Link Failover; Spanning Tree - Avaya P550R User Manual

Chapter 1

Link Failover

Spanning Tree

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Avaya P550R/P580/P880/P882 Multiservice Switch ATM Uplink Module User Guide, Version 2.0
* Note: Link Failover applies to RFC1483 and UNI links only.
In networks that do not support PNNI, you can use link failover as
an alternative to multiple active interfaces. With this feature, one
link is active with all other links designated as standby. If one link
loses its connectivity, a standby link becomes active and the
connections are re-established. Links are weighted to determine
which link attempts to take over first.
The Spanning Tree protocol is used to prevent loops from forming in
your network. The spanning tree algorithm creates a single path
through the network by ensuring that if more than one path exists
between two parts of a network, only one of these paths is used,
while the others are blocked. Because of the number of "bridges"
present in a switched networking environment, spanning tree
structures can become extremely complex. The ATM Uplink module
supports the spanning tree per VLAN option (each LEC has an
independent STP state).
The Web Agent may display what appears to be misleading
Spanning Tree Protocol information. When you are using UNI on
both (physical) ports on the ATM Uplink module, traffic may flow
through either (physical) port 1 or (physical) port 2, depending on
path cost. The Spanning Tree information on the Web Agent will
indicate that Port 1 of the ATM Uplink module is active and
forwarding traffic. This is because from the switch's perspective, it
"sees" the LEC as a Virtual Switch Port, not the actual physical ports.
So regardless of which physical port is passing the traffic, the LEC
(Virtual Switch Port) is seen as active.
* Note: Each VLAN runs a separate spanning tree with its own
Bridge Protocol Data Units (BPDUs). This allows each
LEC to have a spanning tree state that is independent of
the other LECs on its module and does not support
spanning tree on RFC1483 connections.
For more information on spanning tree support and configuration,
refer to the Avaya P550R/P580/P880/P882 Switch User Guide.