• interconnected LANs that provide access to computers or file servers in other locations
• higher bandwidth onto the LANs to satisfy the needs of the end users
• support technologies that can be relayed for WAN service

• to divide the interrelated aspects of network operations into less complex elements
• to define standard interfaces for plug-and-play compatibility and multivendor integration
• to enable engineers to focus their design and development efforts on a particular layer's functions
• to promote symmetry of the different internetwork modular functions for the purpose of interoperability
• to prevent changes in one area from significantly affecting other areas, so that each area can evolve more quickly
• to divide the complex operations of internetworking into discrete, more easily learned operational subsets

Each layer of the seven-layer OSI reference model serves a specific function. The functions are defined by the OSI and can be used by any network products vendor. -

The layers are:

• Application -- The application layer provides network services to user applications. For example, a word processing application is serviced by file transfer services at this layer.
• Presentation -- This layer provides data representation and code formatting. It ensures that the data that arrives from the network can be used by the application, and it ensures that the information sent by the application can be transmitted on the network.
• Session -- This layer establishes, maintains, and manages sessions between applications.
• Transport -- This layer segments and reassembles data into a data stream. TCP is one of the transport layer protocols used with IP.
• Network -- This layer determines the best way to move data from one place to another. Routers operate at this layer. You will find the IP (Internet Protocol) addressing scheme at this layer.
• Data Link -- This layer prepares a datagram (or packet) for physical transmission across the medium. It handles error notification, network topology, and flow control. This layer uses Media Access Control (MAC) addresses.
• Physical -- This layer provides the electrical, mechanical, procedural, and functional means for activating and maintaining the physical link between systems. This layer uses physical media such as twisted-pair, coaxial, and fiber-optic cable.

Step 1
A computer converts an e-mail message into alphanumeric characters that can be used by the internetworking system. This is the data.

Step 2
The message data is then segmented for transport on the internetwork system by the transport layer. The transport layer ensures that the message hosts at both ends of the e-mail system can reliably communicate.

Step 3
The data is then converted to a packet, or datagram, by the network layer. The packet also contains a network header that includes a source and destination logical address. The address helps network devices send the packet across the network along a chosen path.

Step 4
Each data-link layer device puts the packet into a frame. The frame enables the device to connect to the next directly-connected network device on the link.

Step 5
The frame is changed to a pattern of 1s and 0s for transmission on the medium (usually a wire). A clocking function enables the devices to distinguish bits as they travel across the medium.
The medium on the physical internetwork can vary along the path. For example, an e-mail message may originate on a LAN, cross a campus backbone, and continue through a WAN link until it reaches its destination on another remote LAN.

The Ethernet and IEEE 802.3 standards define a bus topology LAN that operates at a baseband signaling rate of 10 Mbps. Figure illustrates the three defined wiring standards:

• 10BASE2 (thin Ethernet) -- allows coaxial cable network segments up to 185 m. long
• 10BASE5 (thick Ethernet) -- allows coaxial cable network segments up to 500 m. long
• 10BASE-T -- carries Ethernet frames on inexpensive twisted-pair wiring

The 10BASE5 and 10BASE2 standards provide access for several stations to the same LAN segment. Stations are attached to the segment by a cable that runs from an attachment unit interface (AUI) in the station to a transceiver that is directly attached to the Ethernet coaxial cable.

Because 10BASE-T provides access for a single station only, stations that are attached to an Ethernet LAN by 10BASE-T are almost always connected to a hub or a LAN switch. In this arrangement, the hub or LAN switch is the same as an Ethernet segment.

The Ethernet and 802.3 data links prepare data for transport across the physical link that joins two devices.  For example, as Figure shows, three devices can be directly attached to each other over the Ethernet LAN. The Macintosh on the left and the Intel-based PC in the middle show MAC addresses used by the data link layer. The router on the right also uses MAC addresses for each of the LAN side interfaces. The Ethernet/802.3 interface on the router uses the Cisco IOS interface type abbreviation "E" followed by an interface number (e.g. "0", as shown in Figure ).

Broadcasting is a powerful tool that can send a single frame to many stations at the same time.  Broadcasting uses a data link destination address of all 1s (FFFF.FFFF.FFFF in hexadecimal). As Figure shows, if station A transmits a frame with a destination address of all 1s, stations B, C, and D will all receive and pass the frame to their upper layers for further processing.

When improperly used, broadcasting can seriously affect the performance of stations by unnecessarily interrupting them. Broadcasts should, therefore, be used only when the MAC address of the destination is unknown, or when the destination is all stations.

Subnets improve the efficiency of network addressing. Adding subnets does not change how the outside world sees the network, but within the organization, there is additional structure. In Figure , the network 172.16.0.0 is subdivided into four subnets: 172.16.1.0, 172.16.2.0, 172.16.3.0, and 172.16.4.0. Routers determine the destination network by using the subnet address, which limits the amount of traffic on the other network segments.

From an addressing standpoint, subnets are an extension of a network number. Network administrators determine the size of subnets based on the expansion needs of their organizations. Network devices use subnet masks to identify which part of the address is for the network and which part represents host addressing.

Example of Class C subnetting.

In Figure , the network has been assigned the Class C address 201.222.5.0. Assuming that 20 subnets are needed, with a maximum of 5 hosts per subnet, you need to subdivide the last octet into a subnet and a host, and then determine what the subnet mask will be. You need to select a subnet field size that yields enough subnetworks. In this example, selecting 5-bits gives you 20 subnets.

In the example, the subnet addresses are all multiples of 8 - 201.222.5.16; 201.222.5.32; and 201.222.5.48. The remaining bits in the last octet are reserved for the host field. The 3 bits in the example are enough for the required five hosts per subnet (actually, giving you host numbers 1 - 6). The final host addresses are a combination of the network/subnet segment's starting address plus each host's value. The hosts on the 201.222.5.16 subnet would be addressed as 201.222.5.17, 201.222.5.18, 201.222.5.19, and so forth.

A host number of 0 is reserved for the wire (or subnet) address, and a host value of all 1s is reserved because it selects all hosts-that is, it is a broadcast. A table used for the subnet planning example is on the following page. Also, a routing sample shows the combining of an arriving IP address with a subnet mask to derive the subnet address (also called the subnet number). The extracted subnet address should be typical of the subnets generated during this planning exercise.

Example of Class B subnetwork planning

In Figure , a Class B network is subnetted to provide up to 254 subnets and 254 useable host addresses. 

Example of Class C subnetwork planning

In Figure , a Class C network is subnetted to provide 6 host addresses and 30 useable subnets.

The transport layer (Layer 4) is responsible for transporting and regulating the flow of information from source to destination reliably and accurately. Its functions include:

• connection synchronization
• flow control
• error recovery
• reliability through windowing

• It ensures that senders receive acknowledgement of delivered segments.
• It provides for retransmission of any segments that are not acknowledged.
• It puts segments back into their correct sequence at the destination device.
• It provides congestion avoidance and control.

The transport layer assumes that it can use the network as a cloud to send data packets from source to destination. If you examine the operations that take place inside the cloud, you can see that one of the functions involves selecting the best paths for a given route. You begin to see the role that routers perform in this process.

