28.3.2 Access port PVST +

(1) Description

A network can be built using switches that use Single Spanning Tree and switches that support Single Spanning Tree functionality for one tree (abbreviated hereafter simply as Single Spanning Tree) and PVST+. Switches running on Single Spanning Tree are used as edge switches, and Switches are used for core switches. This kind of network configuration has the following advantages:

• Problems that occur on an edge switch for not result in topology changes for other edge switches.

• Load balancing can be performed among core switches.

Single Spanning Tree is connected by access ports. The following figure shows the configuration example. In this example, Single Spanning Tree runs on the edge switches, and PVST+ runs on the core switches. The core switches treat ports connected to edge switches as access ports. A single VLAN is set up for each edge switch.

Figure 28-6: Connections with Single Spanning Tree

(2) When Single Spanning Tree is mixed on an access port

When PVST+ and Single Spanning Tree coexist, Single Spanning Tree stops (switched to Disable status) on the access port.

(3) Configuration mismatch detection function

For ports connected on the same VLAN, if an access port, protocol port, or MAC port is set for the Switch (using an untagged frame), and a trunk port is set for the partner switch (using a tagged frame), communication for this port will not be possible for the corresponding VLAN. Ports like these are detected as configuration mismatches. This mismatch is detected if the Switch has an access port, and the trunk port is set on the partner switch (using a tagged frame). In this case, the corresponding port stops (Disable status). If the trunk port setting (using a tagged frame) is deleted on the partner switch, the stopped status is automatically removed after hello-time x 3 seconds (six seconds by default).