Bridge Group Requirements for High Availability

There are special considerations for high availability when using bridge groups.

When the active unit fails over to the standby unit, the switch port running Spanning Tree Protocol (STP) can go into a blocking state for 30 to 50 seconds when it senses the topology change. To avoid traffic loss on the bridge group member interfaces while the port is in a blocking state, you can configure one of the following workarounds:

• Switch port is in Access mode—Enable the STP PortFast feature on the switch:

  
  interface interface_id
    spanning-tree portfast
  
  

  The PortFast feature immediately transitions the port into STP forwarding mode upon linkup. The port still participates in STP. So if the port is to be a part of the loop, the port eventually transitions into STP blocking mode.

• If the switch port is in Trunk mode, or you cannot enable STP PortFast, then you can use one of the following less desirable workarounds that impacts failover functionality or STP stability:

  • Disable interface monitoring on the bridge group and member interfaces.

  • Increase the interface hold time in the failover criteria to a high value that will allow STP to converge before the unit fails over.

  • Decrease the STP timers on the switch to allow STP to converge faster than the interface hold time.