IP Addressing and Subnetting
| IP addresses are four 8-bit(1 byte) octets that make up a 32-bit address. These addresses are usually shown in a dotted-decimal form, as in 10.1.2.25. These addresses are sometimes shown as hexadecimal or binary addresses as well. But for this exam you will need to be familiar with these addresses in dotted -decimal form. This hierarchical addressing scheme allows for about 4.3 billion addresses. IP addresses use a hierarchical addressing scheme that is structured by network and host. In larger networks it is structured by network, subnet, and host. Every device on the same network shares the same network address but a unique host address. In the sample address 207.212.78.106, the network address is 207.212.78 and the device's unique node address is 106. Classes of networks are created based on different network sizes. Three classes, Classes A, B, and C, are used to address network nodes in today's networks using TCP/IP. Two other classes also exist; Class D is used for Multicast and Class E addresses are used for research and development of the IP protocol and associated applications. Class A network addresses use only the first octet to assign the network address; the first octet will contain a number between 1 and 126. The three remaining octets are used for the node addressing. Addresses are displayed as network.node.node.node. The address 10.1.1.1 would be an example of a Class A IP address.
A Class B network uses the first two octets to assign the network address. The other two octets are used for node addresses. The format of a Class B address is network.network.node.node. The first octet of a Class B address contains a number between 128 through 191; the second octet contains a number between 0 and 255. Some implementations of TCP/IP allow for the use of zero and 255 in the second octet. The IP address 175.1.1.1 is an example of a Class B IP address. A Class C network address uses the first three octets to identify the network. The first octet contains a value between 192 and 224. The second and third octets can contain any value from 0 to 255. The format of a Class C address is network.network.network.node. An example of a Class C address would be 195.1.1.1. There has been some disagreement that using 255 or zero is not allowed on the Internet. However, as I point out to my students, if you try pinging the real IP addresses of 207.212.0.1 or 207.212.255.1, both get a reply from valid hosts on the Internet as shown in the output below as an address from pacbell.net: C:\> tracert 207.212.255.1 Tracing route to 207-212-255-1.ded.pacbell.net [207.212.255.1] The output above shows an example of using Trace Route, an ICMP utility, to verify the route to the IP address of 207.212.255.1. Subnetting IPYou should have covered subnetting thoroughly in your CCNA book or class. Many mistakes made in networks today involve incorrect subnetting. Why? Because subnetting requires mathematical accuracy.
Subnet MasksEvery machine on the network must be configured with a minimum of an IP address, a default gateway, and a subnet mask to be able to route data between networks. Subnet masks allow network devices using IP addresses to know which part of the IP address will be used as the network address and which part is used for the host address. Table 4.1 shows the default subnet masks for Classes A, B, and C. Table 4.1. The Default Subnet Mask for Class A, B, and C Networks
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EAN: 2147483647
Pages: 213
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