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# Connection Oriented Networks - Perros H.G

Perros H.G Connection Oriented Networks - John Wiley & Sons, 2005. - 359 p.
ISBN 0-470-02163-2
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• Padding: A variable-length field used to make the header of the datagram an integral multiple of 32-bit words.
As we saw above, IP addresses are 32 bits long. An IP address is divided into two parts: a network and a suffix. The network identifies the physical network that the host computer is attached to. The suffix identifies the host computer itself. The size of these two fields vary according to the class of the IP address. Specifically, five different classes of addresses - A, B, C, D, and E - have been defined (see Figure 6.2).
0 ...... .......................
Network Suffix

1 0 Network Suffix

1 1 0 Network Suffix

1 1 1 0 Multicast address

1 1 1 1 0 Reserved for future use
A
Figure 6.2 The IP address classes.
134
THE MULTI-PROTOCOL LABEL SWITCHING (MPLS) ARCHITECTURE
Classes A, B and C are called the primary classes because they are used for host addresses. Class D is used for multicasting; class E is reserved for future use. The first field determines the class of the IP address, and it ranges from 1 bit for a class A address to 5 bits for a class E addresses. The second field gives the network address, and the third field is the suffix which gives the host address.
Network addresses are usually written in the dotted decimal notation. That is, each byte is written in decimal, ranging from 0 to 255. As an example, the IP address 00000111 00000010 00000000 00000010 will be written as 7.2.0.2. Using this notation, we have that the range of class A addresses is from 1.0.0.0 to 127.255.255.255, for class B we have a range of values from 128.0.0.0 to 191.255.255.255, and for class C we have a range of 192.0.0.0 to 233.255.255.255.
Class C is very common, whereas class A is rarely used since there are only few networks with that large number of hosts. IP reserves host address 0 to denote the address of a network. For instance, in the class B address 128.32.0.0 the network field is 128.32 and the suffix is 0.0. This indicates the address of the network 128.32. For broadcasting within the network, IP uses the address 128.32.255.255.
IP assigns multiple IP addresses to routers, since a router is attached to multiple networks. Specifically, a router has one IP address for each network that it is attached to. An individual host connected to multiple networks has also multiple IP addresses, one for each network connection. Such a host is referred to as multihomed.
Subnetting