Chapter 6, Routing IP

Chapter 6, Lesson 1

Understanding IP Routing

1. Routing Principles

A. The network layer is primarily responsible for end-to-end communications on an internetwork.

1. Network layer protocols such as IP are responsible for ensuring that packets arrive at their destination intact.

2. This task requires network layer protocols to have knowledge of the other networks around them.

|1| B. A router is a device with two or more network interfaces, with each one connected to a different network.

1. The basic function of the router is to receive data packets over one network interface and transmit them out through another interface.

2. When a router processes packets, they travel up through the protocol stack no higher than the network layer and then travel down again to be retransmitted.

a. For this reason, routers are sometimes referred to as intermediate systems.

3. The packet is processed by the entire protocol stack on the computer that originally transmitted the packet and on the final destination.

a. The source and destination computers are called end systems.

|2| Note The illustration on Slide 2 to reinforces the concept that routers are intermediate systems that process packets no higher than the network layer.

|3| C. On the simplest possible internetwork, one composed of only two network segments, the routing process consists of the following steps:

|4| 1. A packet arrives over one network interface.

2. The router strips off the data-link layer frame used to transmit the datagram over the incoming network.

3. The router reads the Destination IP Address value in the IP header.

4. If the destination is a computer on the same network as the one that originally transmitted it, the router discards the packet.

5. If the destination is a computer on the other network, the router transmits it out through the other network interface.

6. The router repackages the datagram by encapsulating it in a new data‑link layer frame, suitable for the outgoing network.

7. The router transmits the packet.

a. In an internetwork with only two network segments, the router has to make only one decision, whether to discard a packet or transmit it over the other network.

b. Because the internetwork consists of only two segments, there is only one possible destination for each packet, which is the destination end system.

|5| D. On a more complex network, such as the three-segment internetwork shown on Slide 5, the process is slightly more complex.

1. In this internetwork, two routers connect the three networks in daisy-chain fashion.

2. Each time one of the routers receives a packet, the decision-making process consists of three alternatives instead of two, as follows:

a. If the destination is a computer on the same network as the computer that originally transmitted it, the router discards the packet.

b. If the destination is a computer on the other network to which the router is attached, the router transmits the packet directly to the destination end-system.

(1) This is called a direct route, because the data-link layer destination address is the same as the network layer destination address.

c. If the destination is a computer on a network to which the router is not attached, the router transmits the packet to the other router.

(1) This is an indirect route, because the data-link layer destination is different from that of the network layer.

3. A router has direct knowledge only of the networks connected to its interfaces.

a. If a packet is destined for a computer on a network to which the router is not connected, the router must transmit the packet to another router, which will perform the same process.

4. In a three-segment network, there are only two routers, so if the destination is on an unknown network, there is only one place to send the packet.

|6| E. On an even larger internetwork such as the five-segment, three-router internetwork shown on Slide 6, the routing process is more complicated.

1. When the destination is a computer on an unknown network, the router can forward the packet to any one of several other routers.

a. On the network shown on Slide 6, for example, when Computer 1 generates a packet that is destined for Computer 3, the packet goes to Router A first.

b. Router A has no direct knowledge of the network where Computer 3 is located, so it must forward the packet to another router.

c. However, two other routers are on the internetwork, and only one of them provides access to the network with Computer 3 on it.

d. The most complex part of the routing process is deciding where to send each individual packet next.

(1) Large internetworks are often designed with redundant paths so that traffic can always reach its destination, even if a router fails.

(2) When selecting the next intermediate destination for a packet, a router can choose from multiple paths, some of which might be more efficient than others.

(3) Each router must make an intelligent routing decision when processing each packet in order to get the packet to its destination as quickly as possible.

2. Routing Tables

A. To make their routing decisions, routers need information about networks other than those to which they are attached.

1. This information is stored in what is known as a routing table, which every computer running TCP/IP maintains.

a. A routing table is a list of possible destinations with the information needed to transmit data to each destination in the most efficient manner possible.

|7| 2. The exact appearance of the routing table varies on different computing platforms; a Windows 2000 routing table is shown on Slide 7.

