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CCNP BSCI Exam: Introduction to the Intermediate System-to-Intermediate System (IS-IS) Protocol

Chapter Description

Review the Intermediate System-to-Intermediate System (IS-IS) technology, its structures, and protocols by examining Open System Interconnection (OSI) routing, basic IS-IS and integrated IS-IS router configuration commands, examples, and some troubleshooting guidelines.

Configuration Exercise: Configuring a Multiarea IS-IS Network

Configuration Exercises

In this book, configuration exercises are used to provide practice in configuring routers with the commands presented. If you have access to real hardware, you can try these exercises on your routers. Refer to Appendix H for a list of recommended equipment and configuration commands for the backbone routers. However, even if you don't have access to any routers, you can go through the exercises and keep a log of your own running configurations on separate sheets of paper.

Commands used and answers to the configuration exercises are provided at the end of the exercise.

In these exercises, you are in control of a pod of 3 routers; there are assumed to be 12 pods in the network. The pods are interconnected to a backbone. In most of the exercises, there is only one router in the backbone; in some cases, another router is added to the backbone. Each of the configuration exercises in this book assumes that you have completed the previous exercises on your pod.

NOTE

This configuration exercise assumes that you have completed the OSPF exercises in Chapter 4. The configuration for the backbone_r1 router for this exercise is provided in Appendix H.

In this exercise, you will configure IS-IS within your pod to the backbone_r1 router.

Objectives

In the following configuration exercise, you will do the following:

  • Configure the pxr1, pxr2, and pxr3 routers in your pod to be in a specific IS-IS area.

  • Enable IS-IS on the proper interfaces on the pxr1, pxr2, and pxr3 routers.

  • Configure the pxr2 and pxr3 routers to be Level 1 routers.

  • Configure the pxr1 router to perform route summarization.

  • Verify proper Level 1 adjacencies among the pxr1, pxr2, and pxr3 routers within your pod.

  • Verify proper Level 2 adjacencies between your pxr1 router and the backbone_r1 router.

  • Verify that the pxr1 router is advertising a default route to the pxr2 and pxr3 routers.

  • Verify which router is the designated IS router on the Ethernet link between pxr2 and pxr3.

  • Verify and change the Ethernet interface IS-IS router priority.

  • Verify proper network connectivity.

  • Use show and debug commands to verify IS-IS operations.

Visual Objective

Figure 5-24 illustrates the topology used in the network.

Figure 5-24Figure 5-24 Configuration Exercise Topology

Command List

In this exercise, you will use commands in Table 5-15. Refer to this list if you need configuration command assistance during the exercise.

Table 5-15 Configuration Exercise Command List

Command

Description

router isis

Enables IS-IS

net 00.000x.xyxy.xyxy.xyxy.00

Configures the NET

ip router isis

Enables IS-IS on the interface

is-type level-1

Configures the router as a Level 1 IS-IS router

summary-address 192.168.x.0 255.255.255.0

Configures route summarization

isis priority 63

Changes the IS-IS router priority on the Ethernet interface to influence the DR election

show clns interface s0

Displays CLNS interface status and configuration

show clns is-neighbors

Displays the IS-IS neighbor table

show isis database

Displays the IS-IS link-state database

show isis spf-log

Displays how often and why the router has run a full SPF calculation

debug isis adj-packets

Displays IS-IS adjacency-related packets

debug isis update-packets

Displays IS-IS update-related packets


Setup

To set up, do the following:

Step 1

Disable OSPF on all the routers within your pod.

Step 2

Shut the pxr1 S3 interface.


Task 1: Enabling IS-IS Within Your Pod

Complete the following steps:

Step 1

Enable IS IS on the pxr1, pxr2, and pxr3 routers within your pod.

Step 2

Configure the pxr1, pxr2, and pxr3 routers within your pod with the IS IS NETs shown in the following table.


