Specifications

ALAXALA Ring Configuration Guide (Edition 1)

2.4 Operation when the Ring Protocol and STP are used together

A network in which the ring network and STP are used together runs by using a method called the virtual link.

This method allows STP control frames (BPDUs) to be transferred on the ring network and entries in the MAC

address table for the ring ports to be cleared when a topology is changed.

The following figure shows an overview of using the ring network with STP by using the virtual link.

2.4.1 Normal operation

Figure 2.4-1 Overview of using the Ring Protocol and STP through virtual link

BPDU is a control frame sent and received between STP-configured nodes. BPDUs are encapsulated and

transferred on a virtual link VLAN in a ring network. A virtual link ID identifies the target nodes to allow

BPDUs to be sent and received among the nodes. A node with a different virtual ID only forwards the received

frame to the next node. The node with the same virtual link ID decapsulates and receives control frames from the

partner node. This allows you to build a closed STP topology in an independent base with the same virtual link

ID.

When virtual link control frames are transferred through the ring network, two physical lines in both clockwise

and counter-clockwise directions exist. The virtual link control frames are actually transferred in both directions

in the ring network. If no failure is found in the ring network, one frame stops at the BLK port on the master node.

If a failure is found, one frame is discarded at the failure point. The partner node in the same base receives the