15.1.3 Overview of Uplink and Redundant Operation

Uplink redundancy provides redundancy by using a pair of ports or bundles of ports (aggregated link ports). This pair of ports is called an uplink port pair. An uplink port pair consists of a primary port that performs communication during normal operation and a secondary port that takes over as the primary port in case of a failure. You can configure these ports by using configuration commands.

The primary port and the secondary port do not need to have the same bandwidth or consist of the same number of ports. For example, you can specify a 10 Gigabit Ethernet port as the primary port and a link aggregation group consisting of five 1 Gigabit Ethernet ports as the secondary port.

In the uplink port pair, the port that is currently performing communication is called the active port. The other port is called the standby port, and it stands ready to take over as the active port if the active port fails so that communication can continue.

The ports of the uplink port pair must belong to the same VLAN and have the same settings. In addition, the ports used for an uplink port pair cannot be used as another uplink port pair.

The following figure provides an overview of uplink redundancy operation.

Figure 15-2: Overview of uplink redundant operations

Normal operation

Communication with upstream switches is possible via the primary port on the Switch. The secondary port on the Switch is not communicating.

If the primary port fails

If the primary port link goes down, the Switch switches the active port to the secondary port and uses it to continue communication with upstream switches. This action is called a switchover. At this time, the secondary port, which is now the active port, sends a special control frame called a flush control frame or an MAC address update frame to the upstream switches. When the upstream switches receive either frame, they update their MAC address tables and immediately resume communication.

When the primary port is restored

When the primary port link is enabled and the port is standing by, you can use automatic switch-back or execute the appropriate operation command on the Switch to switch the active port to the primary port. This action is called switch-back.

Similar to switching, communication can be recovered quickly by sending a flush control frame or a MAC address update frame, or by temporarily bringing down the old active port by the port reset function.