• The OSI model layer functions
• Peer-to-peer communications
• Five steps of data encapsulation
• LAN devices and technologies
• Ethernet and IEEE 802.3 standards
• Carrier sense multiple access with collision detection
• Logical (IP) addressing
• MAC addressing
• TCP/IP Addressing
• Subnetworks
• Application, presentation and session layers
• Transport layer functions

Each company or organization listed on the Internet is seen as a single unique network that must be reached before an individual host within that company can be contacted. Each company network has an address; the hosts that live on that network share that same network address, but each host is identified by the unique host address on the network.

In this section, you will learn basic concepts you need to understand before configuring an IP address. By examining various network requirements, you can select the correct class of address and define how to establish IP subnets. Each device or interface must have a host number that does not have all 0s in the host field. A host address of all 1s is reserved for an IP broadcast into that network. A host value of 0 means "this network" or "the wire itself" (e.g. 172.16.0.0). A value of 0 is also used, though rarely, for IP broadcasts in some early TCP/IP implementations. The routing table contains entries for network or wire addresses; it usually contains no information about hosts.

An IP address and a subnet mask on an interface achieve three purposes:

• They enable the system to process the receipt and transmission of packets.
• They specify the device's local address.
• They specify a range of addresses that share the cable with the device.

Cisco IOS software supports two kinds of broadcasts - directed broadcasts and flooded broadcasts. Broadcasts directed into a specific network/subnet are allowed and are forwarded by the router. These directed broadcasts contain all 1s in the host portion of the address. Flooded broadcasts (255.255.255.255) are not propagated, but are considered local broadcasts. -

Example: 
/8 = 255.0.0.0 
/24 = 255.255.255.0

Lab Activity   In this lab you will work with other group members to design a 5-router network topology and an IP addressing scheme.

 

command to establish the logical network address of an interface. -

Use the

• bit count
• dotted-decimal (default)
• hexadecimal
  

IP defines a naming scheme that allows a device to be identified by its location in IP. A name such as ftp.cisco.com identifies the domain of the File Transfer Protocol (FTP) for Cisco. To keep track of domain names, IP identifies a name server that manages the name cache. DNS (Domain Name Service) is enabled by default with a server address of 255.255.255.255, which is a local broadcast. The router(config)# no ip domain-lookup command turns off name-to-address translation in the router. This means that the router will not generate or forward name system broadcast packets.

Character

Definition

!

successful receipt of an echo reply

.

timed out waiting for datagram reply

U

destination unreachable error

C

congestion-experienced packet

I

ping interrupted (e.g. Ctrl-Shift-6 X)

?

packet type unknown

&

packet TTL exceeded

NOTE: trace is supported by IP, CLNS, VINES, and AppleTalk.

When the trace reaches the target destination, an asterisk (*) is reported at the display. This is normally caused by a time out in response to one of the probe packets.

Other responses include:

!H -- The probe was received by the router, but not forwarded, usually due to an access list.
P -- The protocol was unreachable.
N -- The network was unreachable.
U -- The port was unreachable.
* -- Time out.

• In a TCP/IP environment, end stations communicate with servers or other end stations. This occurs because each node using the TCP/IP protocol suite has a unique 32-bit logical address known as the IP address.
• An IP address with a subnet address on an interface achieves three purposes:

• It enables the system to process the receipt and transmission of packets.
• It specifies the device's local address.
• It specifies a range of addresses that share the cable with the device.

• Broadcast messages are those you want every host on the network to see.
• You use the ip address command to establish the logical network address of this interface.
• The ip host command makes a static name-to-address entry in the router's configuration file.
• The ip name-server command defines which hosts can provide the name service.
• The show hosts command is used to display a cached list of host names and addresses.
• telnet, ping, and trace commands can be used to verify IP address configuration.

Lab 10.1.4 IP addressing & subnets 

Estimated time: 30 min.

Objectives:

This Lab will focus on your ability to accomplish the following tasks:

•  Design and implement a 5-router network topology 
•  Develop an IP addressing scheme based on the topology
•  Use a single Class C network address with subnets for LANs and WANs 
•  Assign IP addresses to router interfaces and hosts
•  Diagram the network using ConfigMaker

In this lab you will work with other group members to design a 5-router network topology and an IP addressing scheme. You must come up with a proper IP addressing scheme using a single Class C network address (204.204.7.0) and multiple subnets. You will then use ConfigMaker to make a diagram of the network you have designed. You have creative freedom in designing your network.

Tools / Preparation:

Prior to starting this lab you should have the equipment for the standard 5-router lab available (routers, hubs, switches, cables, etc.). Since this is a challenge lab, the routers may or may not be pre-configured with the correct IP interface settings etc. If they are, you will need to change the IP addresses to be different form those of the standard lab setup. The workstations may also be pre-configured to have the correct IP address settings prior to starting the lab. The IP addressing configuration of the workstations will also need to be changed. If the actual lab equipment is not available to configure, design the network using the worksheets provided in this lab. Work in teams of 5 or more.

The following resources will be required:

•  5 PC workstations (min.) with Windows operating system and HyperTerminal installed.
•  5 Cisco Routers (model 1600 series or 2500 series with IOS 11.2 or later).
•  4 Ethernet hubs (10BASE-T with 4 to 8 ports).
•  One Ethernet switch (Cisco Catalyst 1900 or comparable).
•  5 serial console cables to connect workstation to router console port (with RJ-45 to DB9 converters).
•  4 Sets of V.35 WAN serial cables (DTE male/ DCE female) to connect from router to router.
• CAT5 Ethernet Cables wired straight through to connect routers and workstations to hubs and switches.
•  AUI (DB15) to RJ-45 Ethernet transceivers (Quantity depends on the number of routers with AUI ports) to convert router AUI interfaces to 10BASE-T RJ-45.

Step 1 - Design the physical topology of the network.

You should have at least 5 routers in different geographical locations. You should have at least one Ethernet LAN off of each router. Sketch out the topology as you go. Answer the following questions to assist in planning:

1. How many routers will you have?
 

2. Where will the routers be located?
 

3. How many switches will you have?
 

Step 2 - Develop an IP addressing scheme.

Review your topology sketch from step one. Using a single Class C address of 204.204.7.0, create a subnetwork design for your topology. Document your scheme by indicating where you will put each of the subnets. Answer the following questions to assist in planning.

4. How many LANs are there?
 

5. How many WANs are there?
 

6. How many unique subnets will you need?
 

7. How many hosts per subnet (LAN and WAN) will you have?
 

8. How many IP addresses (hosts + router interfaces) will be required?
 

9. What is your Class C network address?
 

10. How many bits will you borrow from the host portion of the network address?  

11. What will your subnet mask be?
 

12. How many total useable subnets will this allow for?  

13. How many hosts per subnet will this allow for?
 

Step 3 - Assign IP addresses to each device interface.

Using the table assign an IP address to each device interface or range of devices (hosts) that will require an IP address. Switches do not require an IP address but you may assign one if you want to. Hubs will not have an IP address. (answers will vary)

Device name / model	Interface	IP address	Subnet mask	Default gateway

14. Which interfaces will require clock rate to be set? 

Step 4 - Diagram the network using ConfigMaker.