3. To display the routing table on any Windows computer with TCP/IP installed, type route print at the command prompt.

4. Functions of the columns in the routing table

a. Network Address. Specifies the address of the network or host for which routing information is provided in the other columns

b. Netmask. Specifies the subnet mask to be applied to the value in the Network Address column

c. Gateway Address. Specifies the IP address of the router that the system should use to send datagrams to the network or host identified in the Network Address column

d. Interface. Specifies the IP address of the network interface adapter that the computer should use to transmit packets to the system identified in the Gateway Address column

e. Metric. Contains a value that enables the system to compare the relative efficiency of routes to the same destination

B. Workstation routing

1. The sample routing table in Slide 7 contains the typical entries for a workstation running TCP/IP that is not functioning as a router.

2. The value 0.0.0.0 in the Network Address column, found in the first entry in the table, identifies the default gateway entry.

a. The default gateway is the router on the LAN that the system uses when no routing table entries match the Destination IP Address of an outgoing packet.

3. The default gateway entry in the Gateway Address column contains the IP address of a router on the local network, and the Interface column contains the IP address of the network interface adapter that connects the system to the network.

a. In TCP/IP terminology, the term “gateway” is synonymous with the term “router.”

(1) However, in other networking disciplines, a gateway can refer to a different device that connects networks at the application layer instead of the network layer.

4. The second entry contains a special IP address that is designated as the TCP/IP loopback address.

5. The third entry contains the address of the local network on which the computer is located.

a. The IP address of the network interface adapter in the computer to which this routing table belongs is 192.168.2.2.

b. The Network Address and Netmask values indicate that it is a Class C network with the address 192.168.2.0.

c. The system uses the third entry for direct routes when it transmits packets to other systems on the local network.

6. The fourth entry contains the host address of the computer itself.

a. It instructs the system to transmit data addressed to itself to the loopback address.

b. IP always searches the routing table for host address entries before network address entries.

7. The fifth and seventh entries contain broadcast addresses, both the generic IP broadcast address (255.255.255.255) and the local network’s broadcast address (192.168.2.255).

8. The sixth entry contains the network address for the multicast addresses designated by the Internet Assigned Numbers Authority (IANA) for specific purposes.

C. Router routing

1. On a computer running TCP/IP that is functioning as a router, the routing table is usually longer and more complex.

2. The router’s routing table includes the workstation routing-table entries described in section B as well as entries for other networks and hosts on the internetwork.

a. The information in these entries enables the router to select one of the other available routers to reach the destination.

|8| 3. A router on the same network as the computer with the routing table shown on Slide 7 might have the additional routing table entries shown on Slide 8.

4. The first entry indicates that to reach the 192.168.3.0 network, the router should use a gateway with the address 192.168.3.1.

5. As in the previous example on Slide 7, the second entry instructs the router to send all traffic addressed to its own network interface to the loopback address.

6. The third and fourth entries provide instructions for the router to access the 192.168.4.0 network.

a. In this case, there are two possible routes to this network:

(1) A route that uses the router’s 192.168.2.1 interface to access another router with the address 192.168.2.3

(2) A route that uses the 192.168.3.1 interface to access a router with the address 192.168.3.6

b. The difference between these two routes is indicated by the respective values in the Metric column.

(1) The significance of the Metric value can vary, depending on how the routing table entries are created, but in most cases the value indicates the number of hops needed to reach the destination.

(2) Each router that processes a packet is considered to be one hop, so these entries indicate that packets transmitted to the 192.168.4.0 network through the 192.168.2.3 gateway require one hop but packets using the 192.168.3.6 gateway are two hops away.

c. When a router has two entries for the same destination in its routing table, it always uses the one with the lower Metric value.

D. Selecting a route

|9| 1. Each time a router processes a packet, it accesses its routing table and utilizes the information there according to the sequence shown on
Slide 9 and described below.

a. The router reads the value of the Destination IP Address field in the packet’s IP header and compares it with the routing table, looking for a host address with the same value.

(1) A host address entry in the table has a full IP address in the Network Address column and the value 255.255.255.255 in the Netmask column.

b. If no host address entry in the routing table exactly matches the Destination IP Address value, the router then scans the routing table’s Network Address and Netmask columns for an entry that matches the destination address’s network identifier.

(1) If more than one entry in the routing table contains the desired network identifiers, the router uses the entry with the lower value in the Metric column.

c. If no table entries match the network identifier of the destination IP address, the router searches for a default gateway entry that has a value of 0.0.0.0 in the Network Address and Netmask columns.

d. If there is no default gateway entry, the router generates an Internet Control Message Protocol (ICMP) Destination Unreachable error message and transmits it back to the end-system that transmitted the datagram.

e. If the router locates a viable routing table entry, it prepares to transmit the datagram to the router identified in the Gateway Address column.