Pod

pxr1 NET

pxr2 NET

pxr3 NET

1

00.0001.1111.1111.1111.00

00.0001.1212.1212.1212.00

00.0001.1313.1313.1313.00

2

00.0002.2121.2121.2121.00

00.0002.2222.2222.2222.00

00.0002.2323.2323.2323.00

3

00.0003.3131.3131.3131.00

00.0003.3232.3232.3232.00

00.0003.3333.3333.3333.00

4

00.0004.4141.4141.4141.00

00.0004.4242.4242.4242.00

00.0004.4343.4343.4343.00

5

00.0005.5151.5151.5151.00

00.0005.5252.5252.5252.00

00.0005.5353.5353.5353.00

6

00.0006.6161.6161.6161.00

00.0006.6262.6262.6262.00

00.0006.6363.6363.6363.00

7

00.0007.7171.7171.7171.00

00.0007.7272.7272.7272.00

00.0007.7373.7373.7373.00

8

00.0008.8181.8181.8181.00

00.0008.8282.8282.8282.00

00.0008.8383.8383.8383.00

9

00.0009.9191.9191.9191.00

00.0009.9292.9292.9292.00

00.0009.9393.9393.9393.00

10

00.0010.A1A1.A1A1.A1A1.00

00.0010.A2A2.A2A2.A2A2.00

00.0010.A3A3.A3A3.A3A3.00

11

00.0011.B1B1.B1B1.B1B1.00

00.0011.B2B2.B2B2.B2B2.00

00.0011.B3B3.B3B3.B3B3.00

12

00.0012.C1C1.C1C1.C1C1.00

00.0012.C2C2.C2C2.C2C2.00

00.0012.C3C3.C3C3.C3C3.00


 

NOTE

The backbone_r1 router is configured with a NET of 00.0013.1111.2222.3333.00.

Step 3

Enable IS IS on the interfaces specified in the following table on the pxr1, pxr2, and pxr3 routers within your pod.


Router

Interfaces on Which to Enable IS-IS

 

 

 

 

pxr1

S0

S1

S2

 

 

pxr2

S0

S1

E0

Loopback10

 

pxr3

S0

E0

Loopback11

Loopback12

Loopback13


 

NOTE

For this task, the pxr1 S3 interface is shut down.

Step 4

Display the routing table of the pxr1, pxr2, and pxr3 routers within your pod, and verify that you have full connectivity within your pod.

Step 5

Examine the pxr1 routing table and answer the following questions:

 

Does IS-IS load-balance by default?

 

What is the IS-IS routing metric based on by default?

 

Use the show clns int s0 command to determine the Level 1 and Level 2 default metric.

 

What is the default administrative distance of IS-IS routes?

Step 6

Save the current configurations of all the routers within your pod to NVRAM.


Task 2: Enabling Connectivity to the backbone_r1 Router

Complete the following steps:

Step 1

No shut the S3 interface on the pxr1 router.

Step 2

Enable IS-IS on the S3 interface on the pxr1.

Step 3

Display the routing table of the pxr1, pxr2, and pxr3 routers within your pod, and verify that you have full connectivity to the backbone_r1 router.

 

Do you see the backbone_r1 router's loopback interfaces in your routing table? (Note that you also might see routes to the other pods.)

 

Does IS-IS perform autosummarization across the network boundary by default?

 

Does IS-IS use the same default administrative distance for Level 1 and Level 2 routes?

 

Make sure that you can ping the loopback interfaces on the backbone_r1 router from the pxr1, pxr2, and pxr3 routers within your pod.

Step 4

Save the current configurations of all the routers within your pod to NVRAM.


Task 3: Changing the IS-IS Router Type

Complete the following steps:

Step 1

By default, the pxr1, pxr2, and pxr3 routers within your pod are what type of IS-IS router (Level 1, Level 2, or Level 1–2)?

 

What command can be used to determine the IS-IS router type?

Step 2

Examine the IS-IS link state database of the pxr1, pxr2, and pxr3 routers within your pod. Do you see both the Level 1 and Level 2 link-state database on all the routers?

 

In the link-state database, which link-state packet (LSP) is identified with an asterisk?

 

Examine the routing table of the pxr2 and pxr3 routers within your pod. Do you see both the Level 1 and Level 2 routes?

Step 3

Configure the pxr2 and pxr3 routers within your pod to be Level 1 IS-IS routers.

Step 4

What are the advantages of configuring the pxr2 and pxr3 routers within your pod to be Level 1 IS-IS routers?

Step 5

Re-examine the link-state database of the pxr2 and pxr3 routers within your pod. Do the pxr2 and pxr3 routers contain only the Level 1 link-state database now?

Step 6

Re-examine the routing table of the pxr2 and pxr3 routers now. What are the differences after they became Level 1–only IS-IS routers?

Step 7

In the pxr2 and pxr3 routing tables, do you see a default route through the pxr1 router?

Step 8

From the pxr2 or pxr3 routers, can you still ping the backbone_r1 router's loopback interfaces?

Step 9

Save the current configurations of all the routers within your pod to NVRAM.


Task 4: Configure Route Summarization

Complete the following steps:

Step 1

From pxr3, telnet to the backbone_r2 router using the password cisco.

Step 2

Display the routing table of the backbone_r1 router. Do you see your 192.168.x.y/28 and 172.26.x.y/28 subnets?

Step 3

Exit the telnet to the backbone_r1 router.

