Avaya P580 - Manual (Page 48)

1-20 Avaya P550R, P580, P880, and P882 Multiservice Switch User Guide, v5.3.1
Chapter 1
In the previous example, all three multiservice switches participate
in two Spanning Tree domains:
■
Domain for VLAN A containing three bridges
■
Domain for VLAN B containing three bridges with the legacy
domain remaining separate.
The legacy devices need not be aware of the other spanning tree
domains. If a loop forms between the Multilayer domains and the
legacy domain, the proprietary BPDU is seen returning to the
Multilayer domain through the legacy domain and the loop is
blocked. The Dual-Layer Spanning Tree method is preferred when
inter-operating with large legacy bridge networks. Convergence
time is reduced, and management is simplified, by allowing the
legacy bridges to remain in their own spanning tree domain
Global Disable
You can globally disable Spanning Tree on all multiservice switches,
thus preventing any switch port from participating in Spanning
Tree. This is only recommended in a very controlled environment
where there is no possibility of a loop being placed in the network.
Port Settings
You can use the “Bridge Ports” option to adjust link costs and
priorities per IEEE802.1D. You can also disable Spanning Tree
on a per port basis by a per-port port parameter setting. If you
disable Spanning Tree per port, IEEE802.1D definitions are strictly
followed. This means that BPDUs are not sent, incoming BPDUs are
not processed. You can also set the port to Spanning Tree disable if
you do not want that port to “participate”. The port is then put
directly into Forwarding State: meaning BPDUs cannot be sent out
the port, incoming BPDUs cannot be processed, and received traffic
can still be forwarded.
Spanning Tree Design
Avaya recommends that you consider the following standard
IEEE802.1D Guidelines when you design your network, no matter
which Spanning Tree mode you decide to use:
■
Assure core switches can be forced to be root bridges. For
per-VLAN Spanning Tree, the function of root bridge can be
shared among several core switches
■
When using standard timers assure the depth of the tree does
not exceed 7 bridges when a default bridge timer is used
■
Enable FAST START on all ports that include IPX and DNS
clients.