TCP IP Illustrated

The most common daemons used on unix systems are the

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Unformatted text preview: e., silently discarded). In Figure 9.1 we also show a routing daemon, which is normally a user process. The most common daemons used on Unix systems are the programs routed and gated. (The term daemon means the process is running "in the background," carrying out operations on behalf of the whole system. Daemons are normally started when the system is bootstrapped and run as long as the system is up.) The topics of which routing protocol to use on a given host, how to exchange routing information with adjacent routers, and how the routing protocols work are complex and can fill an entire book of their own. (Interested readers are referred to [Periman 1992] for many of the details.) We'll look briefly at dynamic routing and the Routing Information Protocol (RIP) in Chapter 10. Our main interest in the current chapter is how a single IP layer makes its routing decisions. The routing table that we show in Figure 9.1 is accessed frequently by IP (on a busy host this could mean hundreds of times a second) but is updated much less frequently by a routing daemon (possibly about once every 30 seconds). The routing table can also be updated when ICMP "redirect" messages are received, something we'll look at in Section 9.5, and by the route command. This command is often executed when the system is bootstrapped, to install some initial routes. We'll also use the netstat command in this chapter to display the routing table. file:///D|/Documents%20and%20Settings/bigini/Docum...i/homenet2run/tcpip/tcp-ip-illustrated/ip_rout.htm (1 of 17) [12/09/2001 14.46.50] Chapter 9. IP Routing Figure 9.1 Processing done at the IP layer. 9.2 Routing Principles The place to start our discussion of IP routing is to understand what is maintained by the kernel in its routing table. The information contained in the routing table drives all the routing decisions made by IP. In Section 3.3 we listed the steps that IP performs when it searches its routing table. 1. Search for a matching host address. 2. Search for a matching network address. 3. Search for a d...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

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