Use Cisco ConfigMaker to create a network diagram and add all configuration information such as IP addresses and subnet masks. ConfigMaker will allow you to enter all interface IP addresses and help you create a finished diagram. You should be familiar with ConfigMaker if you have completed lab 6.5.2.2. Use the web site listed in the overview section to download ConfigMaker if you do not have it.

Reflection:
 
 
 
 
 

Lab 10.4.1 Topology challenge lab 

Estimated time: 30 min.

Objectives:

You and your group members have just received your Cisco certification. Your first job is to work with other group members in designing a topology and IP addressing scheme. It will be a 5-router topology similar to the standard 5-router lab diagram as shown but with a few changes.  Refer to the modified 5-router lab diagram shown in the worksheet. You must come up with a proper IP addressing scheme using multiple Class C addresses which are different from those of the standard lab setup. You will then use ConfigMaker to do your own diagram of the network. You may do this lab using the worksheets or work with the actual lab equipment if it is available.

Tools / Preparation:

Prior to starting this lab you should have the equipment for the standard 5-router lab available (routers, hubs, switches, cables, etc.). Since this is a challenge lab, the routers may or may not be configured with IP interface settings etc. If they are, you will need to change the IP addresses to be different from those of the standard lab setup. The IP address configuration of the workstations will also need to be changed. If the actual lab equipment is not available to configure, design the network using the worksheets provided in this lab. Work in teams of 5 or more.

The following resources will be required:

• 5 PC workstations (min.) with Windows operating system and HyperTerminal installed. 
• 5 Cisco Routers (model 1600 series or 2500 series with IOS 11.2 or later). 
• 4 Ethernet hubs (10BASE-T with 4 to 8 ports).
• One Ethernet switch (Cisco Catalyst 1900 or comparable).
• 5 serial console cables to connect workstation to router console port (with RJ-45 to DB9 converters).
• 4 Sets of V.35 WAN serial cables (DTE male/ DCE female) to connect from router to router.
• CAT5 Ethernet Cables wired straight through to connect routers and workstations to hubs and switches.
• AUI (DB15) to RJ-45 Ethernet transceivers (Quantity depends on the number of routers with AUI ports) to convert router AUI interfaces to 10BASE-T RJ-45.
• Cisco ConfigMaker software (version 2.3 or later) See below for web site.

Websites Sites Required:

Notes:

Review the standard semester 2 lab diagram in the overview section of this lab and check all physical devices, cables and connections if the physical lab setup is available.

With the standard 5-router lab configuration shown in the overview section, there are eight (8) networks. Five (5) of these are Ethernet Local Area Networks (LANs) and 3 of them are serial Wide Area Networks (WANs). Review the modified setup of the lab diagrammed below. Using multiple Class C addresses similar to the existing standard lab, select addresses and document the IP addressing scheme by indicating where you will put each of the Class C addresses. Answer the following questions to assist your team in planning the network IP address scheme.

1. How many LANs are there?

2. How many WANs are there?

3. How many unique Class C network addresses will you need?

4. How many devices are there?

5. How many device interfaces will require IP addresses?

Use the table below to identify each router interface that will require an IP address.  Switches do not require an IP address but you may assign one if you want to.  Hubs will not have an IP address.

Device name / model	Interface	IP Address	Subnet mask	Default gateway

6. Which interfaces will require clock rate to be set?

Use Cisco ConfigMaker to recreate the network diagram in the worksheet and add all configuration information such as IP addresses and subnet masks. ConfigMaker will allow you to enter all interface IP addresses and help you create a finished diagram. Choose your own device names. You should be familiar with ConfigMaker if you have completed lab 6.5.2.2.

What did you learn from designing a topology with such a large group of people?

In what router mode did you spend most of your time?

Could you have done it any other way? If so how?

When doing this lab, how could a TFTP server have been useful?

In "IP Addressing," you learned the process of configuring Internet Protocol (IP) addresses. In this chapter, you will learn about the router's use and operations in performing the key internetworking function of the Open System Interconnection (OSI) reference model's network layer, Layer 3. In addition, you will learn the difference between routing and routed protocols and how routers track distance between locations. Finally, you will learn about distance-vector, link-state, and hybrid routing approaches and how each resolves common routing problems.

The network layer provides best-effort end-to-end packet delivery across interconnected networks. The network layer uses the IP routing table to send packets from the source network to the destination network. After the router determines which path to use, it proceeds with forwarding the packet. It takes the packet that it accepted on one interface and forwards it to another interface or port that reflects the best path to the packet's destination. -

To be truly practical, a network must consistently represent the paths available between routers. As Figure shows, each line between the routers has a number that the routers use as a network address. These addresses must convey information that can be used by a routing process to pass packets from a source toward a destination. Using these addresses, the network layer can provide a relay connection that interconnects independent networks.

The consistency of Layer 3 addresses across the entire internetwork also improves the use of bandwidth by preventing unnecessary broadcasts. Broadcasts invoke unnecessary process overhead and waste capacity on any devices or links that do not need to receive the broadcasts. By using consistent end-to-end addressing to represent the path of media connections, the network layer can find a path to the destination without unnecessarily burdening the devices or links on the internetwork with broadcasts.

For some network layer protocols, this relationship is established by a network administrator who assigns network host addresses according to a predetermined internetwork addressing plan. For other network layer protocols, assigning host addresses is partially or completely dynamic. Most network protocol addressing schemes use some form of a host or node address. In the graphic, three hosts are shown sharing the network number 1. -

• a path determination function
• a switching function. 

Figure illustrates how routers use addressing for these routing and switching functions. The router uses the network portion of the address to make path selections to pass the packet to the next router along the path.

The switching function allows a router to accept a packet on one interface and forward it through a second interface. The path determination function enables the router to select the most appropriate interface for forwarding a packet. The node portion of the address is used by the final router (the router connected to the destination network) to deliver the packet to the correct host.

Routed protocol is any network protocol that provides enough information in its network layer address to allow a packet to be forwarded from one host to another host based on the addressing scheme. Routed protocols define the field formats within a packet. Packets are generally conveyed from end system to end system. The Internet Protocol (IP) is an example of a routed protocol.

Routing protocols support a routed protocol by providing mechanisms for sharing routing information. Routing protocol messages move between the routers. A routing protocol allows the routers to communicate with other routers to update and maintain tables. TCP/IP examples of routing protocols are:

• RIP (Routing Information Protocol)
• IGRP (Interior Gateway Routing Protocol)
• EIGRP (Enhanced Interior Gateway Routing Protocol)
• OSPF (Open Shortest Path First)

When a host application needs to send a packet to a destination on a different network, the host addresses the data link frame to the router, using the address of one of the router's interfaces. The router's network layer process examines the incoming packet's header to determine the destination network, and then references the routing table which associates networks to outgoing interfaces.  The packet is encapsulated again in the data link frame that is appropriate for the selected interface, and queued for delivery to the next hop in the path.

This process occurs each time that the packet is forwarded through another router. At the router that is connected to the destination host's network, the packet is encapsulated in the destination LAN's data link frame type and delivered to the destination host.

