Cisco Nexus 7000 Series NX-OS MPLS Configuration Guide

Path Protection

A secondary label switched path (LSP) is configured and established to provide failure protection for the LSP that is carrying a tunnel’s TE traffic. When there is a failure on the protected LSP, the headend router immediately enables the secondary LSP to temporarily carry the tunnel’s traffic. If there is a failure on the secondary LSP, the tunnel no longer has path protection until the failure along the secondary path is cleared.

Path protection can be used with

• Single area

– Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF)

• Interarea

– Intermediate System-to-Intermediate System (IS-IS) or Open Shortest Path First (OSPF)

• Inter-AS

– Border Gateway Protocol (BGP), both external BGP (eBGP,) and static

The failure detection functions that trigger a switchover to a secondary tunnel include the following:

• Path error or resv tear from RSVP signaling
• Notification from the Bidirectional Forwarding Detection (BFD) protocol that a neighbor is lost
• Notification from the Interior Gateway Protocol (IGP) that the adjacency is down
• Local teardown of the protected tunnel’s LSP due to preemption in order to signal higher priority LSPs, online insertion and removal (OIR), and so forth

An alternate recovery function is Fast Reroute (FRR), which protects MPLS TE LSPs only from link and node failures by locally repairing the LSPs at the point of failure.

Although not as fast as link or node protection, presignaling a secondary LSP is faster than configuring a secondary primary path option or allowing the tunnel’s headend router to dynamically recalculate a path. The actual recovery time is topology-dependent and is affected by delay factors such as propagation delay or switch fabric latency.

Enhanced Path Protection

Enhanced path protection provides support of multiple backup path options per primary path option. You can configure up to eight backup path options for a given primary path option. Only one of the configured backup path options is actively signaled at any time.

After you enter the mpls traffic-eng path-option list command, you can enter the backup path priority in the number argument of the path-option command. A lower identifier represents a higher priority. Priorities are configurable for each backup path option. Multiple backup path options and a single backup path option cannot coexist to protect a primary path option.

ISSU

Cisco In Service Software Upgrade (ISSU) allows you to perform a Cisco NX-OS software upgrade or downgrade while the system continues to forward packets. ISSU takes advantage of the Cisco NX-OS high availability infrastructure (Cisco nonstop forwarding [NSF] with stateful switchover [SSO] and hardware redundancy) and eliminates the downtime that is associated with software upgrades or version changes by allowing changes while the system remains in service. Cisco ISSU lowers the impact that planned maintenance activities have on network service availability; there is less downtime and better access to critical systems.

When path protection is enabled and an ISSU upgrade is performed, path protection performance is similar to that of other TE features.

NSF/SSO

Cisco NSF with SSO provides continuous packet forwarding, even during a network processor hardware or software failure.

Path protection can recover after SSO. A tunnel configured for path protection may have two LSPs signaled simultaneously: the primary LSP that is carrying the traffic and the secondary LSP that carries traffic if there is a failure along the primary path. Only information associated with one of those LSPs, the one that is currently carrying traffic, is synchronized to the standby system. On recovery, the standby system can determine from the checkpointed information whether the LSP was the primary or secondary.

If the primary LSP was active during the switchover, only the primary LSP is recovered. The secondary LSP that was signaled and provided path protection is resignaled after the TE recovery period is complete. This process does not impact the traffic on the tunnel because the secondary LSP was not carrying traffic.

Configuring Explicit Paths for Secondary Paths

You can specify a secondary path that does not include common links or nodes associated with the primary path in case those links or nodes go down.

Prerequisites

You must enable the MPLS TE feature (see the “Configuring MPLS TE”).

Ensure that you are in the correct VDC (or use the switchto vdc command).

SUMMARY STEPS

1. configure terminal

2. mpls traffic-eng configuration

3. [ no ] explicit-path { name path-name | identifier number }

4. index index command ip-address

DETAILED STEPS

Assigning a Secondary Path Option to Protect a Primary Path Option

You can assign a secondary path option in case there is a link or node failure along a path and all interfaces in your network are not protected.

Prerequisites

You must have the MPLS TE feature enabled (see the “Configuring MPLS TE”).

Ensure that you are in the correct VDC (or use the switchto vdc command).

SUMMARY STEPS

1. configure terminal

2. interface tunnel-te number

3. path-option protect number explicit { identifier path-number | name path-name } [ attributes lsp-attributes | bandwidth kbps | lockdown ] [ verbatim ]

DETAILED STEPS

Enhanced Path Protection Configuration Tasks

This section includes the following topics:

• Creating a Path Option List
• Assigning a Path Option List to Protect a Primary Path Option

These tasks are described in the following sections and are shown in Figure 17-2.

Figure 17-2 Network Topology - Enhanced Path Protection

Creating a Path Option List

In enhanced path protection you can create and assign a path option list.

Note To use a secondary path instead, follow the steps in the “Configuring Explicit Paths for Secondary Paths” section.

SUMMARY STEPS

1. configure terminal

2. interface tunnel-te number

3. mpls traffic-eng path-option list [ name pathlist-name | identifier pathlist-number ]

4. path-option number explicit [ name pathoption-name | identifier pathoption-number ]

5. list

6. no [ pathoption-name | pathoption-number ]

7. end

DETAILED STEPS

Assigning a Path Option List to Protect a Primary Path Option

You can assign a path option list in case there is a link or node failure along a path and all interfaces in your network are not protected. See Figure 17-2.

SUMMARY STEPS

1. configure terminal

2. interface tunnel-te number

3. path-option protect number [ attributes lsp-attributes | bandwidth { kbps | subpool kbps } | explicit { identifier path-number | name path-name } | list { name pathlist-name | identifier pathlist-identifier }]

4. end

DETAILED STEPS

Examples

The following example shows how to display the configuration of the primary path and protection path options.

