Wan Optimization high availability or redundancy can be achieved by running a backup network cable parallel to the Wanos device.
When running RSTP the Wanos device is placed between two switches, connected via wan0 to the outside switch and lan0 to the inside switch. The backup link is cabled between the same two switches. Hence two cables run between the outside and inside switch. STP will elect a primary and secondary path based on the port id. Place the Wanos ports on the lower port number or configure the switch to make this link the primary path. RSTP should place the backup link in an alternative path status and will switch over to the backup link within a few milliseconds of detecting a loss.
When running Per-Vlan RSTP high availability can be achieved using a single switch. In this case two VLAN’s are created. The Outside VLAN connects the WAN segment and the Inside VLAN connects the LAN segment. In the diagram below, the Router, Wanos wan0 and the backup link is connected to VLAN 10. On the LAN side the Wanos lan0, Data LAN segment and the backup link is connected to VLAN 20. Under normal conditions the Wanos device bridge traffic between the two segments and the backup link is passively idling. When the switch detects a failure on the primary path, the backup link is enabled and immediately placed in the forwarding state. Advance features like loop guard and hello timers can be adjusted to improve convergence times. Example Cisco Switch Config:
spanning-tree mode rapid-pvst interface range fa0/1 -3 description WAN switchport access vlan 10 spanning-tree mode access interface range fa0/4 - 6 description LAN switchport access vlan 20 spanning-tree mode access interface fa0/4 description Primary-Wanos spanning-tree cost 1