CCNP Route Lab 3-6, OSPF Troubleshooting Lab
Topology
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
hostname R1 ! interface Loopback0 ip address 172. 16.1.1 255.255.255.0 ! interface Serial0/0/0 ip address 172.16.12.1 255.255.255.0 clock rate 64000 bandwidth 64 no shutdown ! router ospf 1 network 172.16.1.0 0.0.0.255 area 0 network 172.16.12.2 0.0.0.0 area 0 end
Router R2
hostname R2 ! interface Loopback0 ip address 172.16.2.1 255.255.255.0 ! interface Serial0/0/0 ip address 172.16.12.2 255.255.255.0 bandwidth 64 no shutdown ! interface Serial0/0/1 ip address 172.16.23.2 255.255.255.0 ip ospf network non-broadcast clock rate 64000 bandwidth 64 no shutdown ! router ospf 1 network 172.16.2.0 0.0.0.255 area 0 network 172.16.12.0 0.0.0.255 area 0 network 172.16.23.0 0.0.0.255 area 0 end
Router R3
hostname R3 ! interface Loopback0 ip address 172.16.3.1 255.255.255.0 ! interface Serial0/0/1 ip address 172.16.23.3 255.255.255.0 ip ospf network non-broadcast bandwidth 64 no shutdown ! interface Serial0/1/0 ip address 172.16.34.3 255.255.255.0 clock rate 64000 bandwidth 64 no shutdown ! router ospf 1 area 34 virtual-link 172.16.4.1 network 172.16.3.0 0.0.0.255 area 34 network 172.16.23.0 0.0.0.255 area 0 network 172.16.34.0 0.0.0.255 area 34 end
Router R4
hostname R4 ! interface Loopback0 ip address 172.16.4.1 255.255.255.0 ! interface Serial0/0/0 ip address 172.16.34.4 255.255.255.0 bandwidth 64 no shutdown ! router ospf 1 area 34 virtual-link 172.16.34.3 network 172.16.4.0 0.0.0.255 area 40 network 172.16.34.0 0.0.0.255 area 34 end
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.
R1# show ip ospf interface Loopback0 is up, line protocol is up Internet Address 172.16.1.1/24, Area 0 Process ID 1, Router ID 172.16.1.1, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host R2# show ip ospf interface Serial0/0/1 is up, line protocol is up Internet Address 172.16.23.2/24, Area 0 Process ID 1, Router ID 172.16.2.1, Network Type NON_BROADCAST, Cost: 1562 Transmit Delay is 1 sec, State DR, Priority 1 Designated Router (ID) 172.16.2.1, Interface address 172.16.23.2 No backup designated router on this network Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5 oob-resync timeout 120 Hello due in 00:00:14 Supports Link-local Signaling (LLS) Index 2/2, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 0, maximum is 1 Last flood scan time is 0 msec, maximum is 4 msec Neighbor Count is 0, Adjacent neighbor count is 0 Suppress hello for 0 neighbor(s) Loopback0 is up, line protocol is up Internet Address 172.16.2. 1/24, Area 0 Process ID 1, Router ID 172.16.2.1, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host Serial0/0/0 is up, line protocol is up Internet Address 172.16.12.2/24, Area 0 Process ID 1, Router ID 172.16.2.1, Network Type POINT_TO_POINT, Cost: 1562 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:02 Supports Link-local Signaling (LLS) Index 1/1, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 0, maximum is 3 Last flood scan time is 0 msec, maximum is 4 msec Neighbor Count is 0, Adjacent neighbor count is 0 Suppress hello for 0 neighbor(s)
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.
R1# show run interface serial0/0/0 Building configuration... Current configuration : 100 bytes ! interface Serial0/0/0 ip address 172.16.12.1 255.255.255.0 no fair-queue clock rate 64000 bandwidth 64 end
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?
R1# show run | section ospf router ospf 1 log-adjacency-changes network 172.16.1.0 0.0.0.255 area 0 network 172.16.12.2 0.0.0.0 area 0
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.
R1(config)# router ospf 1 R1(config-router)# no network 172.16.12.2 0.0.0.0 area 0 R1(config-router)# network 172.16.12.0 0.0.0.255 area 0
The adjacency should come up shortly after this. Now the show ip ospf interface command yields the correct output.