(1) The system consults the Address Resolution Protocol (ARP) cache or performs an ARP transaction to obtain the data-link layer hardware address of the router.

f. When it has the hardware address, the router passes it and the datagram down to the data-link layer protocol associated with the address specified in the Interface column.

(1) The data-link layer protocol constructs a frame, using the destination router’s hardware address in its Destination Address field, and transmits it out over the designated interface.

E. Routing table creation

1. How does the information get into the routing table?

a. In the example of a workstation routing table described earlier (in section B), the computer itself automatically creates the entries.

(1) The default gateway address is supplied as part of the TCP/IP client configuration, and the local network and local host entries are derived from the computer’s own IP address.

b. The routing table in a router contains entries that the computer cannot derive from its own configuration because they contain information about remote networks.

|10| 2. Entries can be created in a router’s routing table in two ways: manually and automatically.

a. The manual method is called static routing, in which an administrator uses a program to create table entries.

b. The automatic method is called dynamic routing, which uses a specialized routing protocol.

3. Dynamic routing protocols enable routers to transmit the contents of their routing tables to other routers, thereby providing them with information about remote parts of the internetwork.

4. On the Internet, the IP routing process is still more complicated because there is no way for every router on the Internet to maintain information about every other router.

a. The routing tables would be enormous and the traffic generated by the dynamic routing protocols would flood the network.

5. For a small internetwork that does not often change, static routing can be an effective routing solution.

6. On a large internetwork, dynamic routing is all but essential.

a. With a large number of routers, you have a large number of routing tables and a large number of entries in each table.

(1) Creating those entries manually on each router would be a large and complex task.

7. Advantages of dynamic routing

a. Reduces the network administrator’s workload

b. Automatically compensates for changes in the network infrastructure

(1) The process by which the routers compensate for a change of the internetwork configuration is called convergence.

3. Routing Hardware

A. On large internetworks and the Internet, a router is typically a dedicated hardware device with multiple network interfaces.

B. The most elaborate type of router, found in corporate data centers, consists of a rack-mounted frame with slots for network interface modules of various types.

1. Because routers function at the network layer of the Open Systems Interconnection (OSI) model, the data-link layer protocol used by a network is irrelevant to the routing function.

2. Modular routers enable network administrators to customize the unit to their network configuration so that they can join networks using different LAN and wide area network (WAN) protocols together.

C. A more common type of hardware router today is one that connects a LAN to another network using a WAN link.

1. These devices are frequently marketed as Internet routers because they are often used to provide LAN users with Internet access.

2. In an Internet router, one of the network interfaces is a standard LAN adapter using a protocol such as Ethernet, and the other is a WAN adapter using any of several media, such as a dial-up modem connection or a leased line.

3. Because Internet access is widespread on networks today, Internet routers are available at all levels of price and complexity.

4. An Internet router often includes additional features, such as network address translation (NAT) and other firewall technologies.

D. Switching

1. Routing is primarily used for WAN connections.

a. Most of the private networks constructed today use switches instead of routers to connect LANs.

2. A switch is a data-link layer device that looks much like a hub, with the following difference:

a. A hub receives data packets through one port and forwards them out through all the other ports.

b. A switch receives incoming data through one port and forwards it out only through the port providing access to the destination system.

(1) The result is that each pair of computers on a switched network has what amounts to a dedicated, full-bandwidth connection between them.

(2) This eliminates collisions, contention for the network medium, and the need for media access control.

3. By eliminating the shared network medium, switching joins the individual LANs into one large network.

4. Data-link layer switching requires much less processing than network layer routing, which makes a switched network faster, more efficient, and considerably less expensive than a routed network of the same configuration.

4. Routing Software

A. Although many of the routers in use today are dedicated hardware devices, routing software can sometimes provide all the processing capabilities a router needs.

B. A computer with two or more network interfaces (called a multihomed computer) can function as a router, in addition to its other capabilities.

1. Many network operating systems, including Windows 2000 Server, are capable of routing IP and other network layer protocols, such as Internetwork Packet Exchange (IPX).

2. The Routing and Remote Access Service (RRAS) included with Windows 2000 Server enables the computer to function in a variety of roles—as a router connecting two LANs, a router connecting a LAN and a remote network, a remote access server, and a NAT server, among others.

