Cisco Catalyst 4500 series Administration Manual page 737

Chapter 26 Configuring EtherChannel and Link State Tracking
Figure 26-3 on page 26-20
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.
The configuration in
For links to switches and other network devices
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Link-state group 1 on switch A
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• Link-state group 2 on switch A
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Link-state group 2 on switch B
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Link-state group 1 on switch B
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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
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remain in the link-up state.
If all of the upstream interfaces become unavailable, link-state tracking automatically puts the
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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.
OL_28731-01
shows a network configured with link-state tracking. To enable link-state
Figure 26-3 ensures that the network traffic flow is balanced as follows:
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.
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.
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.
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
Understanding Link-State Tracking
26-19