Cisco IE 4000, Software Configuration Manual

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Configuring Link State Tracking
Link State Tracking

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.
As an example of a connectivity change from link state group 1 to link state group 2 on switch A, see Figure 85 on
page 671 . 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.