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Catalyst 2960 and 2960-S Switches Software Configuration Guide, Release 15.0(1)SE
OL-26520-01
Chapter 38 Configuring EtherChannels and Link-State Tracking
Understanding Link-State Tracking
• Link-state group 1 on switch A
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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.
As an example of a connectivity change from link-state group 1 to link-state group 2 on switch A,
see Figure 38-6 on page 38-23. 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.
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