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Examining a CSPF Failure

 

When a local CSPF failure indicates that no path meets the constraints configured for the LSP, you must perform CSPF-based tracing and be familiar with the contents of the traffic engineering database to resolve the problem. See Examine the Traffic Engineering Database for an analysis of the traffic engineering database.

Note

If an LSP does not establish immediately, wait at least a minute or so before taking diagnostic or corrective action. This is because the RSVP retry timer is set to a 30-second default, resulting in a slight delay before the correct state of the LSP is available.

To examine a CSPF failure, follow these steps:



Verify the CSPF Failure

Purpose

To simulate a configuration error on the network, router R5 has the administrative group coloring removed from interface so-0/0/0. The result is a CSPF failure at R5 because there is no longer a path between R1 and R6 that includes the red color.

Action

To confirm that the LSP is down and verify the configuration on routers R1 and R5, enter the following Junos OS CLI operational mode commands:

Sample Output 1

Sample Output 2

Meaning

Sample Output 1 from ingress router R1 shows that the clear mpls lsp command was issued to confirm that R1 cannot reestablish LSP R1-to-R6. The sample output from the show mpls lsp extensive command shows that LSP R1-to-R6 is down, State: Dn and ActivePath: (None); and that the CSPF has failed, CSPF failed: no route toward 10.0.0.6.

Sample Output 2 from transit router R5 shows that LSP R1-to-R6 is not included in the output, indicating that the LSP is not transiting R5.

Most network problems appear as a local CSPF failure, as shown in the sample output. The CSPF failure indicates that no path meeting the constraints for the LSP can be found in the router’s traffic engineering database. To resolve these problems effectively, use CSPF tracing on the ingress router, and analyze the traffic engineering database to locate the node that should meet the constraints.



Examine the CSPF Log File

Purpose

After you have confirmed that the LSP is down, obtain more information about the possible cause of the failure.

Note

To obtain useful information from the CSPF log file, make sure that CSPF tracing is configured on the ingress router.

Action

To examine the CSPF log file, enter the following Junos OS CLI operational mode commands:

Note

To stop monitoring CSPF, issue the monitor stop command.

Sample Output

Meaning

The sample output shows that the monitor start cspf command was issued to start displaying entries in the cspf log file in real time. The cspf log file is generated by the routing protocol process after the file is configured with the traceoptions statement at the [edit protocols mpls] hierarchy level. In this example, the cspf log file is configured with the cspf, cspf-node, and cspf-link flags to provide the most granular information about the steps taken by the CSPF algorithm.

The only link that passes the color constraint is between R1 and R5, 10.1.15.0/32. The CSPF algorithm is a locally run algorithm, which makes its calculations on a given router. When the CSPF algorithm runs on R5, it prunes 10.1.15.2 and selects 10.1.56.1 to send the message to R6.The link between R5 and R6 10.1.56.0/32 does not pass the color constraints, indicating a problem with R5. At this stage, it is useful to examine the traffic engineering database to determine which link on R5 should be associated with the red color.



Examine the Traffic Engineering Database

Purpose

Examining the traffic engineering database is another way to locate the node that should meet the constraints but does not. Once identified, you can concentrate your troubleshooting efforts on why that node is not being represented accurately in the database.

The contents of the traffic engineering database are consistent among all routers within a given traffic engineering domain. Therefore, you can issue the show ted database command from any router in the same traffic engineering domain to obtain more granular information about the CSPF failure.

CSPF integrates topology link-state information that is learned from the IGP traffic engineering extensions and maintained in the traffic engineering database. The information stored in the traffic engineering database includes attributes associated with the state of the network resources (such as total link bandwidth, reserved link bandwidth, available link bandwidth, and link color). When calculating a path, the CSPF algorithm factors in user–provided information such as bandwidth requirements, maximum allowed hop count, and administrative groups, all of which are obtained from user configuration. (See Figure 1).

Figure 1: User–Provided Constraints
User–Provided Constraints

Action

To examine the traffic engineering database, enter the following Junos OS CLI operational mode commands:

Sample Output 1

Sample Output 2

Meaning

Sample Output 1 from ingress router R1 shows a wealth of information on each node in the network, although only a portion is included in this example. The output shows the total number of IS-IS and INET nodes in the traffic engineering domain. The portion of the traffic engineering database shown represents a node (R5), and the Type field indicates Rtr (router). The Type field could also indicate Net (network) if the node were a pseudo node. The node (R5) has three input and output links that are running IS-IS Level 2, Protocol: IS-IS(2). The links lead to nodes R1, R4, and R6. The local address and remote address for each link is specified. The information on each node includes administrative groups (Color:), metrics, static bandwidth, reservable bandwidth, and available bandwidth priority level. The information contained in the traffic engineering database should be the same across all routers in the same traffic engineering domain. For a detailed description of the fields in the output of the show ted database extensive command, see the Junos Routing Protocols and Policies Command Reference.

Sample Output 2 shows filtered output that allows you to focus on exactly what is missing or incorrect.

Both outputs confirm that the link between R1 and R5, 10.1.15.0/32, is associated with the red color, while the link between R5 and R6, 10.1.56.0/32, is not associated with a color. In the network shown in CSPF Topology with Administrative Group Coloring, for the LSP to establish correctly, link 10.1.56.1 must be associated with the red color.



Check the Administrative Group Configuration on R5

Purpose

Focus on R5 to determine which interfaces are associated with the red color, and make any necessary corrections.

Action

To check the administrative group configuration on R5 and make any necessary corrections, enter the following Junos OS CLI commands:

Sample Output 1

Sample Output 2

Sample Output 3

Meaning

Sample Output 1 from transit router R5 shows that at the [edit protocols mpls] hierarchy level, interface so-0/0/1 is incorrectly configured with the admin-group red statement. The so-0/0/0 interface should be configured with the admin-group red statement.

Sample Output 2 shows the steps taken to correct the configuration. The administration group has been deleted from so-0/0/1 and so-0/0/0 is now associated with the red color.

Sample Output 3 shows that LSP R1-to-R6 is established.