Dynamic route knowledge works differently. After a network administrator enters configuration commands to start dynamic routing, the route knowledge is automatically updated by a routing process whenever new information is received from the internetwork. Changes in dynamic knowledge are exchanged between routers as part of the update process.

When a network is accessible by only one path, a static route to the network can be sufficient. This type of network is called a stub network. Configuring static routing to a stub network avoids the overhead of dynamic routing.

In this example, the company X routers possess specific knowledge of the topology of the company X network, but not of other networks. Maintaining knowledge of every other network accessible by way of the Internet cloud is unnecessary and unreasonable, if not impossible. Instead of maintaining specific network knowledge, each router in company X is informed of the default route that it can use to reach any unknown destination by directing the packet to the Internet.

Static routing allows routers to properly route a packet from network to network based on configured information. The router refers to its routing table and follows the static knowledge residing there to relay the packet to Router D. Router D does the same, and relays the packet to Router C. Router C delivers the packet to the destination host.

If the path between Router A and Router D fails, Router A will not be able to relay the packet to Router D using that static route. Until Router A is manually reconfigured to relay packets by way of Router B, communication with the destination network is impossible.

Dynamic routing offers more flexibility. According to the routing table generated by Router A, a packet can reach its destination over the preferred route through Router D. However, a second path to the destination is available by way of Router B. When Router A recognizes that the link to Router D is down, it adjusts its routing table, making the path through Router B the preferred path to the destination. The routers continue sending packets over this link.

When the path between Routers A and D is restored to service, Router A can once again change its routing table to indicate a preference for the counterclockwise path through Routers D and C to the destination network. Dynamic routing protocols can also direct traffic from the same session over different paths in a network for better performance. This is known as loadsharing.

• maintenance of a routing table
• timely distribution of knowledge, in the form of routing updates, to other routers 

Dynamic routing relies on a routing protocol to share knowledge among routers. A routing protocol defines the set of rules used by a router when it communicates with neighboring routers. For example, a routing protocol describes:

• how to send updates
• what knowledge is contained in these updates
• when to send this knowledge
• how to locate recipients of the updates

When a routing algorithm updates a routing table, its primary objective is to determine the best information to include in the table. Each routing algorithm interprets what is best in its own way. The algorithm generates a number, called the metric value, for each path through the network. Typically, the smaller the metric number, the better the path.

You can calculate metrics based on a single characteristic of a path; you can calculate more complex metrics by combining several characteristics. The metrics most commonly used by routers are as follows:

• bandwidth -- the data capacity of a link; (normally, a 10 Mbps Ethernet link is preferable to a 64 kbps leased line)
• delay -- the length of time required to move a packet along each link from source to destination
• load -- the amount of activity on a network resource such as a router or link
• reliability -- usually refers to the error rate of each network link
• hop count -- the number of routers a packet must travel through before reaching its destination
• ticks -- the delay on a data link using IBM PC clock ticks (approximately 55 milliseconds).
• cost -- an arbitrary value, usually based on bandwidth, monetary expense, or other measurement, that is assigned by a network administrator

• distance vector; or 
• link state. 

The distance-vector routing approach determines the direction (vector) and distance to any link in the internetwork. The link-state (also called shortest path first) approach re-creates the exact topology of the entire internetwork (or at least the portion in which the router is situated). 

The balanced hybrid approach combines aspects of the link-state and distance-vector algorithms. The next several pages cover procedures and problems for each of these routing algorithms and present techniques for minimizing the problems.

When all routers in an internetwork are operating with the same knowledge, the internetwork is said to have converged. Fast convergence is a desirable network feature because it reduces the period of time in which routers would continue to make incorrect/wasteful routing decisions.

Each router receives a routing table from its directly connected neighboring routers. For example, in the graphic, Router B receives information from Router A. Router B adds a distance-vector number (such as a number of hops), which increases the distance vector and then passes this new routing table to its other neighbor, Router C. This same step-by-step process occurs in all directions between direct-neighbor routers.

The algorithm eventually accumulates network distances so that it can maintain a database of network topology information. Distance-vector algorithms do not, however, allow a router to know the exact topology of an internetwork.

Without countermeasures to stop the process, the distance vector (metric) of hop count increments each time the packet passes through another router. These packets loop through the network because of wrong information in the routing tables.

With this approach, the routing protocol permits the routing loop to continue until the metric exceeds its maximum allowed value. The graphic shows the metric value as 16 hops, which exceeds the distance-vector default maximum of 15 hops, and the packet is discarded by the router. In any case, when the metric value exceeds the maximum value, Network 1 is considered unreachable.

• link-state advertisements (LSAs)
• a topological database
• the SPF algorithm, and the resulting SPF tree
• a routing table of paths and ports to each network

Engineers have implemented this link-state concept in OSPF (Open Shortest Path First) routing. RFC 1583 contains a description of OSPF link-state concepts and operations.

• keeps track of its neighbors: each neighbor's name, whether the neighbor is up or down, and the cost of the link to the neighbor.
• constructs an LSA packet that lists its neighbor router names and link costs, including new neighbors, changes in link costs, and links to neighbors that have gone down.
• sends out this LSA packet so that all other routers receive it.
• when it receives an LSA packet, records the LSA packet in its database so that it updates the most recently generated LSA packet from each router.
• completes a map of the internetwork by using accumulated LSA packet data and then computes routes to all other networks by using the SPF algorithm.

Each time an LSA packet causes a change to the link-state database, the link-state algorithm (SPF) recalculates the best paths and updates the routing table. Then, every router takes the topology change into account as it determines the shortest path to use for packet routing.

	Web Links
	Dijkstra's algorithm

 

 

Processing and memory requirements
Running link-state routing protocols in most situations requires that routers use more memory and perform more processing than distance-vector routing protocols. Network administrators must ensure that the routers they select are capable of providing these necessary resources.

Routers keep track of all other routers in a group and the networks that they can each reach directly. For link-state routing, their memory must be able to hold information from various databases, the topology tree, and the routing table. Using Dijkstra's algorithm to compute the SPF requires a processing task proportional to the number of links in the internetwork, multiplied by the number of routers in the internetwork.

Bandwidth requirements
Another cause for concern involves the bandwidth that must be consumed for initial link-state packet flooding. During the initial discovery process, all routers using link-state routing protocols send LSA packets to all other routers. This action floods the internetwork as routers make their en masse demand for bandwidth, and temporarily reduce the bandwidth available for routed traffic that carries user data. After this initial flooding, link-state routing protocols generally require only minimal bandwidth to send infrequent or event-triggered LSA packets that reflect topology changes.

If LSA distribution to all routers is not done correctly, link-state routing can result in invalid routes. Scaling up with link-state protocols on very large internetworks can expand the problem of faulty LSA packet distribution. If one part of the network comes up first with other parts coming up later, the order for sending and receiving LSA packets will vary. This variation can alter and impair convergence. Routers might learn about different versions of the topology before they construct their SPF trees and routing tables. On a large internetwork, parts that update more quickly can cause problems for parts that update more slowly.

