ZyXEL ES-3124PWR User Guide - Page 104
Multiple STP
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Chapter 11 Spanning Tree Protocol 11.1.5 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. 11.1.5.1 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. Figure 51 STP/RSTP Network Example A VLAN 1 VLAN 2 B With MSTP, VLANs 1 and 2 are mapped to different spanning trees in the network. Thus traffic from the two VLANs travel on different paths. The following figure shows the network example using MSTP. 104 ES-3124 Series User's Guide