II – Maintaining the Servers
1. What is IP Address
IP address is short for Internet Protocol (IP) address.
An IP address is an identifier for a computer or device on a TCP/IP network. Networks using the TCP/IP protocol route messages based on the IP address of the destination.
The Format of an IP Address
The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example, 126.96.36.199 could be an IP address.
Within an isolated network, you can assign IP addresses at random as long as each one is unique. However, connecting a private network to the Internet requires using registered IP addresses (called Internet addresses) to avoid duplicates.
An IP address can be static or dynamic. A static IP address will never change and it is a permanent Internet address. A dynamic IP address is a temporary address that is assigned each time a computer or device accesses the Internet.
Editor’s recommendation: Understanding IP Addressing.
The four numbers in an IP address are used in different ways to identify a particular network and a host on that network. Four regional Internet registries — ARIN, RIPE NCC, LACNIC and APNIC– assign Internet addresses from the following three classes:
Class A – supports 16 million hosts on each of 126 networks
Class B – supports 65,000 hosts on each of 16,000 networks
Class C – supports 254 hosts on each of 2 million networks
The number of unassigned Internet addresses is running out, so a new classless scheme called CIDR is gradually replacing the system based on classes A, B, and C and is tied to adoption of IPv6. In IPv6 the IP address size is increased from 32 bits to 128 bits.
What is My IP Address?
To view your IP address you can use the ipconfig (IPCONFIG) command line tool. Ipconfig displays all current TCP/IP network configuration values and refreshes Dynamic Host Configuration Protocol (DHCP) and Domain Name System (DNS) settings.
To launch the command prompt from a Windows-based computer click: Start > All Programs > Accessories > Command Prompt. Type ipconfig and hit enter.
You can also use Google search to find your IP address. Type what is my IP address as a search query and Google will show the IP address of the computer from which the query was received as the top search result.
Domain names are used to identify one or more IP addresses. For example, the domain name microsoft.com represents about a dozen IP addresses. Domain names are used in URLs to identify particular Web pages. For example, in the URL http:/http://nycitech.com, the domain name is pcwebopedia.com.
Every domain name has a suffix that indicates which top level domain (TLD) it belongs to. There are only a limited number of such domains. For example:
gov – Government agencies
edu – Educational institutions
org – Organizations (nonprofit)
mil – Military
com – commercial business
net – Network organizations
ca – Canada
th – Thailand
Because the Internet is based on IP addresses, not domain names, every Web server requires a Domain Name System (DNS) server to translate domain names into IP addresses.
3. SQL Injection
A form of attack on a database-driven Web site in which the attacker executes unauthorized SQL commands by taking advantage of insecure code on a system connected to the Internet, bypassing the firewall. SQL injection attacks are used to steal information from a database from which the data would normally not be available and/or to gain access to an organization’s host computers through the computer that is hosting the database. SQL injection attacks typically are easy to avoid by ensuring that a system has strong input validation.