ZyXEL ES-2108PWR User Guide - Page 103

Chapter 11 Spanning Tree Protocol 11.1.3 STP Port States STP assigns five port states to eliminate packet looping. A bridge port is not allowed to go directly from blocking state to forwarding state so as to eliminate transient loops. Table 23 STP Port States PORT STATE DESCRIPTION Disabled STP is disabled (default). Blocking Only configuration and management BPDUs are received and processed. Listening All BPDUs are received and processed. Learning Forwarding Note: The listening state does not exist in RSTP. All BPDUs are received and processed. Information frames are submitted to the learning process but not forwarded. All BPDUs are received and processed. All information frames are received and forwarded. 11.1.4 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. • A VLAN can be mapped to a specific Multiple Spanning Tree Instance (MSTI). MSTI allows multiple VLANs to use the same spanning tree. • Load-balancing is possible as traffic from different VLANs can use distinct paths in a region. 11.1.4.1 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. ES-2108 Series User's Guide 103