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Common Routing Scenarios

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Applies To: Windows Server 2008

You can use routers in many different topologies and network configurations. This topic describes three typical routing scenarios.

Simple routing scenario

The following illustration shows a simple network configuration with a server running Routing and Remote Access that connects two local area network (LAN) segments (Networks A and B). In this configuration, routing protocols are not required because the router is connected to all of the networks to which it needs to route packets.

Multiple-router scenario

The following illustration shows a more complex router configuration.

In this configuration, there are three networks (Networks A, B, and C) and two routers (Routers 1 and 2). Router 1 is on Networks A and B, and Router 2 is on Networks B and C. Router 1 must notify Router 2 that Network A can be reached through Router 1, and Router 2 must notify Router 1 that Network C can be reached through Router 2. This information is automatically communicated through the use of a routing protocol, such as RIP. When a user on Network A wants to communicate with a user on Network C, the user's computer on Network A forwards the packet to Router 1. Router 1 then forwards the packet to Router 2. Router 2 then forwards the packet to the user's computer on Network C.

Without the use of routing protocols, a network administrator must enter static routes into the routing tables of Router 1 and Router 2. Although static routes work, they do not scale well to larger networks or recover from changes in the network topology.

Demand-dial routing scenario

The following illustration shows a router configuration that uses demand-dialing.

Networks A and B are geographically separated and, for the amount of traffic that is transferred between the networks, a leased wide area network (WAN) link is not economical. Router 1 and Router 2 can connect over an analog phone line by using modems (or another type of connectivity, such as ISDN) on both ends. When a computer on Network A initiates communication with a computer on Network B, Router 1 establishes a phone connection with Router 2. The modem connection is maintained as long as there are packets going back and forth. When the connection is idle, Router 1 hangs up to reduce connection costs.