Using the Link-State Application in Your Network

You may have devices in your network that have failover capabilities that enhance network redundancy, but they require an action by the switch to which they are connected to trigger that functionality. The Link-State application provides a facility that triggers link loss on downstream links if the associated upstream links go down.

For example, the Link-State application facilitates use of the NIC adapter teaming capability of network servers. NIC adapter teaming constructs primary and secondary relationships with directly connected switches. The switches provide upstream links that connect to other devices that provide the required network access needed by the servers. If the upstream links for the primary relationship lose connectivity, the Link-State feature forces the shutdown of the downstream stream links, triggering the NIC's teaming functionality. The NIC use its secondary relationship to avoid losing data.

The Link-State application uses port-group tracked objects to monitor the state of the upstream links. The Link-State application associates with downstream links, while the upstream links are associated with tracked objects (part of the Tracked Object Manager functionality). If the Tracked Object Manager detects a state change with the upstream links, the Link-State application is informed. If the upstream links are down, the Link-State application brings down the link to the downstream ports, causing link loss. The downstream device reacts to this and initiates its failover capability. Similarly, if the upstream links are up, the Link-State application attempts to bring up the downstream links. There may be other protocols or applications in the system that prevent the link from coming up.

When the Link-State application needs to influence the operational state of the downstream ports, it sets their operational status to down. In order for this feature to function, you must enable the force link down feature with the set forcelinkdown enable command. You can display the cause for port operation status down with the show port operstatuscause command.