers, administrator must have a Knowledge of  Port numbers,. So you can  easily find out whether service/daemon is running or not. It will be very helpful when you are configuring iptables/firewall. Ex: You can block unwanted port numbers, it will reduce the risk of hack to the servers.
Here i am listing very common ports which we will use in everyday tasks.


Services                             Portnumber
FTP                                      20 and 21
SSH                                     22
TELNET                               23
SMTP                                  25
DNS                                    53
DHCP                                  67 and 68
TFTP                                   69
HTTP                                   80
NTP                                    123
POP3                                  110
IMAP                                  143
HTTPS                                443
IMAPS                                993
POP3S                                995
SWAT                                 901
SQUID                                3128
MYSQL                              3306
X-WINDOW                        6000
WEBMIN                           10000