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The port tracking feature is unique to the Cisco MDS 9000 Family of switches. This feature uses information about the operational state of the link to initiate a failure in the link that connects the edge device. This process of converting the indirect failure to a direct failure triggers a faster recovery process towards redundant links. When enabled, the port tracking feature brings down the configured links based on the failed link and forces the traffic to be redirected to another redundant link.
Generally, hosts can instantly recover from a link failure on a link that is immediately (direct link) connected to a switch. However, recovering from an indirect link failure between switches in a WAN or MAN fabric with a keep-alive mechanism is dependent on several factors such as the time out values (TOVs) and on registered state change notification (RSCN) information.
In Figure 9-1, when the direct link 1 to the host fails, recovery can be immediate. However, when the ISL 2 fails between the two switches, recovery depends on TOVs, RSCNs, and other factors.
Figure 9-1 Traffic Recovery Using Port Tracking
The port tracking feature monitors and detects failures that cause topology changes and brings down the links connecting the attached devices. When you enable this feature and explicitly configure the linked and tracked ports, the Cisco NX-OS software monitors the tracked ports and alters the operational state of the linked ports on detecting a link state change.
The following terms are used in this chapter:
Before configuring port tracking, consider the following guidelines:
Table 9-1 lists the default settings for port tracking parameters.
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Port tracking has the following features:
This section includes the following topics:
The port tracking feature is disabled by default in all switches in the Cisco 9000 Family. When you enable this feature, port tracking is globally enabled for the entire switch.
To configure port tracking, enable the port tracking feature and configure the linked port(s) for the tracked port.
To enable port tracking, follow these steps:
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Removes the currently applied port tracking configuration and disables port tracking. |
When you configure the first tracked port, operational binding is automatically in effect. When you use this method, you have the option to monitor multiple ports or monitor ports in one VSAN.
To operationally bind a tracked port, follow these steps:
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Configures the specified interface and enters the interface configuration submode. You can now configure tracked ports. Note This link symbolizes the direct link (1) in Figure 9-1. |
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Tracks interface fc8/6 with interface port-channel 1. When port-channel 1 goes down, interface fc8/6 is also brought down. Note This link symbolizes the ISL (2) in Figure 9-1. |
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Removes the port tracking configuration that is currently applied to interface fc8/6. |
You can control the operational state of the linked port based on the operational states of multiple tracked ports. When more than one tracked port is associated with a linked port, the operational state of the linked port will be set to down only if all the associated tracked ports are down. Even if one tracked port is up, the linked port will stay up.
In Figure 9-2, only if both ISLs 2 and 3 fail, will the direct link 1 be brought down. Direct link 1 will not be brought down if either 2 or 3 are still functioning as desired.
Figure 9-2 Traffic Recovery Using Port Tracking
To track multiple ports, follow these steps:
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Configures the specified interface and enters the interface configuration submode. You can now configure tracked ports. Note This link symbolizes the direct link (1) in Figure 9-2. |
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Tracks interface fc8/6 with interface port-channel 1. When port-channel 1 goes down, interface fc8/6 is also brought down. Note This link symbolizes the ISL (2) in Figure 9-2. |
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Tracks interface fc8/6 with interface fcip 5. When FCIP 5 goes down, interface fc8/6 is also brought down. Note This link symbolizes the ISL (3) in Figure 9-2. |
You can optionally configure one VSAN from the set of all operational VSANs on the tracked port with the linked port by specifying the required VSAN. This level of flexibility provides higher granularity in tracked ports. In some cases, when a tracked port is a TE port, the set of operational VSANs on the port can change dynamically without bringing down the operational state of the port. In such cases, the port VSAN of the linked port can be monitored on the set of operational VSANs on the tracked port.
If you configure this feature, the linked port is up only when the VSAN is up on the tracked port.
Tip The specified VSAN does not have to be the same as the port VSAN of the linked port.
To monitor a tracked port in a specific VSAN, follow these steps:
If a tracked port flaps frequently, then tracking ports using the operational binding feature may cause frequent topology change. In this case, you may choose to keep the port in the down state until you are able to resolve the reason for these frequent flaps. Keeping the flapping port in the down state forces the traffic to flow through the redundant path until the primary tracked port problems are resolved. When the problems are resolved and the tracked port is back up, you can explicitly enable the interface.
Tip If you configure this feature, the linked port continues to remain in the shutdown state even after the tracked port comes back up. You must explicitly remove the forced shut state (by administratively bringing up this interface) of the linked port once the tracked port is up and stable.
To forcefully shut down a tracked port, follow these steps:
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Configures the specified interface and enters the interface configuration submode. You can now configure tracked ports. |
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Removes the port shutdown configuration for the tracked port. |
The show commands display the current port tracking settings for the Cisco MDS switch (see Examples 9-1 to 9-4 ).
Example 9-1 Displays the Linked and Tracked Port Configuration
Example 9-2 Displays a Tracked Port Configuration for a Fibre Channel Interface
Example 9-3 Displays a Tracked Port Configuration for a PortChannel Interface
Example 9-4 Displays a Forced Shutdown Configuration