C-12 User’s Reference Guide
Routers B and C (which could also be Netopia R2020s) serve the two remote networks that are subnets of a.b.c.0. The subnetting is accomplished by configuring the Netopia R2020 with connection profiles for Routers B and C (see the following table).
Connection profile | Remote IP address | Remote IP mask | Bits available for host | |
address | ||||
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for Router B | a.b.c.128 | 255.255.255.192 | 7 | |
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for Router C | a.b.c.248 | 255.255.255.248 | 3 | |
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The Netopia R2020’s connection profiles for Routers B and C create entries in its IP routing table. One entry points to the subnet a.b.c.128, while a second entry points to the subnet a.b.c.248. The IP routing table might look similar to the following:
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| IP Routing Table |
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Network | via | |||
SCROLL |
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0.0.0.0 | 0.0.0.0 | a.b.c.1 WAN | 3719 | Management |
127.0.0.1 | 255.255.255.255 127.0.0.1 lp1 | 6423 | Local | |
a.b.c.128 | 255.255.255.192 a.b.c.128 WAN | 5157 | Local | |
a.b.c.248 | 255.255.255.248 a.b.c.248 WAN | 6205 | Local | |
UPDATE
Let’s see how a packet from the Internet gets routed to the host with IP address a.b.c.249, which is served by Router C. The packet first arrives at Router A, which delivers it to its local network (a.b.c.0). The packet is then received by the Netopia R2020, which examines its destination IP address.
The Netopia R2020 compares the packet’s destination IP address with the routes in its IP routing table. It begins with the route at the bottom of the list and works up until there’s a match or the route to the default gateway is reached.
When a.b.c.249 is masked by the first route’s subnet mask, it yields a.b.c.248, which matches the network address in the route. The Netopia R2020 uses the connection profile associated with the route to connect to Router C, and then forwards the packet. Router C delivers the packet to the host on its local network.