Step 4

Configure the Level 1–2 router within your pod to perform route summarization. Summarize the 192.168.x.y/28 and 172.26.x.y/28 subnets within your pod to 192.168.x.0/24 and 172.26.x.0/24 (where x is your pod number).

Step 5

Telnet to the backbone_r1 router.

Step 6

Re-examine the routing table of the backbone_r1 router. Do you see your summarized routes?

Step 7

From the backbone_r1 router, can you ping all the interfaces within your pod?

Step 8

Exit the telnet to the backbone_r1 router.

Step 9

Save the current configurations of all the routers within your pod to NVRAM.


Task 5: Using IS-IS show and debug Commands

Complete the following steps:

Step 1

At the pxr2 router, enable the debug isis adj-packets command and observe the debug output.

 

What type of hello is pxr2 sending to pxr3 over the Ethernet interface?

Step 2

Shut the pxr2 E0 interface and observe the debug output.

Step 3

No shut the pxr2 E0 interface and observe the debug output. From the debug output, determine which router (pxr2 or pxr3) is elected as the DR.

NOTE

The correct term in IS-IS is DIS, not DR. However, the debug output on the router uses the term DR, so we will also use the term DR in this task.

In the debug output, you should see something similar to the output shown in Example 5-29 if pxr3 is the DR.


Example 5-29 debug isis adj-packets Command Output from Router pxr2 If Router pxr3 Is the DR

02:23:12: ISIS-Adj: Adjacency state goes to Up
02:23:12: ISIS-Adj: Run level 1 DR election for Ethernet0
02:23:12: ISIS-Adj: New level 1 DR 3333.3333.3333 on Ethernet0
pxr2

Or, in the debug output, you should see something similar to the output shown in Example 5-30 if pxr2 is the DR.


Example 5-30 debug isis adj-packets Command Output from Router pxr2 If Router pxr2 Is the DR

05:19:43: ISIS-Adj: Run level 1 DR election for Ethernet0
05:19:43: ISIS-Adj: No change (it's us)
pxr2#

 

What determines who will be elected as the DR on the Ethernet?

Step 4

Disable debug isis adj-packets at the pxr2 router.

Step 5

At the DR (as determined from Step 3), enter the show clns int e0 command. What is the default IS-IS router priority set to?

Step 6

At the DR (as determined from Step 3), change the E0 interface IS-IS router priority to 63.

Step 7

At the DR (as determined from Step 3), enter the show clns int e0 command again and verify that the DR is now changed to the other router.

 

The Circuit ID field in the show clns int e0 output identifies which router is the DR. Example 5-31 shows the output of this command on the pxr3 router. In this example, the DR is the pxr2 router and the pxr3 router has an IS-IS priority of 63.


Example 5-31 show clns Command Output from Router pxr3 If Router pxr2 Is the DR

pxr3#show clns int e0
Ethernet0 is up, line protocol is up
Checksums enabled, MTU 1497, Encapsulation SAP
ERPDUs enabled, min. interval 10 msec.
RDPDUs enabled, min. interval 100 msec., Addr Mask enabled
Congestion Experienced bit set at 4 packets
CLNS fast switching enabled
CLNS SSE switching disabled
DEC compatibility mode OFF for this interface
Next ESH/ISH in 21 seconds
Routing Protocol: IS-IS
Circuit Type: level-1-2
Interface number 0x1, local circuit ID 0x1
Level-1 Metric: 10, Priority: 63, Circuit ID: 2222.2222.2222.01
Number of active level-1 adjacencies: 1
Next IS-IS LAN Level-1 HELLO in 8 seconds

Step 8

At the pxr2 router, enable the debug isis update-packets command. Shut and no shut the E0 interface on the pxr2 router and observe the debug output.

Step 9

Disable debug isis update-packets at the pxr2 router.

Step 10

At the pxr2 router, use the proper show command to verify how often and why the router has run a full SPF calculation.

Step 11

At the pxr2 router, use the proper show command to examine the IS-IS neighbor table. How many entries do you see? Are they all Level 1 adjacency?

Step 12

At the pxr1 router, use the proper show command to examine the IS-IS neighbor table. How many entries do you see? Do you see both Level 2 and Level 1 adjacencies?

Step 13

Display the running configuration of the pxr1 router. Is clns routing enabled by default?

Step 14

Save the current configurations of all the routers within your pod to NVRAM.


Completion Criteria

You have successfully completed this configuration exercise if you correctly supplied the commands required to configure IS-IS within your pod and to the backbone_r1 router, and if you were able to correctly answer the questions in the exercise. At the end of this exercise, all the routers should have full connectivity to each other. All routers will be running the IS-IS routing protocol.

8. Answers to Configuration Exercise: Configuring a Multiarea IS-IS Network | Next Section Previous Section