IMPORTANT: Be sure to set switches to allow MAC addresses to move from one port to another without waiting for an expiration period or causing a lock out.

Always enable the "spanning tree portfast" feature to allow the switch port to bypass the "listening" and "learning" stages of spanning tree and quickly transition to the "forwarding" stage, allowing edge devices to immediately begin communication on the network.

Network loop protection

To avoid network loops, Virtual Connect first verifies that only one active uplink exists per network from the Virtual Connect domain to the external Ethernet switching environment. Second, Virtual Connect makes sure that no network loops are created by the stacking links between Virtual Connect modules.

•One active link—A VC uplink set can include multiple uplink ports. To prevent a loop with broadcast traffic coming in one uplink and going out another, only one uplink or uplink LAG is active at a time. The uplink or LAG with the greatest bandwidth should be selected as the active uplink. If the active uplink loses the link, then the next best uplink is made active.

•No loops through stacking links—If multiple VC-Enet modules are used, they are interconnected using stacking links, which might appear as an opportunity for loops within the VC environment. For each individual network in the Virtual Connect environment, VC blocks certain stacking links to ensure that each network has a loop-free topology.

Enhanced network loop protection detects loops on downlink ports, which can be a Flex-10 logical port or physical port. The feature applies to Flex-10 logical function if the Flex-10 port is operating under the control of DCC protocol. If DCC is not available, the feature applies to a physical downlink port.

Enhanced network loop protection uses two methods to detect loops:

•It periodically injects a special probe frame into the VC domain and monitors downlink ports for the looped back probe frame. If this special probe frame is detected on downlink ports, the port is considered to cause the loop condition.

For tunneled networks, the probe frame transmission is extended over a longer period of time proportional to the number of tunneled networks. The probe frames are sent on a subset of tunnels every second until all tunnels are serviced.

•It monitors and intercepts common loop detection frames used in other switches. In network environments where the upstream switches send loop detection frames, the VC Enet modules must ensure that any downlink loops do not cause these frames to be sent back to the uplink ports. Even though VC probe frames ensure loops are detected, there is a small time window depending on the probe frame transmission interval in which the loop detection frames from the external switch might loop through down link ports and reach uplink ports. By intercepting the external loop detection frames on downlinks, the possibility of triggering loop protection on the upstream switch is eliminated. When network loop protection is enabled, VC-Enet modules intercept the following types of loop detection frames:

o PVST+ BPDUs

o Procurve Loop Protect frames

When the network loop protection feature is enabled, any probe frame or other supported loop detection frame received on a downlink port is considered to be causing the network loop, and the port is disabled immediately until an administrative action is taken. The administrative action involves resolving the loop condition and clearing the loop protection error condition. The "loop detected" status on a port can be cleared by one of the following administrative actions:

•Restart loop detection by issuing "reset" loop protection from the CLI or GUI

Virtual Connect networks 100