CCNP Route Lab 3-6, OSPF Troubleshooting Lab

CCNP Route Lab 3-6, OSPF Troubleshooting Lab

Topology

ccnp-route-lab-ospf-troubleshooting-lab

Objectives

  • Troubleshoot OSPF operation and configuration.

Background
In this lab, you troubleshoot existing configurations to get a working topology. Some of these configurations are correct, and some are intentionally wrong. Your goal is to use troubleshooting techniques to fix anything in the scenario that prevents full IP connectivity. Full IP connectivity means every address in the scenario should be reachable from every router. If you do not know where to start, try pinging remote addresses and see which ones are reachable (either manually performing pings or using a Tcl script).

Note: This lab uses Cisco 1841 routers with Cisco IOS Release 12.4(24)T1 and the Advanced IP Services image c1841 -advipservicesk9-mz.124-24.T1 .bin. You can use other routers (such as a 2801 or 2811) and Cisco IOS Software versions if they have comparable capabilities and features. Depending on the router model and Cisco IOS Software version, the commands available and output produced might vary from what is shown in this lab.

Required Resources

  • 4 routers (Cisco 1841 with Cisco IOS Release 12.4(24)T1 Advanced IP Services or comparable)
  • Serial and console cables

Requirements

  • Cut and paste the initial configurations from this lab into the respective routers.
  • Use the IP addressing scheme shown in the diagram.
  • All routers must participate in OSPF.
  • All interfaces must be in the OSPF areas shown in the diagram.
  • Do not use static routes, default routes, or other routing protocols.
  • All IP addresses in the topology must be reachable from all routers.
  • The OSPF network type for the link between R2 and R3 is nonbroadcast.

Initial Configurations

Router R1

Router R2

Router R3

Router R4

Notes:
__________________________________________________________________________________
Router Interface Summary Table

Router Interface Summary
Router Model Ethernet Interface
#1
Ethernet Interface
#2
Serial Interface
#1
Serial Interface
#2
1700 Fast Ethernet 0
(Fa0)
Fast Ethernet 1
(Fa1)
Serial 0 (S0) Serial 0/0/1
(S0/0/1)
1800 Fast Ethernet 0/0
(Fa0/0)
Fast Ethernet 0/1
(Fa0/1)
Serial 0/0/0
(S0/0/0)
Serial 0/0/1
(S0/0/1)
2600 Fast Ethernet 0/0
(Fa0/0)
Fast Ethernet 0/1
(Fa0/1)
Serial 0/0 (S0/0) Serial 0/1 (S0/1)
2800 Fast Ethernet 0/0
(Fa0/0)
Fast Ethernet 0/1
(Fa0/1)
Serial 0/0/0
(S0/0/0)
Serial 0/0/1
(S0/0/1)
Note: To find out how the router is configured, look at the interfaces to identify the type of router and how many interfaces the router has. Rather than list all combinations of configurations for each router class, this table includes identifiers for the possible combinations of Ethernet and serial interfaces in the device. The table does not include any other type of interface, even though a specific router might contain one. For example, for an ISDN BRI interface, the string in parenthesis is the legal abbreviation that can be used in Cisco IOS commands to represent the interface.

OSPF Troubleshooting Lab Answer Key – Instructor Version

Getting Started

This answer key goes over how to troubleshoot the various problems in the lab. One logical place to start is to make sure that all adjacencies are up and that all remote addresses are reachable.

Problem 1: R1 -R2 Adjacency Not Forming

When troubleshooting OSPF, one place to start is to see which adjacencies are formed and which are not using the show ip ospf neighbor command. The adjacency between R1 and R2 is not there, so you can start by looking into this adjacency. To display the interfaces on which OSPF is running and how they are configured, use the show ip ospf interface command.

As you can tell from the output, OSPF is not running on the R1 Serial0/0/0 interface. This means that you
should examine two places: the interface itself and the OSPF configuration.

The interface looks fine. The IP address matches the diagram, the clock rate is configured correctly, and the interface is not shut down. What about the OSPF configuration?

It looks almost correct. However, the network statement is a /32 mask on the wrong IP address (R2’s address). You must change this either by putting in the correct address or just giving it a /24 mask.

The adjacency should come up shortly after this. Now the show ip ospf interface command yields the correct output.

Problem 2: R2-R3 Adjacency Not Forming
Using the same problem-finding technique as before, you can see that the adjacency between R2 and R3 has also not formed. Using the show ip ospf interface command, you can see that both routers are running OSPF on the link.

Remember that one of the requirements for this lab was to configure the network as a nonbroadcast OSPF network. When using nonbroadcast networks, you must statically set up neighbor statements because the hello packets will not be multicast. Check the neighbor statements on both routers.

It appears that no neighbor statements are configured. For a situation like this, you could configure the statements on either router because only one needs to be configured to initiate an adjacency. Here, the neighbor statement is configured on R2.

You should see a message logged about the adjacency coming up.

Problem 3: The R4 Loopback Address Not Advertised
After the previous problems are resolved, all adjacencies should be up and working properly. When checking for full connectivity, however, you see that the R4 loopback address is unreachable from remote routers.Referring to the topology and with your knowledge of OSPF, you know that for a remote area to be reachable without a router touching the backbone, it must have a virtual link to extend the backbone area to it. You know that the problem is not the neighbor adjacency between R3 and R4 because the output of the show ip ospf neighbor command has an adjacency up.

As suspected, the virtual link between the two routers is down. One important aspect of a virtual link configuration is that the target must be the router ID of the remote routers, not their IP address on the link.Get both router IDs using the show ip protocols or show ip ospf command (each command is shown below with the IDs highlighted).

Referring back to the output of the show ip ospf virtual-links command, you can see that R4 is misconfigured with R3’s link address as the target, rather than R3’s router ID. This can be verified in the configuration.

After you correct the problem, you should see the virtual link come up.

You should now have full IP connectivity.

Tcl Verification Script

Final Device Configurations

Router R1

Router R2

Router R3

Router R4

More Resources

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