3. Some software products enable two or more users to share an Internet connection on a home or small office LAN, such as the Internet Connection Sharing (ICS) feature in Microsoft Windows XP and Microsoft Windows 2000 Professional.

Chapter 6, Lesson 2

Routing with RRAS

1. Configuring RRAS

A. All versions of Windows 2000 Server install RRAS by default with the operating system, but they do not configure or activate it.

1. This is because RRAS can perform a variety of functions, and Windows 2000 leaves it up to the system administrator to select one.

2. You must configure the service manually using the RRAS console, which provides access to wizards that aid in the process.

B. To configure RRAS to provide basic IP routing between two existing network interfaces:

1. Click Start, and then open the Routing And Remote Access console from the Administrative Tools program group to display the console.

2. In the scope pane, select the server, and then from the Action menu, select Configure And Enable Routing And Remote Access to start the Routing And Remote Access Server Setup Wizard.

|11| 3. Click Next to bypass the Welcome page and proceed to the Common Configurations page.

4. Click the Network Router option button, and then click Next to proceed to the Routed Protocols page.

5. If TCP/IP appears in the Protocols box, confirm that Yes, All Of The Available Protocols Are On This List is selected, and then click Next to proceed to the Demand-Dial Connections page.

6. Click No, and then click the Next button to proceed to the Completing The Routing And Remote Access Server Setup Wizard page.

7. Click Finish to complete the configuration process and close the wizard.

|12| a. The Routing And Remote Access console now appears, as shown on Slide 12.

C. Manually configuring RRAS

1. It is also possible to activate RRAS without configuring it to perform any particular task.

a. To do this, you start the Routing And Remote Access Server Setup Wizard and then, in the Common Configurations page, select Manually Configured Server.

b. The wizard installs all the main RRAS components without configuring them, and then terminates.

c. When the RRAS service starts, you can manually configure the components to perform the tasks you need.

2. Implementing Demand-Dial Routing

A. RRAS can route traffic between two LANs when the computer has two network interface adapters installed, or between a LAN and a remote network, using one network interface adapter and a WAN connection.

1. The latter case, you must create a demand-dial interface for the WAN connection.

a. A demand-dial interface is one in which the interface is activated only when the routing table shows that this interface is needed to reach the IP destination address.

b. The demand-dial interface can be a dial-up modem, an Integrated Services Digital Network (ISDN) adapter, or other communications device.

B. You can create a demand-dial interface in either of two ways:

1. By answering Yes on the Demand-Dial Connections page of the Routing And Remote Access Server Setup Wizard

2. By manually creating the interface after completing the RRAS Network Router configuration process

C. To manually create a demand-dial interface:

1. Click Start, and then open the Routing And Remote Access console from the Administrative Tools program group.

2. In the scope pane, select the RRAS server icon, and then select Properties from the Action menu to open the server’s Properties dialog box.

3. In the General tab, confirm that the Router check box is selected, and then click the LAN And Demand-Dial Routing option button.

4. Click OK.

a. A Routing And Remote Access message box appears, informing you that the configuration change you are making requires the RRAS service to be stopped and restarted.

5. Click Yes to stop and start the RRAS service.

6. In the scope pane, select the Routing Interfaces icon beneath the server icon, and then select New Demand Dial Interface from the Action menu to start the Demand Dial Interface Wizard.

7. Click Next to bypass the Welcome page and proceed to the Interface Name page.

8. In the Interface Name box, type a name by which the demand-dial interface will be identified in the RRAS console.

9. Click Next to proceed to the Connection Type page.

10. Click the Connect Using A Modem, ISDN Adapter, Or Other Physical Device option button, and then click Next to proceed to the Phone Number page.

11. In the Phone Number Or Address box, type the telephone number of the remote access server or router on the remote network, and then click Next to proceed to the Protocols And Security page.

|13| 12. Select the appropriate check boxes to enable the following features, and then click Next to proceed to the Dial Out Credentials page.

a. Route IP Packets On This Interface. Enables RRAS to route IP datagrams

b. Route IPX Packets On This Interface. Enables RRAS to route IPX datagrams

c. Add A User Account So A Remote Router Can Dial In. Adds a Dial In Credentials page to the wizard

d. Send A Plain-Text Password If That Is The Only Way To Connect. Enables RRAS to use unencrypted passwords when it cannot negotiate a more secure authentication protocol

e. Use Scripting To Complete The Connection With The Remote Router. Enables the use of scripts to control the connection process

13. In the User Name, Domain, Password, and Confirm Password boxes, type the credentials needed for RRAS to log on to the remote access server or router.

