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:
• Network address or ID
• 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:
• www.xxx.yyy.zzz: This notation is indicates that up to three digits can be used for each placing.
• w.x.y.z: This notation is usually utilized to represent an octet that has a value of 0.
• 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:

• Addresses of DNS servers and WINS servers
• Gateway addresses
• TCP/IP configuration parameters.

• Manually assigning IP addresses: IP addressing normally occurs manually under the following conditions:

• When there are no configured DHCP servers on the network and the network haves multiple network segments.
• When you are configuring a computer as a DHCP server, you assign that computer a static IP addresses.
• 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.

Understanding the Hierarchical IP Addressing Structure

As mentioned earlier, IP addresses are 32-bit unique identifiers. The bits of an IP address are divided into octets. The notations used to indicate IP addresses are:

• Dotted-decimal notation
• Binary notation
• Hexadecimal notation

The 32-bit IP address is a hierarchical structured address. IP addresses are not flat addresses. IP addresses are considered hierarchical addresses because the address space is divided into ordered chunks. The 32 bits are not in its entirety a unique identifier. A segment of the IP address is the network address, and another segment is the host (node) address. This segregation is what makes IP addresses hierarchical structured addresses.

• The network address or network ID uniquely identifies a network. All computers and all other devices on the same network, have the identical network address as a segment of their IP address. When using network addresses or IDs, remember the following important rules:

• Because 127 is reserved for loopback addresses, a network address cannot have 127 as the first octet.
• All bits of the network ID cannot be set to ones (1s). This is used for broadcast addresses.
• All bits of the network ID cannot be set to zeroes (0s). This is used to designate the local host.
• If you have different network segments, each network address has to be unique to the IP address.

• Each TCP/IP host on the network, such as a server, router or workstation has a uniquely assigned host address (Host ID), or node address. The host address has to be unique so that each machine on the network can be uniquely identified. When using host addresses or host IDs, remember the following important rules:

• You cannot set all the bits in the host address to all 1s, or to all 0s.
• A host ID has to be unique in the network that it belongs to.

When the Internet was designed, it was decided to create classes of networks. These classes of networks are based on the size of the network.

• Class A network: The Class A network was designed for a very small number of networks which have a large number of nodes or hosts.
• Class B network: The Class B network was designed for networks between very small and very large.
• Class C network: The Class C network was designed for a very large number of networks that have a small number of nodes or hosts.

The characteristics of the network address classes are listed below:

• Class A network:

• Leading bit pattern: 0

Decimal Range of first byte of the network address: 1 – 126

• Maximum number of networks: 126

Maximum nodes per network: 16,777,214

• Class B network:

• Leading bit pattern: 10
• Decimal Range of first byte of the network address: 128 –191
• Maximum number of networks: 16,384
• Maximum nodes per network: 65,534

• Class C network:

• Leading bit pattern: 110
• Decimal Range of first byte of the network address: 192 –223
• Maximum number of networks: 2,097,152
• Maximum nodes per network: 254

Understanding Reserved IP addresses
A few IP addresses are reserved for specific special purposes. The reserved IP addresses are:

• Network segment of the address specified to zeros/0s: Indicates this network or subnet (local network).
• Network segment of the address specified to ones/1s: Indicates this network and all associated subnets.
• Network address 127: The address is reserved for loopback testing.
• Host address of all zeros/0s: The address is typically used in routing tables, and when referencing a network, but not particular hosts on the network.
• Host address of all ones/1s: This is used as a broadcast address for all the nodes on a particular network.
• Full IP address specified as specified as zeros/0s: The address is used by the RIP protocol to specify the default route.
• Full IP address specified as specified as ones/1s: The address is use to broadcast to all nodes on the current network.
Converting Between the Binary Notation and Decimal Notation

In the dotted-decimal notation, the digits 0 to 9 are used. With the 32-bit IP addresses, the octets and bit places are numbered from the left to the right. Each number in the decimal system can be represented in the binary format. The binary system uses only two digits, which are 0 and 1. A binary digit is called a bit. With IP addressing, an octet is formed by 8 bits. An IP address consists of 32 bits, or four octets.

The initial octet refers to the leftmost octet. The bit places 1 to 8 signify the eight leftmost bit places. The second octet signifies the following eight bits, which is bit places 9 to16. The third octet signifies the following eight bits, which is bit places 17 to 24. The fourth octet signifies the following eight bits, which is bit places 25 to 32

• In the dotted-decimal notation, periods are used to divide the four octets.
• In the binary notation, spaces are used to separate the four octets.

If you want to convert a binary number to a decimal number, add the value of each bit position set to 1. If you want to convert a decimal number to a binary number, determine the largest binary bit represented.

Understanding the Different IP Address Classes

• Class A addresses were created for tremendously large networks with many hosts. With Class A addresses, the first high-order bit is zero.

The Class A address format is defined below:

• Network.Node.Node.Node.

The Class A addresses has the following characteristics:

• The first 8 bits or octet is the network address.
• The second octet, third octet and fourth octet defines the host address or ID.
• The maximum number of Class A networks that can be created is 128, of which only 126 is considered possible useable network addresses. This is due to 127 being defined for loopback testing. In addition to this, all bits of the network ID cannot be set to ones (1s) nor can all bits of the network ID be set to zeroes (0s).
• There is also a multitude of useable unique host addresses for a Class A network. The precise figure of possible host addresses is 16,777,216. Of this figure, two addresses are considered reserved IP addresses.

• Class B addresses were created for networks that are medium of size and which have an average number of hosts. With a Class B address, the initial two high-order bits are set to 10.

• • Network.Network.Node.Node.

The Class B address format is defined below:

The Class B addresses have the following characteristics:

• The first 2 octets define the network address.
• A Class B network has more network IDs than a Class A network
• A Class B network has fewer host IDs than a Class A network
• The third octet and fourth octet defines the host address or ID.
• The maximum number of Class B networks that can be created is 16,384.
• Each Class B network can have 65,534 possible host addresses or IDs

• Class C addresses were created for networks that are small and that have few hosts. With a Class C address, the initial three high-order bits are set to 110.

The Class C address format is defined below:

• Network.Network.Network.Node.

The Class C addresses have the following characteristics:

• The first 3 octets define the network address
• The fourth octet defines the host address or ID.
• The maximum number of Class C networks that can be created is 2,097,152.
• Each Class C network can have 254 possible host addresses or IDs

• Class D addresses are reserved for multicasting only. The initial four high-order bits are set to 1110, and the last 28 bits are used for multicast addresses. Multicast Backbone on the Internet (MBONE) uses Class D addresses. MBONE is an extension to the Internet that enables a packet to have more than one destination. The Class D addresses utilize the address range 224.0.0.0 through to 239.255.255.255.
• Class E addresses are reserved for future use, and not supported in Windows Server 2003. The initial five high-order bits are set to 11110. The Class E addresses use the address range 240.0.0.0 to 255.255.255.255.