How to make apache server listen on particular port ?

Apache can be made to listen to a particular port/ip address using Listen directive.

Syntax :
Listen [IP_Address:]Port

Examples :
Listen 0.0.0.0:80
Listen 80
Listen 127.0.0.1:80
Listen 191.20.20.21:8000

• Listen directive tells the server to listen for http request on the specified port or IP address (the number of IP’s for a machine depends upon the number of Network Interface Cards) and port combinations.
• If only port number is specified the server listens to the given port on all Network Interfaces.
• If both IP address and port is given, the server will listen on the given port and interface.
• Multiple Listen directives can be used to specify a number of addresses and ports to listen on.
• The server will respond to requests from any of the listed addresses and ports.

For example, to make the server accept connections on both port 80 and port 8080, on all interfaces, use:

Listen 80
Listen 8080

To make the server accept connections on port 80 for one interface, and port 8080 on another, use

Listen 191.20.20.20:80
Listen 191.20.20.21:8000

Note :

1. The number of IP’s for a machine depends upon the number of Network Interface Cards(NIC). If a machine has 2 NIC’s installed, then it can have 2 IP’s.
2. The IP address 0.0.0.0 means “every IP that the computer provides”.
3. The IP address 127.0.0.1 is computer’s loopback address.
4. Network IP addresses like 127.0.0.1 do not reach outside, but are re-routed by the computer’s own network adapter back to the TCP/IP stack.
5. To get all listening tcp port one can use the command netstat -lntp, l – listening port, n – print numeric IP address, t – list only tcp socket, p – print process ID.