Routing with Windows Server 2003 : Configuring and Managing Routing Protocols (part 1) - Configuring RIP

Understanding Routing Protocols

In Routing And Remote Access, routing protocols provide communication between routers. Windows Server 2003 includes four routing protocols that can be added to the Routing And Remote Access service: the dynamic routing protocols RIP and OSPF, the multicast routing protocol IGMP Router And Proxy, and DHCP Relay Agent.

Adding and Configuring Routing Protocols

To configure a routing protocol, you must first add the routing protocol to the Routing And Remote Access console. You perform this task by right-clicking the General node within IP Routing in the Routing And Remote Access console and clicking New Routing Protocol, as shown in Figure 1.

Once the routing protocol is available for configuration in the Routing And Remote Access console, you must enable the protocol on the appropriate network interfaces. You perform this task by right-clicking the new protocol in the console tree and then clicking New Interface on the shortcut menu. After the protocol has been enabled on the appropriate interfaces, you can configure the routing protocol through the protocol properties or the interface properties.

Configuring RIP

RIP is a dynamic routing protocol that helps routers determine the best path through which to send given data. Routes to destinations are chosen according to lowest cost. By default, this cost is determined by the number of hops or routers between endpoints; however, you can manually adjust the cost of any route as needed.

Importantly, RIP discards routes that are determined to have a cost higher than 15. This feature effectively limits the size of the network in which RIP can operate. Another important feature of RIP is that RIP-enabled routers advertise their entire routing tables to each other every 30 seconds. The service therefore generates a substantial amount of network traffic.

RIP Environment

A RIP routed environment is best suited to a small-to-medium-sized, multipath, dynamic IP internetwork:

• A small-to-medium-sized internetwork is defined as 10 to 50 networks. In addition, the diameter of a RIP network cannot exceed 15 routers.

• Multipath means that multiple paths are available for packets to travel between any two endpoints on the internetwork.

• Dynamic means that the topology of the internetwork changes over time.

Advantages and Disadvantages of RIP

The main advantage of RIP is that it is easy to deploy. You can implement it on your network simply by enabling the protocol on each router. However, RIP does not scale well to large networks because of the 15-hop limitation. Other disadvantages of RIP include its high convergence times in medium-sized networks and its inability to factor costs other than hops (such as bandwidth) into the route cost metric.

Managing RIP Security

RIP includes a number of configurable security features, including authentication, peer filtering, route filters, and neighbors.

RIP Authentication

To prevent the corruption of RIP routes by an unauthorized RIP router or a malicious attacker, you can configure RIP router interfaces to use simple password authentication. Received RIP announcements that do not match the configured password are discarded. Note, however, that the password is sent in plaintext. Any user with a network sniffer such as Network Monitor can capture the RIP announcements and view the password.

You configure RIP authentication by selecting the Activate Authentication check box and specifying a password on the General tab of the RIP interface properties dialog box, as shown in Figure 2.

Peer Filtering

You can configure each RIP router with a list of routers (designated by IP address) from which RIP announcements are accepted. By default, RIP announcements from all sources are accepted. By configuring a list of RIP peers, RIP announcements from unauthorized RIP routers are discarded.

You configure RIP peer filtering on the Security tab of the global RIP Properties dialog box, as shown in Figure 3.

Route Filters

You can configure route filters on each RIP interface so that the only routes considered for addition to the routing table are those that reflect reachable network IDs within the internetwork. For example, if an organization is using subnets of the private network ID 10.0.0.0, route filtering can be used so that the RIP routers discard all routes except those within the 10.0.0.0 network ID.

You configure route filters on the Security tab of the RIP Properties dialog box, as shown in Figure 4.

Neighbors

By default, RIP either broadcasts (RIP version 1 or RIP version 2) or multicasts (RIP version 2 only) announcements. To prevent RIP traffic from being received by any node except neighboring RIP routers, the server running Routing And Remote Access can unicast RIP announcements.

You configure RIP neighbors on the Neighbors tab of the RIP Properties dialog box, as shown in Figure 5.