Consolidated Platform Configuration Guide, Cisco Ios Release 15.2(4)E (Catalyst 2960-X Switches - Cisco Catalyst 2960 series Configuration Manual

Understanding Link-State Tracking
• Link-state group 2 on switch A
• Link-state group 2 on switch B
• Link-state group 1 on switch B
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.
Related Topics
How to Configure Link-State Tracking , on page 369

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◦ 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.
◦ 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.
◦ 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.
◦ 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.