28.1 Introduction to TCPIP

   

---

28.1 Introduction to TCP/IP

The Transmission Control Protocol/Internet Protocol (TCP/IP) is the most widely used network protocol in the world. This is a five-layer protocol where the lower four layers of the protocol stack resemble the OSI model. The application layer in the TCP/IP model provides the same functionality as do the upper three layers in the OSI model. The Internet Protocol (IP) is used in the network layer of this model for host addressing. Each host on a TCP/IP network is known by its IP address, which is a 32-bit number divided into four parts . TCP/IP provides connection-oriented and connection-less data transfer with the help of two protocols (TCP and UDP) in the fourth layer, which will be discussed shortly.

TCP/IP Layers

The physical layer and the data link layer of the TCP/IP model are like any other network protocol stack. These two layers consist of cabling, network interface adapters, and software drivers for these adapters. A comparison of the TCP/IP and OSI models is shown in Figure 28-1.

Figure 28-1. Comparison of TCP/IP and OSI models.

IP Address

Addresses assigned to each host in the IP layer are called IP addresses. Each IP address is a 32-bit number divided into four parts of 8 bits each. Each part consisting of 4 bits is called an octet. Octets in the IP address are separated by dot symbols. Since an octet consists of 8 bits, its value can range from 0 to 255. A typical IP address looks like 192.168.3.45. All nodes on a network must have unique IP addresses.

IP addresses are not assigned randomly , but in an orderly fashion. If you want to connect your local network to the Internet, you have to get legal IP addresses from your network provider to avoid duplication of IP addresses and maintain of proper routing. However, if your network is an isolated one, you can use your own IP address assignment scheme.

It should be clarified at this point that IP addresses are not like MAC addresses that are used at the data link layer. MAC addresses are hardware addresses that are fixed for network interface adapters. IP addresses are logical addresses and are assigned by a network administrator during the configuration process of a network. Another difference is that MAC addresses are 48 bits long whereas IP addresses are 32 bits long.

Network Address

An IP address consists of two parts, a network part and a host part. The network part of the IP address is called a network address. It is common to all hosts on a network, whereas the host part is unique for every system connected to a network. For example, 24 bits starting from the left can be used as the network address, and the remaining 8 bits can be used for host addresses.

Note

Network addresses in an IP-based network are logical addresses. More than one IP network can exist on a single physical network. HP-UX also supports virtual adapters for assigning multiple IP addresses to a single physical network interface adapter.

IP Address Classes

Depending on the number of bits used for the network part of an IP address, IP addresses are divided into classes, each of which is intended for a specific purpose.

• Class A is used for very large networks having more than 65,000 nodes.

• Class B is used for medium- size networks where the number of nodes is less than 65,000 but more than 254.

• Class C is used for small networks with less than 255 nodes.

• Class D is a special class of IP addresses intended for multicast networks.

• Class E is reserved for future use.

CLASS A NETWORKS

Class A networks use the leftmost octet as the network address and the other three octets as the host or node address. All IP addresses that start with a first bit of 0 fall into this category. This is the range of IP addresses with a first octet value ranging from 1 to 127. The maximum number of hosts in a class A network is 2 ²⁴ 2. Figure 28-2 shows the division of class A IP address bits into network and host parts.

Figure 28-2. Division of network and host parts in a class A IP address.

CLASS B NETWORKS

Two octets of an IP address from the left-hand side are used as the network part in class B networks. All IP addresses starting with bit pattern 10 are class B addresses. IP addresses with a first octet value from 128 to 191 fall into class B category. The maximum number of hosts in a class B network is 2 ¹⁶ 2. Figure 28-3 shows the division of class B IP address bits into network and host parts.

Figure 28-3. Division of network and host parts in a class B IP address.

CLASS C NETWORKS

Three octets from the left-hand side in an IP address are used for the network part while the rightmost octet is used for the host part. All IP addresses starting with bit pattern 110 are class C IP addresses. IP addresses with a first octet value from 192 to 223 fall into this category. At the most, 254 hosts can be placed in a class C network. Figure 28-4 shows division of class C IP address bits into network and host parts.

Figure 28-4. Division of network and host parts in a class C IP address.

Table 28-1 summarizes the properties of IP address classes, where the starting bit pattern and number of bits in the host and network parts for each class are shown.

Table 28-1. Summary of IP Address Classes

Class	Starting Bit Pattern	Network Bits	Host Bits
A		8	24
B	10	16	16
C	110	24	8

---

   

Top