Avaya Cajun P882 User Manual page 144

Chapter 4
Need for
Spanning tree
Protocol
Supported
Spanning Tree
Configurations
Problems with
Single Spanning
Tree Instance
IEEE 802.1D
4-14
For a bridging network to function properly, only one active path
can exist between two stations. Multiple active paths between
stations cause loops in the network. If a loop exists in the bridged
network topology, the potential exists for message duplication, and
in some cases a "Broadcast Storm".
Spanning Tree Protocol defines a single spanning tree that spans all
switches in a bridged network. It forces certain redundant data paths
into a standby (blocked) state. If one network segment in the
Spanning Tree Protocol becomes unreachable, or if Spanning Tree
Protocol costs change, the spanning-tree algorithm reconfigures the
spanning-tree topology and reestablishes the bridge port by
activating the standby path.
The Avaya Multiservice Switch supports four different Spanning
Tree configurations.
IEEE 802.1D
Dual-Layer
Per-VLAN (Default setting)
Disabled
IEEE 802.1D - If you use the 802.1D spanning tree option all
VLANs participate in the same spanning tree. The implication is that
after resolving the spanning tree topology, a port will be forwarding,
or blocked for all VLANs.
Dual-Layer - This option is to be used on a switch that is in
between a 802.1D spanning tree domain switch and a per-VLAN
domain switch. This option, allows the switch to terminate a legacy
spanning tree (802.1D) from old bridges that are VLAN incapable,
and interoperate with other per-VLAN spanning tree bridges.
Per-VLAN - If you use the Spanning Tree per VLAN option, each
VLAN runs a separate spanning tree with its own BPDUs. This
allows different ports to blocked or forwarding for different VLANs.
Disabled - Disables Spanning Tree for the entire switch.
Loss of Connectivity - There is a the potential for the loss of
connectivity of a VLAN when using standard Spanning Tree (IEEE
802.1D). Specifically when their is a loop in one VLAN, but not
another, that share the same physical ports. In Figure 4-8, there is a
loop in the physical connections between the two switches. This
loop is in VLAN A, but not in VLAN B. When running single
Avaya P550R, P580, P880, and P882 Multiservice Switch User Guide, Version 5.3.1