Note To show the status of both LSPs (primary path and protected path), use the show mpls traffic-eng tunnels command with the protection keyword.

The following example shows how to display tunnel path information.

The command output shows no common links or nodes.

Note The Common Link(s) field shows the number of links shared by both primary and secondary paths, from the headend router to the tailend router.

The Common Node(s) field shows the number of nodes shared by both primary and secondary paths, excluding the headend and tailend routers.

The following example shows how to display the status of both LSPs (primary path and protected path) when the protection keyword is specified.

Note Deleting a primary path option has the same effect as shutting down a link. Traffic moves to the protected path.

The command output shows that both primary LSP and secondary LSP are up and protection is enabled:

The following example shows that the primary LSP is down and that the secondary LSP is up and is carrying traffic:

Verifying the Enhanced Path Protection Configuration

To verify the enhanced path protection configuration, refer to Figure 17-4 Figure 17-4and perform the following steps.

Figure 17-4 Network Topology Verification for Enhanced Path Protection

SUMMARY STEPS

1. show running interface tunnel-te number

2. show mpls traffic-eng tunnels tunnel-te number

3. show mpls traffic-eng tunnels tunnel-te number [ brief ] [ protection]

4. show ip rsvp high-availability database { hello | link-management { interfaces [fixed | variable] | system } | lsp [ filter destination ip-address | filter lsp-id lsp-id | filter source ip-address | filter tunnel-id tunnel-id ] | lsp-head [ filter number ] | summary }

DETAILED STEPS

Step 1 show running interface tunnel-te number

This command shows the configuration of the path option and backup path option.

Note To show the status of both LSPs (that is, both the primary path and the protected path), use the show mpls traffic-eng tunnels command with the protection keyword.

switch# show running interface tunnel-te2

Step 2 show mpls traffic-eng tunnels tunnel-te number

This command shows tunnel path information.

The Common Link(s) field shows the number of links shared by both the primary and secondary paths, from the headend router to the tailend router.

The Common Node(s) field shows the number of nodes shared by both the primary and secondary paths, excluding the headend and tailend routers.

As shown in the following output, there are no common links or nodes:

Step 3 show mpls traffic-eng tunnels tunnel-te number [ brief ] [ protection]

Use this command, with the protection keyword specified, to show the status of both LSPs (that is, both the primary path and the protected path).

The following command output shows that the primary LSP is up, and the secondary LSP is up and providing protection:

The following command output shows that the primary LSP is down, and the secondary LSP is up and is actively carrying traffic:

Step 4 show ip rsvp high-availability database { hello | link-management { interfaces [fixed | variable}] | system } | lsp [ filter destination ip-address | filter lsp-id lsp-id | filter source ip-address | filter tunnel-id tunnel-id ] | lsp-head [ filter number ] | summary }

The show ip rsvp high-availability database command displays the contents of the RSVP HA read and write databases used in TE. If you specify the lsp-head keyword, the command output includes path protection information.

Example: Configuring Explicit Paths for Secondary Paths

Figure 17-5 shows a primary path and a secondary path. If there is a failure, the secondary path is used.

Figure 17-5 Primary Path and Secondary Path

The following example shows that the explicit path is named path3441. There is an index command for each router. If there is failure, the secondary path is used.

Example: Assigning a Secondary Path Option to Protect a Primary Path Option

The following example shows that a TE tunnel is configured:

The following example shows that path protection has been configured. Tunnel 500 has path option 10 using path344 and protected by path 3441, and path option 20 using path345 and protected by path348.

Example: Configuring Tunnels Before and After Path Protection

The following example shows information about the primary (protected) path. The following sample output shows that path protection has been configured:

The following example shows information about the secondary path. Tunnel500 is protected. The protection path is used, and the primary path is down. The command output shows the IP explicit paths of the primary LSP and the secondary LSP.

The following example shows how to shut down the interface to use path protection:

The following example shows that the protection path is used and the primary path is down:

The following example shows that protection is enabled:

The following example shows that the interface is up again and the primary path is activated:

The following example shows that path protection has been reestablished and the primary path is being used:

The following example shows that Tunnel-te500 is protected and after a failure, the primary LSP is protected:

Examples of Enhanced Path Protection

This section includes the following topics:

• Example: Creating a Path Option List
• Example: Assigning a Path Option List to Protect a Primary Path Option
• Example: Configuring Tunnels Before and After Path Protection

Example: Creating a Path Option List

Figure 17-6 shows the network topology for enhanced path protection.

Figure 17-6 Network Topology for Enhanced Path Protection

The following example shows how to configures two explicit paths named secondary1 and secondary2.

The following example shows that a path option list of backup paths is created. You define the path option list by using the explicit paths.

Example: Assigning a Path Option List to Protect a Primary Path Option

The following example shows that a traffic engineering tunnel is configured:

The following example shows that path protection has been configured. Tunnel 2 has path option 10 using path primary1 and protected by secondary-list.

Example: Configuring Tunnels Before and After Path Protection

The following example shows information about the primary (protected) path. The following sample output shows that path protection has been configured:

The following shows information about the secondary path. Tunnel 2 is protected.

The following example shows how to shut down the interface to use path protection:

The following example shows that the protection path is used, and the primary path is down:

The following example shows that protection is enabled.

The following example shows that the interface is up again and the primary path is activated.

The following example shows that path protection has been reestablished and the primary path is being used:

The following example shows the contents of the RSVP high availability read and write databases used in TE.

Related Documents

MIBs