Avaya P580 User Manual
Page 46
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Avaya P550R, P580, P880, and P882 Multiservice Switch User Guide, v5.3.1
Chapter 1
Figure 1-4. Spanning Tree Models
IEEE802.1D Spanning Tree Protocol Option
All Avaya Multiservice switches participate in a Single Spanning
Tree domain in the IEEE802.1D STP mode. All ports with STP
configured belong to the same spanning tree domain and rules are
as defined in IEEE802.1D. BPDUs are as defined by 802.1D and are
sent out Clear on each link regardless of whether or not the link has
a tagging method defined. As documented in the IEEE specification,
802.1 D Spanning Tree is intended for environments where only
one VLAN is used in the network. If you are using 802.1 D Spanning
Tree in the network and have multiple VLANs, you should set the
P550R, P580, P880, or P882 switches to run Dual-Layer Spanning
Tree.
PER VLAN Spanning Tree Protocol Option
Per-VLAN mode is the Default Spanning Tree setting on all
multiservice switches. In this mode, the switch runs a separate
spanning process for each VLAN. Each logical Spanning Tree has its
own BPDU's which are tagged with the appropriate VLAN
Identifier(s). Under this mode, the switch can participate in as many
Spanning Tree Domains as there are VLANs defined on the switch.
This conforms to a “virtual” bridging model where the switch runs
as if each VLAN is a separate logical bridge (separate Address
Forwarding Tables, separate spanning trees, etc.). If spanning tree is
not required on all VLANs, you can disable it for individual VLANs
on a VLAN by VLAN basis. Also, different root bridges can be
configured with different bridge priorities based upon VLAN. This
will allow load sharing to occur based upon VLAN. Similarly link
costs and priorities can be adjusted on a per-VLAN basis allowing
further load sharing per VLAN.
Single 802.1D Spanning Tree
One Spanning Tree
Longer convergence
One path to and from root for all VLANs
Improper configuration
can shut down Trunk Links
Multi-Level Spanning Tree
Backbone terminates 802.1D STP
Smaller STP Domains
Quicker Convergence
VLAN Load Balancing
Interoperates w/ existing Bridge/Routers