TCP IP Illustrated

With another telnet connection the reference count

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Unformatted text preview: stablished a Telnet connection between the two hosts svr4 and slip, we would see the reference count go to 1. With another Telnet connection the reference count would go to 2, and so on. The next column ("use") displays the number of packets sent through that route. If we are the only users of the route and we run the ping program to send 5 packets, the count goes up by 5. The final column, the interface, is the name of the local interface. The second line of output is for the loopback interface (Section 2.7), always named lo0. The G flag is not set, since the route is not to a gateway. The H flag indicates that the destination address ( is a host address, and not a network address. When the G field is not set, indicating a direct route, the gateway column gives the IP address of the outgoing interface. The third line of output is for the default route. Every host can have one or more default routes. This entry says to send packets to the router (sun) if a more specific route can't be found. This means the current host (svr4) can access other systems across the Internet through the router sun (and its SLIP link), using this single routing table entry. Being able to establish a default route is a powerful concept. The flags for this route (UG) indicate that it's a route to a gateway, as we expect. Here we purposely call sun a router and not a host because when it's used as a default router, its IP forwarding function is being used, not its host functionality. The Host Requirements RFC specifically states that the IP layer must support multiple default routes. Many implementations, however, don't support this. When multiple default routes exist, a common technique is to round robin among them. This is what Solaris 2.2 does, for example. The final line of output is for the attached Ethernet. The H flag is not set, indicating that the destination address ( is a network address with the host portion set to 0. Indeed, the low-order 5 bits are 0 (Figure 3.11). Sinc...
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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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