Defining IP Addresses - Networking Stuffs

[ganeshbala]

Defining IP Addresses

The TCP/IP protocol suite is the more frequently implemented protocol suite in networks today. However, setting up the TCP/IP protocol is not as simple as using one of the other protocol stacks. One of the main requirements of TCP/IP is that each TCP/IP computer has a unique IP address, and other TCP/IP configuration parameters. An IP address can be defined as a unique numeric identifier (address) that is assigned to each computer operating in a TCP/IP based network. IP addresses are considered software addresses, and are not hard coded hardware addresses.

To communicate on the Internet and private TCP/IP network, all hosts defined on the network must have IP addresses. These 32-bit IP address identifies a particular host on the network. While planning for the implementation of a TCP/IP based network, administrators have to clarify what types of IP addresses will be used.

To uniquely identify computers on a TCP/IP network, each computer must have a unique IP address. When a computer running in a TCP/IP network forwards data packets, the packet contains the following IP addresses:

    * The IP address of the computer sending the packet
    * The IP address of the destination computer intended to receive the packet.

The routers use the IP address information to forward the packet to the destination computer. The IP addresses of computers therefore have to be both unique and correct so that they can be forwarded to the correct destination.

IP addresses are categorized into the following categories:

    * Private Addresses: These are addresses that are used on the private network, and which are not visible on the Internet.
    * Public Addresses: These are Internet Assigned Numbers Authority (IANA) registered addresses which are visible on the Internet

IP addresses have the following characteristics:

    * An IP address has 32 bits.
    * An IP address is either a private address or a public address.
    * An IP addresses includes the following components:
          o Network address or ID
          o Host address or ID.
    * IP addresses are expressed in four sets of three numbers, separated with dots.
    * The numbers that exist between each dot is called an octet. This is because when the numbers are converted to binary, it denotes eight binary digits or bits.
    * The bits that make up the IP address can be represented as either of the following notations:
          o www.xxx.yyy.zzz: This notation is indicates that up to three digits can be used for each placing.
          o w.x.y.z: This notation is usually utilized to represent an octet that has a value of 0.

      The above representation is the dotted decimal notation
    * When an octet has a value of less than three digits, it is represented with no leading zeroes.

Understanding Private IP Addresses and Public IP Addresses

Public IP addresses are IP addresses that are connected to the public Internet. To ensure that these IP addresses are unique, the Internet Assigned Numbers Authority (IANA) divides up the non-reserved portion of the IP address space. It then delegates responsibility for public IP address allocation to registries such as the American Registry for Internet Numbers (ARIN) and Asia-Pacific Network Information Center (APNIC). The registries are responsible for allocating blocks of addresses to large InternetS Providers (ISPs). ISPs allocate smaller blocks of addresses to small Internet Service Providers (ISPs) and customers. What normally occurs is that the ISP allocates one public IP address to each computer which is connected to the particular ISP. The particular public IP addresses can be assigned dynamically to each computer when it connects to the ISP, or the IP address can be reserved statically for a dedicated line or a particular dial-up account.

Only those addresses that the IANA has registered are visible on the Internet. IANA functions as the registrar of public IP addresses in order to prevent the duplication of these addresses. The addresses obtained from IANA are simply network identifiers. Administrators then have to assign unique host identifiers (IDs) to each computer and network device. To calculate the IP addresses for computers, you have to combine the network ID assigned by IANA with a unique host ID.

While you can assign public IP addresses to each network device, you should consider the following disadvantages of implementing this strategy:

    * You would deplete the pool of available IP addresses if you assign public IP address to each of your network devices.
    * The private network is vulnerable when public IP addresses are used on the private network. Systems that have a public IP address on the Internet would be able to access your private network. Your devices would also be able to access systems on the Internet.

Private IP addresses are IP addresses that are used on the private network. These addresses are not visible on the public Internet. Private addresses are typically used on TCP/IP networks for servers and workstations accessed by your internal network users. The Internet Assigned Numbers Authority (IANA) has specifically reserved IP addresses which are used for computers on the private network that need to access the Internet. A number of methods can be used to assign private addresses to computers so that they can access the Internet, but are not visible on the Internet.

In RFC 1918 / Address Allocation for Private Internets; IANA has reserved the following three private IP address ranges for private network utilization.

    * 10.0.0.0 to 10.25.255.255
    * 172.16.0.0 to 172.31.255.255
    * 192.168.0.0 to 192.168.255.255

Hosts that have a private IP address can use one of the following methods to access the Internet:

    * A Windows Server 2003 computer set up as a Network Address Translation (NAT) server. Included in Windows Server 2003 is the new Internet Connection Sharing (ICS) feature which offers simpler NAT services to clients on the private network.
    * A proxy server.

IP Address Assignment Methods

IP addressing can occur through either of the following methods:

    * Dynamically assigning IP addresses through Dynamic Host Configuration Protocol (DHCP): You can configure a computer as a DHCP server so that the DHCP server can automatically assign IP addresses to DHCP clients. IP addresses that are assigned via a DHCP server are regarded as dynamically assigned IP addresses. The DHCP server assigns IP addresses from a predetermined IP address range(s). You can set up the DHCP server to assign clients automatically with a number of options, such as:
          o Addresses of DNS servers and WINS servers
          o Gateway addresses
          o TCP/IP configuration parameters.
    * Manually assigning IP addresses: IP addressing normally occurs manually under the following conditions:
          o When there are no configured DHCP servers on the network and the network haves multiple network segments.
          o When you are configuring a computer as a DHCP server, you assign that computer a static IP addresses.
          o When you configure computers as important network servers such as domain controllers, or DNS servers; you manually assign the IP address to these computers.

      Manually assigning IP addresses can be time consuming, and can lead to duplicated IP address assignments. You should only choose to utilize the manual IP addressing method when you cannot use DHCP to automatically assign IP addresses.
    * Automatically assigning IP addresses through Automatic Private IP Addressing (APIPA): APIPA can be used as an alternative when no DHCP server exits to dynamically assign IP address. APIPA works well in smaller networks, when a computer is used on more than one network.