• Distance-vector routing gets topological data from the routing table information of its neighbors. Link-state routing obtains a wide view of the entire internetwork topology by accumulating all necessary LSAs.
• Distance-vector routing determines the best path by adding to the metric value that it receives as routing information is passed from router to router. For link-state routing, each router works separately to calculate its own shortest path to destination networks.
• With most distance-vector routing protocols, updates for topology changes come in periodic table updates. The information passes from router to router, usually resulting in slower convergence. With link-state routing protocols, updates are usually triggered by topology changes. Relatively small LSAs passed to all other routers usually result in faster time to converge on any internetwork topology change.

The balanced-hybrid routing protocol converges rapidly, like the link-state protocols. However, it differs from distance-vector and link-state protocols by using fewer resources such as bandwidth, memory, and processor overhead. Examples of hybrid protocols are OSI's IS-IS (Intermediate System-to-Intermediate System), and Cisco's EIGRP (Enhanced Interior Gateway Routing Protocol).

The Figure shows an example of this with LAN-to-LAN routing. In this example, packet traffic from source Host 4 on Ethernet Network 1 needs a path to destination Host 5 on Network 2. The LAN hosts depend on the router and its consistent network addressing to find the best path.

When the router checks its routing table entries, it discovers that the best path to destination Network 2 uses outgoing port To0, the interface to a token-ring LAN. Although the lower-layer framing must change as the router passes packet traffic from Ethernet on Network 1 to token-ring on Network 2, the Layer 3 addressing for source and destination remains the same. In the Figure, the destination address remains Network 2, Host 5, regardless of the different lower-layer encapsulations.

Routers enable LAN-to-WAN packet flow by keeping the end-to-end source and destination addresses constant while encapsulating the packet in data link frames, as appropriate, for the next hop along the path.

In addition to the basic switching and routing functions, routers have a variety of additional features that help to improve the cost-effectiveness of the internetwork. These features include sequencing traffic based on priority and traffic filtering.

Typically, routers are required to support multiple protocol stacks, each with its own routing protocols, and to allow these different environments to operate in parallel. In practice, routers also incorporate bridging functions and sometimes serve as a limited form of hub.

• Internetworking functions of the network layer include network addressing and best path selection for traffic.
• In network addressing, one part of the address is used to identify the path used by the router and the other is used for ports or devices on the network.
• Routed protocols allow routers to direct user traffic; routing protocols work between routers to maintain routing tables.
• Network discovery for distance-vector routing involves exchange of routing tables; problems can include slow convergence.
• For link-state routing, routers calculate the shortest paths to other routers; problems can include inconsistent updates.
• Balanced hybrid routing uses attributes of both link-state and distance-vector routing.

With the setup mode command facility, you can answer questions in the system configuration dialog. This facility prompts you for basic configuration information. The answers you enter allow the router to use a sufficient, but minimal-feature, router configuration that includes the following: 

• an inventory of interfaces
• an opportunity to enter global parameters
• an opportunity to enter interface parameters
• a setup script review
• an opportunity to indicate whether you want the router to use this configuration

After you approve setup mode entries, the router uses the entries as a running configuration. The router also stores the configuration in NVRAM as a new startup-config, and you can start using the router. For additional protocol and interface changes, you can use the enable mode and enter the command configure.

In the lab that follows, you will start up your router in a just-received condition, a state that lacks another source for the startup configuration. This condition on the router will permit you to use the setup-mode command facility and answer prompts for basic configuration information. The answers you enter will include address-to-port commands to set up router interfaces for IP.

By default, routers learn paths to destinations three different ways :

• static routes -- manually defined by the system administrator as the next hop to a destination; useful for security and traffic reduction
• default routes -- manually defined by the system administrator as the path to take when there is no known route to the destination
• dynamic routing -- the router learns of paths to destinations by receiving periodic updates from other routers.

The ip route command sets up a static route. -

The administrative distance is a rating of the trustworthiness of a routing information source, expressed as a numeric value from 0 to 255. The higher the number, the lower the trustworthiness rating.

A static route allows manual configuration of the routing table. No dynamic changes to this table entry will occur as long as the path is active. A static route may reflect some special knowledge of the networking situation known to the network administrator. Manually-entered administrative distance values for static routes are usually low numbers (1 is the default). Routing updates are not sent on a link if they are only defined by a static route, therefore, they conserve bandwidth.

The assignment of a static route to reach the stub network 172.16.1.0 is proper for Cisco A because there is only one way to reach that network. The assignment of a static route from Cisco B to the cloud networks is also possible. However, a static route assignment is required for each destination network, in which case a default route may be more appropriate. -

Lab Activity    In this lab you will configure a static route between neighboring routers.

The ip default-network command establishes a default route in networks using dynamic routing protocols.. -

Default routes keep routing tables shorter. When an entry for a destination network does not exist in a routing table, the packet is sent to the default network. Because a router does not have complete knowledge about all destination networks, it can use a default network number to indicate the direction to take for unknown network numbers. Use the default network number when you need to locate a route but have only partial information about the destination network. The ip default-network command must be added to all routers in the network or used with the additional command redistribute static so all networks have knowledge of the candidate default network.

In the example, the global command ip default-network 192.168.17.0 defines the Class C network 192.168.17.0 as the destination path for packets that have no routing table entries. The Company X administrator does not want updates coming in from the public network. Router A could need a firewall for routing updates. Router A may need a mechanism to group those networks that will share Company X's routing strategy. One such mechanism is an autonomous system number.

• RIP -- a distance-vector routing protocol
• IGRP -- Cisco's distance-vector routing protocol
• OSPF -- a link-state routing protocol 
• EIGRP -- a balanced hybrid routing protocol

The following sections show you how to configure the first two of these protocols.

• It is a distance-vector routing protocol.
• Hop count is used as the metric for path selection.
• If the hop count is greater than 15, the packet will be discarded.
• By default, routing updates are broadcast every 30 seconds.
  

• router rip -- selects RIP as the routing protocol
• network 1.0.0.0 -- specifies a directly connected network
• network 2.0.0.0 -- specifies a directly connected network

The Cisco A router interfaces that are connected to networks 1.0.0.0 and 2.0.0.0 send and receive RIP updates. These routing updates allow the router to learn the network topology.

The router in the example sends updated routing table information every 30 seconds (configured interval). Seventeen seconds have elapsed since it sent its last update; it will send the next one in 13 seconds. Following the "Routing for Networks" line, the router specifies routes for the listed networks. The last line shows that the RIP administrative distance is 120.

 

IGRP is a distance-vector routing protocol developed by Cisco. IGRP sends routing updates at 90 second intervals, advertising networks for a particular autonomous system. Some of the IGRP key design characteristics emphasize the following:

• versatility that enables it to automatically handle indefinite, complex topologies
• flexibility for segments that have different bandwidth and delay characteristics
• scalability for functioning in very large networks

The IGRP routing protocol by default uses two metrics, bandwidth and delay. IGRP can be configured to use a combination of variables to determine a composite metric. Those variables include:

• bandwidth
• delay
• load
• reliability

command selects IGRP as a routing protocol.

The network command specifies any directly connected networks that are to be included. Note: Like RIP, all subnet masks must be the same. IGRP does not share subnetting information in routing updates.