R1# show ip ospf interface Serial0/0/0 is up, line protocol is up Internet Address 172.16.12.1/24, Area 0 Process ID 1, Router ID 172.16.1.1, Network Type POINT_TO_POINT, Cost: 1562 Transmit Delay is 1 sec, State POINT_TO_POINT Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:00 Supports Link-local Signaling (LLS) Cisco NSF helper support enabled IETF NSF helper support enabled Index 2/2, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 1, maximum is 1 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 172.16.2.1 Suppress hello for 0 neighbor(s) Loopback0 is up, line protocol is up Internet Address 172.16.1.1/24, Area 0 Process ID 1, Router ID 172.16.1.1, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host
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.
R2# show ip ospf interface Serial0/0/1 is up, line protocol is up Internet Address 172.16.23.2/24, Area 0 Process ID 1, Router ID 172.16.2.1, Network Type NON_BROADCAST, Cost: 1562 Transmit Delay is 1 sec, State DR, Priority 1 Designated Router (ID) 172.16.2.1, Interface address 172.16.23.2 No backup designated router on this network Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5 oob-resync timeout 120 Hello due in 00:00:04 Supports Link-local Signaling (LLS) Index 2/2, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 0, maximum is 1 Last flood scan time is 0 msec, maximum is 4 msec Neighbor Count is 0, Adjacent neighbor count is 0 Suppress hello for 0 neighbor(s) Loopback0 is up, line protocol is up Internet Address 172.16.2.1/24, Area 0 Process ID 1, Router ID 172.16.2.1, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host Serial0/0/0 is up, line protocol is up Internet Address 172.16.12.2/24, Area 0 Process ID 1, Router ID 172.16.2.1, Network Type POINT_TO_POINT, Cost: 1562 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:03 Supports Link-local Signaling (LLS) Index 1/1, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 1, maximum is 3 Last flood scan time is 0 msec, maximum is 4 msec Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 172.16.1.1 Suppress hello for 0 neighbor(s) R3# show ip ospf interface OSPF_VL1 is down, line protocol is down Internet Address 0.0.0.0/0, Area 0 Process ID 1, Router ID 172.16.3.1, Network Type VIRTUAL_LINK, Cost: 65535 Configured as demand circuit. Run as demand circuit. DoNotAge LSA allowed. Transmit Delay is 1 sec, State DOWN, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Serial0/0/1 is up, line protocol is up Internet Address 172.16.23.3/24, Area 0 Process ID 1, Router ID 172.16.3.1, Network Type NON_BROADCAST, Cost: 1562 Transmit Delay is 1 sec, State DR, Priority 1 Designated Router (ID) 172.16.3.1, Interface address 172.16.23.3 No backup designated router on this network Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5 oob-resync timeout 120 Hello due in 00:00:01 Supports Link-local Signaling (LLS) Index 1/2, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 3, maximum is 3 Last flood scan time is 0 msec, maximum is 4 msec Neighbor Count is 0, Adjacent neighbor count is 0 Suppress hello for 0 neighbor(s) Serial0/1/0 is up, line protocol is up Internet Address 172.16.34.3/24, Area 34 Process ID 1, Router ID 172.16.3.1, Network Type POINT_TO_POINT, Cost: 1562 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:02 Supports Link-local Signaling (LLS) Index 2/3, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 1, maximum is 3 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 172.16.4.1 Suppress hello for 0 neighbor(s) Loopback0 is up, line protocol is up Internet Address 172.16.3.1/24, Area 34 Process ID 1, Router ID 172.16.3.1, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host
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.
R2# show run | section ospf router ospf 1 log-adjacency-changes network 172.16.2.0 0.0.0.255 area 0 network 172.16.12.0 0.0.0.255 area 0 network 172.16.23.0 0.0.0.255 area 0 R3# show run | section ospf router ospf 1 log-adjacency-changes area 34 virtual-link 172.16.4.1 network 172.16.3.0 0.0.0.255 area 34 network 172.16.23.0 0.0.0.255 area 0 network 172.16.34.0 0.0.0.255 area 34
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.
R2(config)# router ospf 1 R2(config-router)# neighbor 172.16.23.3
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.
R4# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 172.16.3.1 0 FULL/ - router os 1 00:00:33 172.16.34.3 Serial0/0/0 To verify the virtual link status, use the show ip ospf virtual-links command. R3# show ip ospf virtual-links Virtual Link OSPF_VL1 to router 172.16.4.1 is down Run as demand circuit DoNotAge LSA allowed. Transit area 34, Cost of using 65535 Transmit Delay is 1 sec, State DOWN, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 R4# show ip ospf virtual-links Virtual Link OSPF_VL1 to router 172.16.34.3 is down Run as demand circuit DoNotAge LSA allowed. Transit area 34, Cost of using 65535 Transmit Delay is 1 sec, State DOWN, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
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).
