Netgear XCM8806 Chassis Hardware Installation Guide - Page 738

NETGEAR 8800 Chassis Switch CLI Manual MSTP MSTP logically divides a Layer 2 network into regions. Each region has a unique identifier and contains multiple spanning tree instances (MSTIs). An MSTI is a spanning tree domain that operates within and is bounded by a region. MSTIs control the topology inside the regions. The Common and Internal Spanning Tree (CIST) is a single spanning tree domain that interconnects MSTP regions. The CIST is responsible for creating a loop-free topology by exchanging and propagating BPDUs across regions to form a Common Spanning Tree (CST). MSTP uses RSTP as its converging algorithm and is interoperable with the legacy STP protocols: STP (802.1D) and RSTP (802.1w). Spanning Tree Domains The switch can be partitioned into multiple virtual bridges. Each virtual bridge can run an independent spanning tree instance. Each spanning tree instance is called a Spanning Tree Domain (STPD). Each STPD has its own root bridge and active path. After an STPD is created, one or more VLANs can be assigned to it. A port can belong to multiple STPDs. In addition, a VLAN can span multiple STPDs. The key points to remember when configuring VLANs and STP are: • Each VLAN forms an independent broadcast domain. • STP blocks paths to create a loop-free environment. • Within any given STPD, all VLANs belonging to it use the same spanning tree. Member VLANs When you add a VLAN to an STPD, that VLAN becomes a member of the STPD. The two types of member VLANs in an STPD are: • Carrier • Protected Carrier VLAN A carrier VLAN defines the scope of the STPD, which includes the physical and logical ports that belong to the STPD and if configured, the 802.1Q tag used to transport Multiple Instance Spanning Tree Protocol (EMISTP) or Per VLAN Spanning Tree (PVST+) encapsulated Bridge Protocol Data Units (BPDUs). Only one carrier VLAN can exist in a given STPD, although some of its ports can be outside the control of any STPD at the same time. 738 | Chapter 17. STP Commands