Configuring Link-State Tracking

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Restrictions for Configuring Link-State Tracking

  • You can configure only two link-state groups per switch.

  • An interface cannot be a member of more than one link-state group.

  • An interface that is defined as an upstream interface in a link-state group cannot also be defined as a downstream interface in the link-state group.

  • Do not enable link-state tracking on individual interfaces that will part of a downstream EtherChannel interface.

Understanding Link-State Tracking

Link-state tracking, also known as trunk failover, binds the link state of multiple interfaces. Link-state tracking can be with server NIC adapter teaming to provide redundancy in the network. When the server NIC adapters are configured in a primary or secondary relationship, and the link is lost on the primary interface, network connectivity is transparently changed to the secondary interface.

To enable link-state tracking, create a link-state group, and specify the interfaces that are assigned to the link-state group. An interface can be an aggregation of ports (an EtherChannel), a single physical port in access or trunk mode, or a routed port. In a link-state group, these interfaces are bundled together. The downstream interfaces are bound to the upstream interfaces. Interfaces connected to servers are referred to as downstream interfaces, and interfaces connected to distribution switches and network devices are referred to as upstream interfaces.

Note
Note

An interface can be an aggregation of ports (an EtherChannel) or a single physical port in either access or trunk mode .

The configuration in this figure ensures that the network traffic flow is balanced.

Figure 1. Typical Link-State Tracking Configuration


  • For links to switches and other network devices

    • Server 1 and server 2 use switch A for primary links and switch B for secondary links.

    • Server 3 and server 4 use switch B for primary links and switch A for secondary links.

  • Link-state group 1 on switch A

    • Switch A provides primary links to server 1 and server 2 through link-state group 1. Port 1 is connected to server 1, and port 2 is connected to server 2. Port 1 and port 2 are the downstream interfaces in link-state group 1.

    • Port 5 and port 6 are connected to distribution switch 1 through link-state group 1. Port 5 and port 6 are the upstream interfaces in link-state group 1.

  • Link-state group 2 on switch A

    • Switch A provides secondary links to server 3 and server 4 through link-state group 2. Port 3 is connected to server 3, and port 4 is connected to server 4. Port 3 and port 4 are the downstream interfaces in link-state group 2.

    • Port 7 and port 8 are connected to distribution switch 2 through link-state group 2. Port 7 and port 8 are the upstream interfaces in link-state group 2.

  • Link-state group 2 on switch B

    • Switch B provides primary links to server 3 and server 4 through link-state group 2. Port 3 is connected to server 3, and port 4 is connected to server 4. Port 3 and port 4 are the downstream interfaces in link-state group 2.

    • Port 5 and port 6 are connected to distribution switch 2 through link-state group 2. Port 5 and port 6 are the upstream interfaces in link-state group 2.

  • Link-state group 1 on switch B

    • Switch B provides secondary links to server 1 and server 2 through link-state group 1. Port 1 is connected to server 1, and port 2 is connected to server 2. Port 1 and port 2 are the downstream interfaces in link-state group 1.

    • Port 7 and port 8 are connected to distribution switch 1 through link-state group 1. Port 7 and port 8 are the upstream interfaces in link-state group 1.

In a link-state group, the upstream ports can become unavailable or lose connectivity because the distribution switch or router fails, the cables are disconnected, or the link is lost. These are the interactions between the downstream and upstream interfaces when link-state tracking is enabled:

  • If any of the upstream interfaces are in the link-up state, the downstream interfaces can change to or remain in the link-up state.

  • If all of the upstream interfaces become unavailable, link-state tracking automatically puts the downstream interfaces in the error-disabled state. Connectivity to and from the servers is automatically changed from the primary server interface to the secondary server interface. For example, in the previous figure, if the upstream link for port 6 is lost, the link states of downstream ports 1 and 2 do not change. However, if the link for upstream port 5 is also lost, the link state of the downstream ports changes to the link-down state. Connectivity to server 1 and server 2 is then changed from link-state group1 to link-state group 2. The downstream ports 3 and 4 do not change state because they are in link-group 2.

  • If the link-state group is configured, link-state tracking is disabled, and the upstream interfaces lose connectivity, the link states of the downstream interfaces remain unchanged. The server does not recognize that upstream connectivity has been lost and does not failover to the secondary interface.

You can recover a downstream interface link-down condition by removing the failed downstream port from the link-state group. To recover multiple downstream interfaces, disable the link-state group.

How to Configure Link-State Tracking

To enable link-state tracking, create a link-state group and specify the interfaces that are assigned to the group. This task is optional.

SUMMARY STEPS

  1. configure terminal
  2. link state track number
  3. interface interface-id
  4. link state group [number] {upstream | downstream }
  5. end

DETAILED STEPS

  Command or Action Purpose
Step 1

configure terminal

Example:


Switch# configure terminal

Enters global configuration mode.

Step 2

link state track number

Example:


Switch(config)# link state track 2

Creates a link-state group and enables link-state tracking. The group number can be 1 or 2; the default is 1.

Step 3

interface interface-id

Example:


Switch(config)# interface gigabitethernet2/0/1

Specifies a physical interface or range of interfaces to configure, and enters interface configuration mode.

Valid interfaces include switch ports in access or trunk mode (IEEE 802.1q) or routed ports.

Note 

Do not enable link-state tracking on individual interfaces that will be part of an Etherchannel interface.

Step 4

link state group [number] {upstream | downstream }

Example:


Switch(config-if)# link state group 2 upstream

Specifies a link-state group and configures the interface as either an upstream or downstream interface in the group.

Step 5

end

Example:


Switch(config-if)# end

Returns to privileged EXEC mode.

Note 

If the interfaces are part of an EtherChannel, you must specify the port channel name as part of the link-state group, not the individual port members.

Monitoring Link-State Tracking

You can display link-state tracking status using the command in this table.

Table 1. Commands for Monitoring Link-State Tracking Status

Command

Description

show link state group [number] [detail]

Displays the link-state group information.

Configuring Link-State Tracking: Example

This example shows how to create the link-state group 1 and configure the interfaces in the link-state group.


		Switch# configure terminal
		Switch(config)# link state track 1
		Switch(config-if)# interface range gigabitethernet1/0/21-22 
		Switch(config-if)# link state group 1 upstream
		Switch(config-if)# interface gigabitethernet1/0/1
		Switch(config-if)# link state group 1 downstream
		Switch(config-if)# interface gigabitethernet1/0/3
		Switch(config-if)# link state group 1 downstream
		Switch(config-if)# interface gigabitethernet1/0/5
  Switch(config-if)# link state group 1 downstream 
  Switch(config-if)# end

Additional References for Link-State Tracking

Related Documents

Related Topic Document Title

Layer 2 command reference

Command Reference, Cisco IOS Release 15.2(2)E (Catalyst 3750-X and 3560-X Switches)

Standards and RFCs

Standard/RFC Title

None

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