Web Servers

IP Addresses

• Every computer on the World Wide Web (a part of the Internet) is connected (indirectly) to every other computer.
• Any computer can specify the "address" any other computer.
• Each computer has a unique "address".
• A computer at a particular "address" can provide a number of different "services". Web serving (the HTTP protocal) is one of these services.
• To find your IP address on a Unix system, use the netstat -r command.

  [killbill@reepicheep perlcgiclass]$ netstat -r
  Kernel IP routing table
  Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
  129.202.180.2   *               255.255.255.255 UH        0 0          0 eth0
  129.202.0.0     *               255.255.0.0     U         0 0          0 eth0
  127.0.0.0       *               255.0.0.0       U         0 0          0 lo
  [killbill@reepicheep perlcgiclass]$ 
  

• The first four number string shown above (129.202.280.2) is a sample unique address.
• To determine the "services" running on a unix system, look at the "/etc/services" file. To find just the www services, use the grep command to filter this file for just the relevant contents.

  [killbill@reepicheep perlcgiclass]$ grep www /etc/services
  www		80/tcp		http		# WorldWideWeb HTTP
  www		80/udp				# HyperText Transfer Protocol
  [killbill@reepicheep perlcgiclass]$ 
  

• This tells us that the www "service" is running on socket number 80 (this is the normal www server socket).