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Verifying the OSPF Protocol

 

Purpose

After you have verified that the LSP is down, and the cause is not in the physical, datalink, or IP layer, verify the OSPF configuration. Check the routers in your network to ensure that the interfaces and the OSPF protocol are configured correctly, and that the neighbors are established.

Figure 1: MPLS Network Broken at the OSPF Protocol Layer
MPLS Network Broken at the OSPF Protocol
Layer


Verify the LSP

Purpose

Confirm that interfaces are configured for OSPF, the OSPF protocol is configured correctly and that neighbors are established.

Action

To verify the LSP, enter the following command on the ingress, transit, and egress routers:

Sample Output 1

Sample Output 2

Sample Output 3

Sample Output 4

Sample Output 5

Sample Output 6

Meaning

Sample Outputs 1, 2, and 3 show that the LSP and the reverse LSP are down:

  • Sample Output 1 from ingress router R1 shows that LSP R1-to-R6 does not have a route towards the destination (R6).

  • Sample Output 2 from transit router R3 shows that there are no LSP sessions.

  • Sample Output 3 from egress router R6 also shows that reverse LSP R6-to-R1 is down.

Sample Outputs 4, 5, and 6 show that the LSP is up and the reverse LSP is down:

  • Sample Output 4 from ingress router R1 shows that LSP R1-to-R6 is up and there are no egress LSP sessions.

  • Sample Output 5 from transit router R3 shows that there is one ingress LSP session (R1-to-R6) and no egress LSP sessions.

  • Sample Output 6 from egress router R6 shows that LSP R6-to-R1 is down due to an MPLS label allocation failure.



Verify OSPF Interfaces

Purpose

After you have verified that the LSP is down, and the cause is not in the physical, data link, or IP layer, check the routers in your network to determine that all relevant OSPF interfaces are configured correctly.

Action

To verify OSPF interfaces, enter the following commands from the ingress, transit, and egress routers:

Sample Output 1

Sample Output 2

Meaning

Sample Output 1 shows that all interfaces on all routers are in the correct area (0.0.0.0), and the loopback (lo0) interface is missing from the list of interfaces on all routers. The missing loopback (lo0) interface is a problem in this configuration.

In an MPLS network configured with OSPF as the IGP, when you manually configure the RID, it is important to explicitly configure the loopback interface at the [edit protocols ospf] hierarchy level. If the RID is not manually configured, OSPF automatically advertises the loopback (lo0) interface. In the configuration of all the routers in this network, the RID is configured manually, therefore, the loopback (lo0) interface must be explicitly configured at the [edit protocols ospf] hierarchy level. In addition, the loopback (lo0) interface is configured with the passive statement to ensure that the protocols are not run over the loopback (lo0) interface and it is correctly advertised throughout the network.

Sample Output 2 shows that all the relevant interfaces on the ingress, transit, and egress routers, including the loopback (lo0) interface, are in the correct area (0.0.0.0). Because the configuration of the interfaces is correct, further investigation is required to determine the reason for the LSP problem.



Verify OSPF Neighbors

Purpose

After you have checked OSPF interfaces, check your network topology to determine that all relevant neighbors are established.

Action

To verify OSPF neighbors, enter the following commands from the ingress, transit, and egress routers:

Sample Output

Meaning

The sample output shows that all neighbors are fully adjacent, indicating that each router has exchanged a full copy of its link-state database with the other routers, passed through several neighbor states, and become fully adjacent. These adjacencies are created by router link and network link advertisements.



Verify the OSPF Protocol Configuration

Purpose

After you have checked interfaces and neighbors, verify the OSPF protocol configuration.

Action

To verify the OSPF protocol configuration, enter the following command from the ingress, transit, and egress routers:

Sample Output 1

Sample Output 2

Sample Output 3

Meaning

All three sample outputs show that the loopback interface is not included on any of the routers. Including the loopback (lo0) interface is important when you have the RID manually configured.

In addition, Sample Output 2 from transit router R3 shows that traffic engineering is not configured. Traffic engineering must be manually enabled when you configure OSPF for an MPLS network.

Because the loopback interface and traffic engineering are missing from the OSPF protocol configuration, the LSP does not work as expected.



Take Appropriate Action

Problem

Description: Depending on the error you encountered in your investigation, you must take the appropriate action to correct the problem. In this example, the loopback (lo0) interface is missing from all routers, and traffic engineering is missing from the transit router (R3).

Solution

To correct the errors in this example, follow these steps:

  1. Include the loopback (lo0) interface on all routers that have the RID manually configured. Enter the following configuration mode commands:

  2. Move up one level of the configuration hierarchy:

  3. Include traffic engineering on the transit router (R3). Enter the following configuration mode command:

  4. On all routers, verify and commit the configuration:

Sample Output

Meaning

The sample output shows that the loopback (lo0) interface and traffic engineering are now correctly configured on transit router R3. When traffic engineering is configured, OSPF advertises the traffic engineering capabilities of the links.

In the OSPF configuration, you must manually include the loopback (lo0) interface and set it to passive when you manually configure an RID. Setting the loopback (lo0) interface to passive ensures that protocols are not run over the loopback (lo0) interface and the loopback (lo0) interface is advertised correctly throughout the network.. If you do not manually configure an RID, there is no need to explicitly include the loopback interface because the OSPF protocol automatically includes the loopback (lo0) interface.

For more information about configuring LSPs and MPLS, see the Junos MPLS Applications Configuration Guide.



Verify the LSP Again

Purpose

After taking the appropriate action to correct the error, the LSP needs to be checked again to confirm that the problem in the IS-IS protocol has been resolved.

Action

To verify that the LSP is up and traversing the network as expected, enter the following command from the ingress, egress, and transit routers:

Sample Output

Meaning

The sample output from ingress router R1 and egress router R6 shows that the LSP is now traversing the network along the expected path, from R1 through R3 to R6, and the reverse LSP, from R6 through R3 to R1. In addition, the sample output from transit router R3 shows that there are two transit LSP sessions, one from R1 to R6, and the other from R6 to R1.