14. Click Next to proceed to the Completing The Demand Dial Interface Wizard page.

15. Click Finish to close the wizard and create the new demand-dial interface.

a. The interface now appears in the list of LAN And Demand-Dial Interfaces in the RRAS console’s detail pane.

D. After you have created the demand-dial interface, you create a static route to specify when RRAS should use the interface.

3. Configuring Demand-Dial Interfaces

A. After you create a demand-dial interface, you can configure its parameters to control the connection process, set the TCP/IP parameters, and secure the communications between the networks.

B. To configure a demand-dial interface, you select it in the Routing Interfaces list in the Routing And Remote Access console and select Properties from the Action menu.

4. Creating Static Routes

A. Configuring static routes using the RRAS console

1. When the RRAS service is configured and running, you can use the RRAS console to view the computer’s routing table and manage its entries.

|14| 2. To view the routing table, expand the IP Routing icon, select Static Routes, and select Show IP Routing Table from the Action menu to display the IP Routing Table window.

B. To create a new entry in the routing table:

1. Click Start, and then open the Routing And Remote Access console from the Administrative Tools program group.

2. Expand the server icon and then the IP Routing icon.

3. Select the Static Routes icon, and then select New Static Route from the Action menu to display the Static Route dialog box.

4. Using the Interface Selector, select the interface that you want the computer to use to reach the destination.

a. The Interface Selector contains all the network interfaces found in the RRAS Routing Interfaces header (except for the Loopback interface).

5. In the Destination box, type the address of the network or host for which the entry will provide routing information.

6. In the Network Mask box, type the subnet mask to be associated with the destination address.

7. In the Gateway box, specify the address of the router that RRAS should use to send traffic to the destination.

8. In the Metric field, type a value that indicates the relative efficiency of the route.

9. Select the Use This Route To Initiate Demand-Dial Connections check box if you want traffic going to the specified destination to trigger a demand-dial connection.

10. Click OK to close the dialog box and add the new entry to the routing table.

C. Using Route.exe

1. Every computer running TCP/IP—even one not functioning as a router—has a routing table.

2. All the current Windows operating systems include a command-line utility called Route.exe that enables you to view and manage the entire contents of the computer’s routing table.

|15,16| 3. The syntax for Route.exe is shown on Slides 15 and 16.

4. The Route.exe command variable takes one of the following four values:

a. Print. Displays the contents of the routing table

(1) When used with the -p parameter, it displays only the persistent routes in the routing table

b. Add. Creates a new entry in the routing table

c. Delete. Deletes an existing entry from the routing table

d. Change. Modifies the parameters of an entry in the routing table

|17| 5. Slide 17 shows an example of using static routing to forward internetwork traffic.

a. To create an entry that informs the Windows 2000 system labeled Router A of the existence of Router B on the same LAN, you would execute a Route.exe command like the following at the Router A system’s command line: ROUTE ADD 192.168.5.0 MASK 255.255.255.0 192.168.2.7 IF 192.168.2.2 METRIC 1

b. The functions of the Route.exe parameters in this command are as follows:

(1) ADD Indicates that the program should create a new entry in the existing routing table

(2) 192.168.5.0 The address of the other network to which Router B provides access

(3) MASK 255.255.255.0 The subnet mask to be applied to the destination address, which in this case indicates that the address represents an unsubnetted Class C network

(4) 192.168.2.7 The address of the network interface adapter with which Router B is connected to the same network as Router A

(5) IF 192.168.2.2 The address of the network interface adapter in Router A that provides access to the network it shares with Router B

(6) METRIC 1 Indicates that the destination network is one hop away

c. This new routing table entry essentially tells Router A that when it has traffic to send to any computer on the network with the address 192.168.5.0, it should send the traffic to the router with the address 192.168.2.7, using the Router A network interface adapter with the address 192.168.2.2.

Chapter 6, Lesson 3

Using Dynamic Routing Protocols

|18| 1. Dynamic Routing Protocols

A. Dynamic routing uses specialized routing protocols to gather and share routing information.

1. The two routing protocols supported by RRAS are the Routing Information Protocol (RIP) and the Open Shortest Path First (OSPF) protocol.

a. RIP is the simplest and most popular routing protocol used today, but OSPF is designed to address some of RIP’s shortcomings and is becoming more common.

