Vidipac VSW7242, User Manual, Page: 91 / 288

4.7 Spanning Tree
The switch supports Multiple Spanning Tree Protocol (MSTP), Rapid Spanning Tree Protocol
(RSTP) and Legacy Spanning Tree Protocol (STP).
The STP and RSTP is combined and defined in IEEE 802.1D-2004, Rapid Spanning Tree
Protocol. The RSTP protocol is applied to single network domain no matter how many VLANs in
your network. In RSTP domain, one of the switch acts as the Root Switch and block one of the
link with highest path cost to avoid network loop. There are maximum 23 level switches within
one RSTP domain, the network size may be limited.
Multiple Spanning Tree Protocol (MSTP) is a direct extension of RSTP. It can provide an
independent spanning tree for different VLANs. With the Spanning Tree and VLAN mapping,
each VLAN has its own root and blocking path, the STP region size becomes lower, the
convergence time of topology change becomes faster as well.
There are some important abbreviation as below.
Common Spanning Tree (CST): Common Spanning Tree (CST) interconnects all adjacent
MST regions and acts as a virtual bridge node for communications with STP or RSTP nodes in
the global network.
Common and Internal Spanning Tree (CIST): MSTP connects all bridges and LAN segments
with a single Common and Internal Spanning Tree (CIST). The CIST is formed as a result of the
running spanning tree algorithm between switches that support the STP, RSTP, MSTP
protocols.
MSTI: Multiple Spanning Tree Instance: One VLAN can be mapped to a MSTI. Each instance
has its own root switch, forwarding path, blocking path and table. An MST Region may contain
multiple MSTI.
4.7.1 Spanning Tree / Bridge Setting
This page allows you to configure STP system settings. The settings are used by all STP Bridge
instances in the Switch.