R3# show ip protocols Routing Protocol is "ospf 1" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Router ID 172.16.3.1 It is an area border router Number of areas in this router is 2. 2 normal 0 stub 0 nssa Maximum path: 4 Routing for Networks: 172.16.3.0 0.0.0.255 area 34 172.16.23.0 0.0.0.255 area 0 172.16.34.0 0.0.0.255 area 34 Reference bandwidth unit is 100 mbps Routing Information Sources: Gateway Distance Last Update 172.16.4.1 110 17:52:05 172.16.1.1 110 02:00:02 172.16.2.1 110 02:00:02 Distance: (default is 110) R4# show ip ospf Routing Process "ospf 1" with ID 172.16.4.1 Start time: 00:30:15.504, Time elapsed: 19:15:39.824 Supports only single TOS(TOS0) routes Supports opaque LSA Supports Link-local Signaling (LLS) Supports area transit capability Router is not originating router-LSAs with maximum metric Initial SPF schedule delay 5000 msecs Minimum hold time between two consecutive SPFs 10000 msecs Maximum wait time between two consecutive SPFs 10000 msecs Incremental-SPF disabled Minimum LSA interval 5 secs Minimum LSA arrival 1000 msecs LSA group pacing timer 240 secs Interface flood pacing timer 33 msecs Retransmission pacing timer 66 msecs Number of external LSA 0. Checksum Sum 0x000000 Number of opaque AS LSA 0. Checksum Sum 0x000000 Number of DCbitless external and opaque AS LSA 0 Number of DoNotAge external and opaque AS LSA 0 Number of areas in this router is 3. 3 normal 0 stub 0 nssa Number of areas transit capable is 0 <output omitted>
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.
R4# show run | section ospf router ospf 1 log-adjacency-changes area 34 virtual-link 172.16.34.3 network 172.16.4.0 0.0.0.255 area 40 network 172.16.34.0 0.0.0.255 area 34
After you correct the problem, you should see the virtual link come up.
R4(config)# router ospf 1 R4(config-router)# no area 34 virtual-link 172.16.34.3 R4(config-router)# area 34 virtual-link 172.16.3.1
You should now have full IP connectivity.
Tcl Verification Script
R1# tclsh
foreach address {
172.16.1.1
172.16.2.1
172.16.3.1
172.16.4.1
172.16.12.1
172.16.12.2
172.16.23.2
172.16.23.3
172.16.34.3
172.16.34.4
} {
ping $address }
Final Device Configurations
Router R1
hostname R1 ! interface Loopback0 ip address 172.16.1.1 255.255.255.0 ! interface Serial0/0/0 ip address 172.16.12.1 255.255.255.0 clock rate 64000 bandwidth 64 no shutdown ! router ospf 1 network 172.16.1.0 0.0.0.255 area 0 network 172.16.12.0 0.0.0.255 area 0 end
Router R2
hostname R2 ! interface Loopback0 ip address 172.16.2.1 255.255.255.0 ! interface Serial0/0/0 ip address 172.16.12.2 255.255.255.0 bandwidth 64 no shutdown ! interface Serial0/0/1 ip address 172.16.23.2 255.255.255.0 ip ospf network non-broadcast clock rate 64000 bandwidth 64 no shutdown ! router ospf 1 network 172.16.2.0 0.0.0.255 area 0 network 172.16.12.0 0.0.0.255 area 0 network 172.16.23.0 0.0.0.255 area 0 neighbor 172.16.23.3 end
Router R3
hostname R3 ! interface Loopback0 ip address 172.16.3.1 255.255.255.0 ! interface Serial0/0/1 ip address 172.16.23.3 255.255.255.0 ip ospf network non-broadcast bandwidth 64 no shutdown ! interface Serial0/1/0 ip address 172.16.34.3 255.255.255.0 clock rate 64000 bandwidth 64 no shutdown ! router ospf 1 area 34 virtual-link 172.16.4.1 network 172.16.3.0 0.0.0.255 area 34 network 172.16.23.0 0.0.0.255 area 0 network 172.16.34.0 0.0.0.255 area 34 end
Router R4
hostname R4 ! interface Loopback0 ip address 172.16.4.1 255.255.255.0 ! interface Serial0/0/0 ip address 172.16.34.4 255.255.255.0 bandwidth 64 no shutdown ! router ospf 1 area 34 virtual-link 172.16.3.1 network 172.16.4.0 0.0.0.255 area 40 network 172.16.34.0 0.0.0.255 area 34 end
More Resources