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

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Chapter 11 Spanning Tree Protocol
ES-3124 Series User’s Guide
104
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
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.
A
B
VLAN 1
VLAN 2