The show ip protocol command displays parameters, filters, and network information about all of the routing protocol(s) (i.e. RIP, IGRP, etc.) in use on the router. The algorithm used to calculate the routing metric for IGRP is shown in this display. It defines the value of the K1-K5 metrics and the maximum hop count. The metric K1 represents bandwidth and the metric K3 represents delay. By default the values of the metrics K1 and K3 are set to 1. K2,K4 and K5 metric values are set to 0.

The show ip interfaces command displays the status and global parameters associated with all IP interfaces. The Cisco IOS software automatically enters a directly-connected route in the routing table if the interface is one through which software can send and receive packets. Such an interface is marked up. If the interface is unusable, it is removed from the routing table. Removing the entry allows the use of backup routes, if they exist.

Use caution when using debug commands. Debug commands are processor intensive and can decrease network performance or cause loss of connectivity. Use only during times of low network usage. Disable the command when finished by using the command, no debug ip rip or no debug all.

• Initially, a router must refer to entries about networks or subnets that are directly connected.
• Default routers learn paths to destinations three different ways:
• Static routes
• Default routes
• Dynamic routes
• The ip route command sets up a static route.
• The ip default-network command establishes a default route.
• Routers can be configured to use one or more IP routing protocols, such as RIP and IGRP.

Lab 12.1.5 Static routes

Estimated time: 30 min.

Objectives:

Prior to starting this lab you will need to connect a PC workstation (with the HyperTerminal program loaded) to a router using the router's console interface with a roll-over (console) cable. All lab work is done through the HyperTerminal program that is configured to connect to the router. You may want to review Chapter 18 in the Cisco Networking Academy First-Year Companion Guide and review semester 2 online curriculum Chapter 12 prior to starting this lab. Work individually or in teams. Be familiar with the following command:

• Enable 
• Show arp 
• Show startup-config 
• Configure terminal 
• IP route
• Show running-config 
• copy 
• Ping

Resources Required:

• PC with monitor, keyboard, mouse, power cords, etc. 
• Windows operating system (Win 95, 98, NT or 2000) installed on PC 
• HyperTerminal program configured for router console connection 
• PC connected to the router console port with a roll-over cable

Step 1 – Login to router.

Explanation: Connect to the router and login.  Enter the password cisco if prompted.  

Step 2 – Test layer 3 (network) connectivity.

Task: Enter ping xxx.xxx.xxx.xxx
Explanation: xxx.xxx.xxx.xxx is an IP address of one of your neighboring routers. 

1. Did the router’s interface respond with a successful ping?

 

Step 3 – Enter privileged mode.

Task:
         a. Enter enable at the command prompt.    
         b. Enter the password of class.
Explanation: You use the enable command to enter privileged EXEC mode.  

Step 4 – Show the backup configuration file.

Task: Enter show startup-config (abbrev. show start) at the router prompt.
Explanation: The router will display information on the backup configuration file stored in NVRAM.

2. What routing protocols or static routes are defined, if any?

 

Step 5 – Enter global configuration mode.

Task: Enter configure terminal (abbrev.  config t) at the router prompt.
Explanation: To configure the router you must enter the global configuration mode.  Notice how the router has changed after this command.

          3.  What does the router prompt look like?

Step 6 – Enter help facility.

Task: Enter IP route ? command at the router prompt.
Explanation: The router will respond with the description available for IP route. 

    4.   What was the router’s response?

Step 7 – Enter the help facility.

Task: Enter IP route xxx.xxx.xxx.xxx ?  at the router prompt.
Explanation: xxx.xxx.xxx.xxx is the network address for which you want a static route. 

    5.   What was the router's response?

Step 8 - Enter the help facility.

Task: Enter IP route xxx.xxx.xxx.xxx yyy.yyy.yyy.yyy at the router prompt.
Explanation: xxx.xxx.xxx.xxx. is the network address of the destination network and yyy.yyy.yyy.yyy is the subnet mask of the destination network.

          6. What was the router's response?       

Step 9 - Enter a static route.

Task: Enter IP route xxx.xxx.xxx.xxx yyy.yyy.yyy.yyy zzz.zzz.zzz.zzz at the router prompt.
Explanation: xxx.xxx.xxx.xxx. is the network address of the destination network and yyy.yyy.yyy.yyy is the subnet mask of the destination network. zzz.zzz.zzz.zzz is the IP address of the direct neighbor interface.

Step 10 - Exit the router global configuration mode.

Task: Enter exit at the router prompt.
Explanation: The router will exit the global configuration mode.

Step 11 - Show the running configuration.

Task: Enter show running-config at the router prompt.
Explanation: The router will show the active configuration file.

Task: Enter copy running-config startup-config at the router prompt.
Explanation: This command will permanently write the configuration change to memory.

Step 13 - Test the static route with the ping command.

Task: Enter ping xxx.xxx.xxx.xxx at the router prompt.
Explanation: xxx.xxx.xxx.xxx. is the neighboring router to which you setup a static route.

Lab 12.3.5 Rip routing

Estimated time: 45 min.

Objectives:

Prior to starting the lab the teacher will have to login to each router and delete all router RIP and static route entries from all of the routers. You will need to connect a PC workstation (with the HyperTerminal program loaded) to a router using the router's console interface with a roll-over (console) cable. All lab work is done through the HyperTerminal program that is configured to connect to the router. You may want to review Chapter 18 in the Cisco Networking Academy First-Year Companion Guide and review Semester 1 on-line chapter 12 prior to starting this lab. Work individually or in teams. Be familiar with the following commands:

• Enable 
• Show IP route
• Show startup-config 
• Configure terminal 
• Network 
• Show running-config
• Copy
• Show IP protocols
• Router RIP

Resources Required:

• PC with monitor, keyboard, mouse, power cords, etc. 
• Windows operating system (Win 95, 98, NT or 2000) installed on PC 
• HyperTerminal program configured for router console connection 
• PC connected to the router console port with a roll-over cable 

Step 1 – Login to the router.

Explanation: Connect to the router and login.  Enter the password cisco if prompted.

Step 2 - Test layer 3 connectivity. 

Task: Enter ping xxx.xxx.xxx.xxx 
Explanation: Ping all interfaces on your router and direct neighboring routers.

          1. Did all interfaces respond with a successful ping? 

            

Step 3 - View the routing table. 

Task: Enter show IP route at the router prompt. 
Explanation: The router will respond with its routing table.

          2. Is there any routing protocol defined?

           

Step 4 - Enter privileged mode. 

Task:   
         a. Enter enable at the command prompt.   
         b. Enter the password of class 
Explanation: You use the enable command to enter privileged EXEC mode.

Step 5 - Show information about the active configuration file. 

Task: Enter show running-config at the router prompt. 
Explanation: The router will display information on the active configuration file.

          3. Are there any static routes defined?

           

Step 6 - Enter global configuration mode.

Task: Enter configure terminal at the router prompt. 
Explanation: To configure the router you must enter the global configuration mode. Notice how the router prompt has changed after this command.

          4. What does the router prompt look like?

           

Step 7 - Enable RIP as your routing protocol. 

Task: Enter router RIP command at the router prompt. 
Explanation: This will enable RIP on the router.

          5. What changed in the router prompt?

           

Step 8 - Enable RIP routing on a particular IP network.

