Rstp; Mstp - AMX NXA-ENET8-2POE Operation/Reference Manual

Configuring the NXA-ENET8-2POE
If a bridge does not get a Hello BPDU after a predefined interval (Maximum Age), the bridge assumes that the
link to the Root Bridge is down. This bridge will then initiate negotiations with other bridges to reconfigure the
network to reestablish a valid network topology.

RSTP

RSTP is designed as a general replacement for the slower, legacy STP. RSTP is also incorporated into MSTP.
RSTP achieves must faster reconfiguration (i.e., around 1 to 3 seconds, compared to 30 seconds or more for
STP) by reducing the number of state changes before active ports start learning, predefining an alternate route
that can be used when a node or port fails, and retaining the forwarding database for ports insensitive to
changes in the tree structure when reconfiguration occurs.

MSTP

When using STP or RSTP, it may be difficult to maintain a stable path between all VLAN members. Frequent
changes in the tree structure can easily isolate some of the group members. MSTP (which is based on RSTP
for fast convergence) is designed to support independent spanning trees based on VLAN groups. Using
multiple spanning trees can provide multiple forwarding paths and enable load balancing. One or more
VLANs can be grouped into a Multiple Spanning Tree Instance (MSTI). MSTP builds a separate Multiple
Spanning Tree (MST) for each instance to maintain connectivity among each of the assigned VLAN groups.
MSTP then builds a Internal Spanning Tree (IST) for the Region containing all commonly configured MSTP
bridges (FIG. 67).
FIG. 67 MSTP Region, Internal Spanning Tree, Multiple Spanning Tree
An MST Region consists of a group of interconnected bridges that have the same MST Configuration
Identifiers (including the Region Name, Revision Level and Configuration Digest – see the Configuring
Multiple Spanning Trees section on page 93. An MST Region may contain multiple MSTP Instances. An
Internal Spanning Tree (IST) is used to connect all the MSTP switches within an MST region. A 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 (FIG. 68).
FIG. 68 Common Internal Spanning Tree, Common Spanning Tree, Internal Spanning Tree
MSTP connects all bridges and LAN segments with a single Common and Internal Spanning Tree (CIST).
90 NXA-ENET8-2POE Gigabit Ethernet Layer 2 PoE Switch