tailieunhanh - Internetworking with TCP/IP- P11

Internetworking with TCP/IP- P11: TCP/IP has accommodated change well. The basic technology has survived nearly two decades of exponential growth and the associated increases in traffic. The protocols have worked over new high-speed network technologies, and the design has handled applications that could not be imagined in the original design. Of course, the entire protocol suite has not remained static. New protocols have been deployed, and new techniques have been developed to adapt existing protocols to new network technologies | 68 Classful Internet Addresses Chap. 4 IP Multicast Addresses In addition to unicast delivery in which a packet is delivered to a single computer and broadcast delivery in which a packet is delivered to all computers on a given network the IP addressing scheme supports a special form of multipoint delivery known as multicasting in which a packet is delivered to a specific subset of hosts. IP multicasting is especially useful for networks where the hardware technology supports multicast delivery. Chapter 17 discusses multicast addressing and delivery in detail. For now it is sufficient to understand that Class D addresses are reserved for multicasting. Weaknesses In Internet Addressing Encoding network information in an internet address does have some disadvantages. The most obvious disadvantage is that addresses refer to network connections not to the host computer If a host computer moves from one network to another its IP address must change. To understand the consequences consider a traveler who wishes to disconnect his or her personal computer carry it along on a trip and reconnect it to the Internet after reaching the destination. The personal computer cannot be assigned a permanent IP address because an IP address identifies the network to which the machine attaches. Chapter 19 shows how the IP addressing scheme makes mobility a complex problem. Another weakness of the classful addressing scheme is that when any class C network grows to more than 255 hosts it must have its address changed to a class B address. While this may seem like a minor problem changing network addresses can be incredibly time-consuming and difficult to debug. Because most software is not designed to handle multiple addresses for the same physical network administrators cannot plan a smooth transition in which they introduce new addresses slowly. Instead they must abruptly stop using one network address change the addresses of all machines and then resume communication using .