Task: Enter network xxx.xxx.xxx.xxx at the router prompt.
Explanation: xxx.xxx.xxx.xxx is the network address on which you want to enable RIP on.

Step 9 - Enable RIP routing on a particular IP network. 

Task: Repeat step 8 for all the networks directly connected to the router.

Step 10 - Exit router configuration mode. 

Task: Enter exit at the router prompt.
Explanation: The router will exit out of router configuration mode and you will be in global configuration mode.

Step 11 - Exit the router global configuration mode. 

Task: Enter exit at the router prompt. 
Explanation: The router will exit the global configuration mode.

Step 12 - Show the running configuration. 

Task: Enter show running-config at the router prompt.
Explanation: The router will show the active configuration file.

          6. Is the router RIP protocol turned on and advertising the networks you defined? 

           

Step 13 - Copy the active configuration to the backup configuration. 

Task: Enter copy running-config startup-config at the router prompt. 
Explanation: This command will permanently write the configuration change to memory.

           7. What does this command do? 

            

Step 14 - View the IP protocols.

Task: Enter show IP protocols at the router prompt. 
Explanation: The router will display values about routing timers and network information associated with the entire router.

          8. When is the next update due?
 
                

Step 15 - View the routing table. 

Task: Enter show IP route at the router prompt. 
Explanation: The router will display its routing table.

          9. How many routes were discovered by RIP?

           

Step 16 - Display the status and global parameters.

Task: Enter show IP interface at the router prompt. 
Explanation: The router displays the status and global parameters associated with an interface.

         10. What information did you receive from this command?

           

Step 17 - Display RIP routing updates as they are sent and received.

Task: Enter debug IP RIP at the command prompt.
Explanation: This command allows you to display RIP routing updates as they are sent and received.

          11.What important information did you receive from this command?

           

Step 18 - Turn off debug for RIP.

Task: Enter no debug IP RIP at the router prompt.
Explanation: This command will turn off the debugging for RIP.

Step 19 - Exit the router.

Lab 12.5.1 Rip convergence challenge

Estimated time: 60 min.

Objectives:

Tools / Preparation:

Prior to starting this lab you will need to have the equipment for the standard 5-router lab available (routers, hubs, switches, cables, etc.). The routers should be pre-configured by the instructor or lab assistant with the correct IP interface settings etc. RIP should be enabled on all routers. The workstations should also be pre-configured to have the correct IP address settings prior to starting the lab. The routers, hubs and workstations should be labeled.

Work in teams of 3 or more. Before beginning this lab you may want to review Chapter 18 in the Cisco Networking Academy First-Year Companion Guide and Semester 2 On-line Chapter 12.

Resources Required:

• 5 PC workstations (min.) with Windows operating system and HyperTerminal installed. 
• 5 Cisco Routers (model 1600 series or 2500 series with IOS 11.2 or later). 
• 4 Ethernet hubs (10BASE-T with 4 to 8 ports).
• One Ethernet switch (Cisco Catalyst 1900 or comparable).
• 5 serial console cables to connect workstation to router console port (with RJ-45 to DB9  converters).
• 3 Sets of V.35 WAN serial cables (DTE male/ DCE female) to connect from router to router.
• CAT5 Ethernet Cables wired straight through to connect routers and workstations to hubs and switches.
• AUI (DB15) to RJ-45 Ethernet transceivers (Quantity depends on the number of routers with AUI ports) to convert router AUI interfaces to 10BASE-T RJ-45.

Step 1 - Show ip route.

Verify that RIP is enabled and there are no static routes on any of the routers. If there are static routes then remove them with the no IP route xxx.xxx.xxx.xxx command in global config mode.

Step 2 - Enable debugging on Lab-D.

When you use the command debug ip rip you will be able to see all routing updates the router is receiving and sending. Turn on debugging on Lab-D.

Step 3 - Shut down the serial 1 interface on Lab-B.

Shutdown the serial 1 interface on Lab-B with the shutdown command. Watch the debugging information on Lab-D and issue the show ip route command there.

1. Has the output from the command show ip route changed from when you issued the command in step1?
    
   
2. Which networks are inaccessible?
    

Step 4 - Converged network.

After about 5 minutes issue the show ip route command on Lab-D.

Step 5 - Enter static routes.

Bring Lab-B's serial 1 interface back up. Then enter static routes for all five routers leaving RIP enabled. Issue the show ip route command. Your output from the show ip route command should look like this: Note that there are no R-RIP entries in the routing table.

Lab-D#show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default U - per-user static route, o - ODR Gateway of last resort is not set  C 204.204.7.0/24 is directly connected, Serial1  S 223.8.151.0/24 [1/0] via 204.204.7.1  S 201.100.11.0/24 [1/0] via 204.204.7.1  S 219.17.100.0/24 [1/0] via 204.204.7.1  S 192.5.5.0/24 [1/0] via 204.204.7.1 S 199.6.13.0/24 [1/0] via 204.204.7.1  S 205.7.5.0/24 [1/0] via 204.204.7.1  C 210.93.105.0/24 is directly connected, Ethernet0

Step 6 - Shut down the serial 1 interface on Lab-B.

After you shutdown the serial 1 interface on Lab-B watch the debugging information on Lab-D.   

Step 7 – Turn off debugging on Lab-D.

Turn off debugging on Lab-D using the undebug all command.

Lab 12.5.2 Routing loops setup challenge

Estimated time: 30 min.

Objectives:

• Configure a WAN connection between Lab-A and Lab-E.
• Demonstrate your ability to configure Serial interfaces.

In this lab you will setup a WAN connection between Lab-A and Lab-E to create alternate paths in the standard router lab setup. Using a set of WAN serial cables, connect Lab-A Serial 1 to Lab-E Serial 0. Remember to set the clock rate on the DCE side of the cable (Lab-E's Serial 0 interface).

Prior to starting this lab you will need to have the equipment for the standard 5-router lab available (routers, hubs, switches, cables, etc.). The routers should be pre-configured by the instructor or lab assistant with the correct IP interface settings etc. The workstations should also be pre-configured to have the correct IP address settings prior to starting the lab. The routers, hubs and workstations should be labeled.

This lab assumes that the equipment (routers, hubs, workstations, etc.) are assembled and connected in the standard lab topology. Work in teams of 3 or more. You may want to review Chapter 11 in the Cisco Networking Academy First-Year Companion Guide and review Semester 2 On-line Chapter 12.

Resources Required:

• 5 PC workstations (min.) with Windows operating system and HyperTerminal installed. 
• 5 Cisco Routers (model 1600 series or 2500 series with IOS 11.2 or later).
• 4 Ethernet hubs (10BASE-T with 4 to 8 ports). 
• One Ethernet switch (Cisco Catalyst 1900 or comparable).
• 5 serial console cables to connect workstation to router console port (with RJ-45 to DB9 converters).
• 4 Sets of V.35 WAN serial cables (DTE male/ DCE female) to connect from router to router. 
• CAT5 Ethernet Cables wired straight through to connect routers and workstations to hubs and switches.
• AUI (DB15) to RJ-45 Ethernet transceivers (Quantity depends on the number of routers with AUI ports)
  to convert router AUI interfaces to 10BASE-T RJ-45.
  