2. A typical Windows 2000 internetwork runs one or the other of these protocols on all its routers, enabling them to continually share their routing table information.

B. RIP and OSPF are both interior routing protocols designed to provide dynamic routing services within an internetwork.

C. To prevent its saturation with routing protocol traffic, the Internet is broken up into administrative units called autonomous systems (ASs).

1. Each AS is theoretically a group of networks controlled by a single administrative body and running an interior routing protocol throughout it.

2. The interior routing protocol communications within an AS are invisible to systems outside it.

D. ASs share routing information with other ASs, using exterior routing protocols such as the Border Gateway Protocol (BGP) or the Exterior Gateway Protocol (EGP).

|19| 1. Typically, a small subset of the routers in an AS are configured to run both interior and exterior routing protocols to provide routing information to other nearby ASs.

a. These protocols are called border routers.

b. On a smaller scale, border routing can also refer to any router providing an internetwork with access to other internetworks.

c. The term “border routing” also comes into play with the OSPF routing protocol, with which you can split an internetwork into discrete areas, which are connected using area border routers.

2. Understanding RIP

A. RIP is the most commonly used interior routing protocol in the TCP/IP suite and on networks around the world.

B. Most RIP exchanges are based on two message types: requests and replies.

1. Both message types are packaged in User Datagram Protocol (UDP) packets addressed to the well-known port number 520.

|20| C. When a RIP router starts, it generates a RIP request message and transmits it as a broadcast over all its network interfaces.

1. Upon receiving the broadcast, every other router that supports RIP on either network generates a reply message that contains its routing table information.

a. A RIP reply message can contain up to 25 routes, each of which is 20 bytes long.

2. If the routing table on the replying router contains more than 25 entries, the router generates multiple reply messages until it has transmitted the entire contents of the table.

3. When the original router receives the replies, it integrates the routes they contain into its own routing table.

D. RIP routing metrics

1. The metric value included with each routing table entry determines the efficiency of the route based on the number of hops required to reach the destination.

2. When routers receive routing table entries from other routers using RIP, they increment the value of the metric for each route to reflect the additional hop required to reach the destination.

2. The maximum value for a metric in a RIP message is 15.

a. Routing that uses metrics based on the number of hops to the destination is called distance vector routing.

|21| E. RIP version 1 updates

1. The format of a RIP version 1 route is shown on Slide 21.

2. After their initial exchange, RIP routers transmit periodic updates to provide current information to all the other routers on the networks to which they are connected.

3. If a RIP-supplied routing table entry is not refreshed on a regular basis, the router assumes that the entry is no longer viable and eventually removes it from the table.

4. This frequent retransmission of routing data is the main disadvantage of RIP.

a. The protocol generates a large amount of redundant broadcast traffic.

b. In addition, the message format does not support the inclusion of a subnet mask for each route.

5. RIP version 2 was designed to address the disadvantages of RIP version 1.

F. RIP version 2

1. The primary difference between RIP 1 and RIP 2 is the format of the routes included in the reply messages.

2. The RIP 2 message is no larger than that of RIP 1, but it uses the empty fields in the RIP 1 message by including additional information about each route.

|22| 3. The format of a RIP version 2 route is shown on Slide 22.

|23| 4. Functions of the RIP version 2 route fields

a. Address Family Identifier (2 bytes). Contains a code that identifies the network layer protocol for which routing information is being provided

b. Route Tag (2 bytes). Contains an AS number that enables RIP to communicate with exterior routing protocols

c. IP Address (4 bytes). Specifies the address of the network or host for which routing information is being provided

d. Subnet Mask (4 bytes). Contains the subnet mask that the router should apply to the IP Address value

e. Next Hop IP Address (4 bytes). Specifies the address of the gateway that the router should use to forward traffic to the network or host specified in the IP Address field

f. Metric (4 bytes). Contains a value that specifies the relative efficiency of the route

5. The other main difference between RIP version 1 and RIP version 2 is that the latter supports the use of multicast transmissions.

3. Installing RIP

A. To use RIP on a Windows 2000 network, you must install the protocol in RRAS and bind it to the computer’s network interfaces.

