NETGEAR AV Line M4250 GSM4210PX 8-Port Gigabit PoE+ Compliant Managed AV Switch with SFP (220W) - Manual (Page 779)

Multiple Spanning Tree Protocol
Spanning Tree Protocol (STP) runs on bridged networks to help eliminate loops. If a
bridge loop occurs, the network can become flooded with traffic. IEEE 802.1s Multiple
Spanning Tree Protocol (MSTP) supports multiple instances of spanning tree to efficiently
channel VLAN traffic over different interfaces. Each instance of the spanning tree behaves
in the manner specified in IEEE 802.1w, Rapid Spanning Tree, with slight modifications
in the working but not the end effect (chief among the effects is the rapid transitioning
of the port to the forwarding state).
The difference between the RSTP and the traditional STP (IEEE 802.1D) is the ability to
configure and recognize full-duplex connectivity and ports that are connected to end
stations, resulting in rapid transitioning of the port to the Forwarding state and the
suppression of Topology Change Notification. These features are represented by the
parameters pointtopoint and edgeport. MSTP is compatible to both RSTP and STP. It
behaves in a way that is appropriate for STP and RSTP bridges.
An MSTP bridge can be configured to behave entirely as a RSTP bridge or an STP bridge.
So, an IEEE 802.1s bridge inherently also supports IEEE 802.1w and IEEE 802.1D.
The MSTP algorithm and protocol provide simple and full connectivity for frames
assigned to any VLAN throughout a bridged LAN comprising arbitrarily interconnected
networking devices, each operating MSTP, STP, or RSTP. MSTP allows frames assigned
to different VLANs to follow separate paths, each based on an independent Multiple
Spanning Tree Instance (MSTI), within Multiple Spanning Tree (MST) regions composed
of LANs and or MSTP bridges. These regions and the other bridges and LANs are
connected into a single Common Spanning Tree (CST). (IEEE DRAFT P802.1s/D13)
MSTP connects all bridges and LANs with a single Common and Internal Spanning Tree
(CIST). The CIST supports the automatic determination of each MST region, choosing
its maximum possible extent. The connectivity calculated for the CIST provides the CST
for interconnecting these regions, and an Internal Spanning Tree (IST) within each region.
MSTP ensures that frames with a VLAN ID are assigned to one and only one of the MSTIs
or the IST within the region, that the assignment is consistent among all the networking
devices in the region, and that the stable connectivity of each MSTI and IST at the
boundary of the region matches that of the CST. The stable active topology of the
bridged LAN with respect to frames consistently classified as belonging to any VLAN
thus simply and fully connects all LANs and networking devices throughout the network,
though frames belonging to different VLANs can take different paths within any region,
per IEEE DRAFT P802.1s/D13.
All bridges, whether they use STP, RSTP, or MSTP, send information in configuration
messages through Bridge Protocol Data Units (BPDUs) to assign port roles that determine
each port’s participation in a fully and simply connected active topology based on one
or more spanning trees. The information communicated is known as the spanning tree
priority vector. The BPDU structure for each of these different protocols is different. An
Main User Manual 779 Configuration Examples
AV Line of Fully Managed Switches M4250 Series Main User Manual