Figure 89 RIP can deliver datagrams to gateways

NehMor* AudancmoLifl syslen

172.31.1 NetwoeK i 31

NehMor* AudancmoLifl syslen

172.31.1 NetwoeK i 31

In Figure 8-9, host 172.31.253.5 needs to transmit an IP packet to host number 192.168.125.10. This address is unknown to Router C. The router checks the subnet mask and finds it set to 2 55.255.255.0. From this, it is easy to deduce that 192.168.125 is a network number. More importantly, Router C knows a route to that subnet. Router B assumes that the gateway router at that subnet knows how to reach that host. Consequently, Router C forwards the packet to that gateway. This approach requires hosts to be known only to the router that is closest and not known throughout a network. The finely dotted lines in Figure 8-9 illustrate the two parts of the IP packet's journey: Its trip from Router B to the Router A and from A to host 192.168.125.10.

Note This section assumes that there is only one subnet mask for each network. This is a simplifying assumption. It is quite likely that a network may contain multiple networks, each with its own subnet mask.

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