Design Reference

Figure 13: VLAN isolation
MSTP and RSTP considerations
The Spanning Tree Protocol (STP) provides loop protection and recovery, but it is slow to respond
to a topology change in the network (for example, a dysfunctional link in a network). RSTP (IEEE
802.1w) and MSTP (IEEE 802.1s) reduce the recovery time after a network failure. RSTP and
MSTP also maintain a backward compatibility with IEEE 802.1D. Typically, the recovery time of
RSTP and MSTP is less than 1 second. RSTP and MSTP also reduce the amount of flooding in the
network by enhancing the way that Topology Change Notification (TCN) packets are generated.
Use MSTP to configure MSTIs on the same switch. Each MSTI can include one or more VLANs.
In MSTP mode you can configure up to 64 instances. Instance 0 or Common and Internal Spanning
Tree (CIST) is the default group, which includes default VLAN 1. Instances 1 to 63 are MSTIs.
MSTP and RSTP considerations
January 2015 Network Design Reference for Avaya VSP 4000 Series 53
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