Step 1 - Verify that all physical connections are correct.

Review the standard semester 2 Lab diagram in the overview section of this lab. You will add a 4th set of V.35 WAN serial cables (DTE male/ DCE female) to connect from router Lab-A interface S1 to router Lab-E interface S0.

Step 2 - Configure Lab-A serial 1 interface.

Login to the router and enter the interface configuration mode. Configure interface serial 1 with the following information (this is a new class C IP address): 
IP address 220.68.33.2 
Subnet Mask 255.255.255.0
Bandwidth of 56

Step 3 - Configure IP host and RIP networks.

After you have finished the configuration for the interface, you will need to add the 220.68.33.0 network with the network command to all 5 routers. Also, add the new IP address to the host table entry for routers Lab-A and Lab-E for name resolution to all routers.

Step 4 - Configure Lab-E serial 0 interface. 

Repeat steps 2 and 3 for Lab-E interface serial 0 with the following information: 
IP address 220.68.33.1 
Subnet Mask 255.255.255.0 
Clock rate 56000 
Bandwidth of 56

Step 5 - Test your setup. 

When you have configured Lab-A's and Lab-E's interfaces, check off the items in the list:

• Ping from all routers to 220.68.33.1

• Ping from all routers to 220.68.2 2.2

• Ping from all Workstations to 220.68.33.1

• Ping from all Workstations to 220.68.33.2

• Telnet from Lab-C to 220.68.33.1

• Telnet from Lab-C to 220.68.33.2

• Telnet from Workstation to 220.68.33.1

• Telnet from Workstation to 220.68.33.2  

Step 6 - Troubleshooting. 

If you were not able to finish step 5 then use your troubleshooting skills learned in previous labs to correct the problem. After you have successfully finished step 5 save the running configuration to the startup configuration for all routers. 

Lab 12.5.3  Preventing routing loops

Estimated time: 45 min.

Objectives:

Prior to starting this lab you will need to have the equipment for the standard 5-router lab available. The routers and workstations should be pre-configured by the instructor or lab assistant with the correct IP settings prior to starting the lab. Before beginning this lab you may want to review Chapters 11 in the Cisco Networking Academy First-Year Companion Guide and Semester 2 On-line Chapter 12.

Resources Required:

• 5 PC workstations (min.) with Windows operating system and HyperTerminal installed.
• 5 Cisco Routers (model 1600 series or 2500 series with IOS 11.2 or later). 
• 4 Ethernet hubs (10BASE-T with 4 to 8 ports).
• One Ethernet switch (Cisco Catalyst 1900 or comparable).
• 5 serial console cables to connect workstation to router console port (with RJ-45 to DB9 converters).
• 4 Sets of V.35 WAN serial cables (DTE male/ DCE female) to connect from router to router.
• CAT5 Ethernet Cables wired straight through to connect routers and workstations to hubs and switches. 
• AUI (DB15) to RJ-45 Ethernet transceivers (Quantity depends on the number of routers with AUI ports) to convert router AUI interfaces to 10BASE-T RJ-45.

Step 1 – Turn on debugging.

Working with router Lab-C, turn on debugging with the debug ip rip command.  

Step 2 – Shutdown Lab-A’s Ethernet 0 interface.

Shutdown Lab-A’s Ethernet 0 interface.  From Lab-C, watch the routing information and use the show ip route command to see how many routing updates it takes to flush out Lab-A’s Ethernet 0 network. 

1. How many updates did it take to converge?

Step 3 – Enable Lab-A’s Ethernet 0 interface.

On Lab-A bring Ethernet 0 back up and allow enough time for the network to converge. 

Step 4 – Configure default metric, timers basic and split-horizon on Lab-C.

There are other timers that can be modified to help avoid routing loops.  This lab focuses on hop count.  Change the RIP maximum hop count on router Lab-C to 10 (the default is 16), adjust the routing timers and split horizon using the following commands:

Lab-C#conf t
Lab-C(config)#router rip
Lab-C(config-router)#default-metric 10
Lab-C(config-router)#timers basic 30 60 150 30
Lab-C(config-router)#exit
Lab-C(config)#int s0
Lab-C(config-if)#ip split-horizon
Lab-C(config-if)#int s1
Lab-C(config-if)#ip split-horizon
Lab-C(config-if)#^Z 
Lab-C#

Step 5 - Shutdown Lab-A's Ethernet 0 interface.

Shutdown Lab-A's Ethernet 0 interface. From Lab-C, watch the routing information and use the show ip route command to see how many routing updates it takes to flush out Lab-A's Ethernet 0 network.

2. How many updates did it take to converge?

3. Compare question 1 and 2 and explain why the network converged faster after changing the default  metric, timers and split horizon.

Throughout this entire semester you have been using the same basic configuration for your labs and simulations. For these troubleshooting labs, you can refer to this configuration and imagine what could go wrong with it, in terms of the OSI layers. - Examples of problems in each layer might include:

• Layer 1 - incorrect cable used
• Layer 2 - interface not configured for Ethernet
• Layer 3 - subnet mask is incorrect

• improperly configured serial interfaces
• improperly configured Ethernet interfaces
• improper encapsulation set (HDLC is default for serial interfaces)
• improper clockrate settings on serial interfaces

• routing protocol not enabled
• wrong routing protocol enabled
• incorrect IP addresses
• incorrect Subnet Masks
• incorrect DNS to IP bindings

Lab 13.1.6 Troubleshooting 5-router network - Overview

Estimated time: 30 min.

Objectives:

• Troubleshoot problems in the 5-router lab network 
• Document the problems found and corrective action taken 
• Prepare for Part B of the Final Exam (Router Lab Troubleshooting)

For this lab, your instructor has created/introduced multiple problems in the network. You have a limited amount of time in which to find and solve the problems so that you can get the entire network up and running.

The tools that you may use for the hardware are in your tool kit.  The tools that you may use for the software (IOS) include ping, trace ip route, telnet, and show arp. You may use your Engineering Journal and any Web-based resources (including the curriculum) that are available. As you discover the problems you will document them along with what you did to correct them.

Prior to starting this lab you should have the equipment for the standard 5-router lab available. All routers and workstations should be properly configured. You will be asked to leave the room and your instructor or lab assistant will introduce 3 to 5 problems into the lab setup.

Step 1 - Review the physical connections on the standard lab setup.

Review the standard semester 2 lab diagram in the overview section of this lab and check all physical devices, cables and connections. 

Step 2 - Troubleshooting induced network problems.

Basic Problem descriptions:
a) We cannot ping a host on LAB-E's network from a host on LAB-A's network.
b) We cannot telnet from one router to another router's host name
The instructor will induce multiple problems (3 to 5) into the network (see answers section) that can cause these high level symptoms. Your team will have a fixed time period (20 to 30 minutes) to correct the problems. You may use your journals and toolkits to troubleshoot the problems.

Step 3 - Document the problems discovered.

Write down the problems as you encounter them and then indicate what you did to correct them. When you are able to ping from a Lab-A workstation to a Lab-E workstation and telnet from one router to another router's host name, have the instructor verify that you have corrected all problems.

Prob. #	Problem discovered	Solution	Instructor verification
1
2
3
4
5