3.11 Summary

3.11 Summary

We started this chapter with a description of the IP header and briefly described all the fields in this header. We also gave an introduction to IP routing, and saw that host routing can be simple: the destination is either on a directly connected network, in which case the datagram is sent directly to the destination, or a default router is chosen .

Hosts and routers have a routing table that is used for all routing decisions. There are three types of routes in the table: host specific, network specific, and optional default routes. There is a priority to the entries in a routing table. A host route will be chosen over a network router, and a default route is used only when no other route exists to the destination.

IP routing is done on a hop-by-hop basis. The destination IP address never changes as the datagram proceeds through all the hops, but the encapsulation and destination link-layer address can change on each hop. Most hosts and many routers use a default next -hop router for all nonlocal traffic.

Class A and B addresses are normally subnetted . The number of bits used for the subnet ID is specified by the subnet mask. We gave a detailed example of this, using the author's subnet, and introduced variable-length subnets. The use of subnetting reduces the size of the Internet routing tables, since many networks can often be accessed through a single point. Information on the interfaces and networks is available through the ifconfig and netstat commands. This includes the IP address of the interface, its subnet mask, broadcast address, and MTU.

We finished the chapter with a discussion of potential changes to the Internet protocol suite-the next generation of IP.



TCP.IP Illustrated, Volume 1. The Protocols
TCP/IP Illustrated, Vol. 1: The Protocols (Addison-Wesley Professional Computing Series)
ISBN: 0201633469
EAN: 2147483647
Year: 1993
Pages: 378

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