1. After you have installed and configured RIP, it requires little or no monitoring.

B. To install and configure RIP:

1. Click Start, and then open the Routing And Remote Access console from the Administrative Tools program group.

2. Expand the server icon and the IP Routing icon.

|24| 3. Select the General icon, and then select New Routing Protocol from the Action menu to display the New Routing Protocol dialog box.

4. In the Routing Protocols list, select RIP Version 2 For Internet Protocol, and then click OK.

a. A new RIP icon appears beneath the IP Routing icon.

5. Select the RIP icon, and then select New Interface from the Action menu to display the New Interface For RIP Version 2 For Internet Protocol dialog box.

|25| 6. In the Interfaces list, select an interface on which you want to use RIP, and then click OK to open the RIP Properties dialog box for that interface.

7. Select the Operation mode for RIP on the selected interface, using the drop-down list provided.

8. In the Outgoing Packet Protocol drop-down list, specify the type of RIP messages RRAS should transmit over the interface, choosing from the following options:

a. RIP Version 1 Broadcast. Causes RRAS to transmit RIP messages as broadcasts using the version 1 format

b. RIP Version 2 Broadcast (default). Causes RRAS to transmit RIP messages as broadcasts using the version 2 format

c. RIP Version 2 Multicast. Causes RRAS to transmit RIP messages as multicasts using the version 2 format

(1) To use multicast transmissions with RIP, you must install the Internet Group Management Protocol (IGMP) as an RRAS routing protocol.

d. Silent RIP. Prevents RRAS from generating outgoing RIP traffic but allows the service to process and use incoming RIP messages

9. From the Incoming Packet Protocol drop-down list, specify the type of incoming RIP messages that RRAS should process, choosing from the following options:

a. Ignore Incoming Packets. Prevents RRAS from processing any incoming RIP packets, despite the Outgoing Packet Protocol value

b. RIP Version 1. Enables RRAS to process only incoming messages that use the RIP version 1 format

c. RIP Version 2. Enables RRAS to process only incoming messages that use the RIP version 2 format

d. RIP Version 1 And 2 (default). Enables RRAS to process incoming messages that use both the RIP version 1 and RIP version 2 formats

10. In the Added Cost For Routes selector, specify the factor by which RRAS should augment the metric value of incoming RIP routes.

11. Click OK to configure RIP for the selected interface.

C. If you want to use RIP on more than one network, you must add and configure each interface separately.

4. Understanding OSPF

A. Judging routes by the number of hops required to reach a destination, as in distance vector routing, is not always efficient.

1. A hop can refer to anything from a Gigabit Ethernet connection at 1000 Mbps to a dial-up modem line at 56 Kbps.

2. As a result, it is entirely possible for traffic moving over a route with a smaller number of hops to take longer than traffic with more hops.

|26| B. Another type of routing called link-state routing measures the properties of each connection.

1. The most common interior routing protocol that uses this method is the Open Shortest Path First (OSPF) protocol, as defined in RFC 2328.

a. OSPF uses a formula called the Dijkstra algorithm to rate the efficiency of a route based on several criteria in addition to the hop count, including the transmission speed of the link, delays caused by network traffic congestion, and a route cost value specified by the network administrator.

b. The link-state routing used by OSPF is more complex than distance vector routing and requires more processing by the routers themselves.

c. OSPF also uses less network bandwidth than RIP because it generates messages only when network conditions change.

2. Link-state routing is far more precise in its determination of a route’s relative efficiency, and it enables the routers to compensate for changes in the network configuration more quickly.

C. With OSPF it is possible to split an AS into discrete units called areas.

1. An area is a group of networks within an internetwork joined to other areas with backbones.

2. Most OSPF routers are configured to maintain routing information only about the networks in the local area.

3. For routing communications between areas, there are special OSPF routers called area border routers.

5. Installing OSPF

A. The process of installing the OSPF protocol is the same as that for RIP.

|27| B. In the OSPF Properties dialog box, you can configure the parameters in the following tabs:

1. General. In addition to setting event logging options for OSPF, you can specify an IP address by which the router will identify itself and indicate whether RRAS should function as an OSPF autonomous system boundary router.

2. Areas. Allows you to create and configure the OSPF areas that make up your internetwork

3. Virtual Interfaces. Allows you to create virtual links between pairs of OSPF area border routers that are not both directly connected to the backbone

3. External Routing. Allows you to specify exactly which other types of routing data you want RRAS to share with other ASs

a. Activated only when you select the Enable Autonomous System Boundary Router check box