estination network, the default gateway is not involved. Should a valid public network be misused internally, your users will never be able to get to any services on that valid public network. Figure 34-1 shows an example of an improperly used public IP network. In this exam- ple, the world's most interesting web page has a legitimate IP address of 25.25.25.40, with a subnet mask of 255.255.255.0. Bob, in Company A, has an improperly used IP address of 25.0.0.15, with a subnet mask of 255.0.0.0. What is important to under- stand in this example is that, even though the subnet masks are different, no one in either Company A or Company B can get to the world's most interesting web page. 25.25.25.40/24 25.25.25.0/24 Internet World's most interesting webpage Company A Company B 25.0.0.0/8 192.168.1.0/24 25.0.0.15/8 192.168.1.18/24 Sally Figure 34-1. Invalid use of a public IP network Chapter 34: IP Design Bob cannot get to the world's most interesting web page because as far as the rout- ers are concerned, he is on the same IP network as the destination. The IP stack on his machine will assume that because the destination is on the same network, it does not need to forward the packets to the default gateway. In this case, Bob's computer will either send the packets to a local device (should one exist with the same IP address as the world's most interesting web page), or fail to resolve the IP address to a local MAC address. Either way, Bob will never be able to see the world's most interesting web page. Assuming Company B would like its employees or servers to be able to get to Company A's devices (why else would there be a link?), the router connecting Company B to the Internet must have a route to Company A's network; in this case, 25.0.0.0 255.0.0.0. As the default route will only be used if there are no matching routes in the routing table, and because, in this case, there is a matching route in the routing table, the packets des- tined for the world's most interesting web page will be forwarded to Company Theref