Multiple Stp - ZyXEL Communications MSC1000G User Manual

Chapter 13 Switch Screens
RSTP assigns three port states to eliminate packet looping while STP assigns five (see following
table). A device port is not allowed to go directly from blocking state to forwarding state so as to
eliminate transient loops.
Table 278 RSTP and STP Port States
RSTP PORT STATE STP PORT STATE DESCRIPTION
Discarding
Discarding
Discarding
Learning
Forwarding

13.11.2 Multiple STP

Multiple Spanning Tree Protocol (IEEE 802.1s) is backward compatible with STP/RSTP and
addresses the limitations of existing spanning tree protocols (STP and RSTP) in networks to include
the following features:
• One Common and Internal Spanning Tree (CIST) that represents the entire network's
connectivity.
• Grouping of multiple bridges (or switching devices) into regions that appear as one single bridge
on the network.
• Multiple Spanning Tree Instances (Mists) that allow multiple VLANs to use the same spanning
tree.
• Load-balancing is possible as traffic from different VLANs can use distinct paths in a region.
13.11.2.1 MSTP Network Example
The following figure shows a network example where two VLANs are configured on the two
switches. If the switches are using STP or RSTP, the link for VLAN 2 will be blocked as STP and RSTP
allow only one link in the network and block the redundant link.
524
Disabled STP is disabled (default).
Blocking Only configuration and management BPDUs are received and
processed.
Listening All BPDUs are received and processed.
Learning All BPDUs are received and processed. Information frames are
submitted to the learning process but not forwarded.
Forwarding All BPDUs are received and processed. All information frames are
received and forwarded.
Management Switch Card User's Guide