Alcatel-Lucent 1643 AMS Applications And Planning Manual page 190

Ethernet Overview
Spanning tree protocol (STP)
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Overview
The spanning tree protocol (STP) is a standard Ethernet method for eliminating loops
and providing alternate routes for service protection. Standard STP depends on
information sharing among Ethernet switches/bridges to reconfigure the spanning tree
in the event of a failure. The STP algorithm calculates the best loop-free path
throughout the network.
STP defines a tree that spans all switches in the network; it e.g. uses the capacity of
available bandwidth on a link (path cost) to find the optimum tree. It forces redundant
links into a standby (blocked) state. If a link fails or if a STP path cost changes the
STP algorithm reconfigures the spanning tree topology and may reestablish previously
blocked links. The STP also determines one switch that will be the root switch; all
leaves in the spanning tree extend from the root switch.
Maximum bridge diameter
The maximum bridge diameter is the maximum number of bridges between any two
hosts on the bridged LAN for any spanning tree configuration.
For TransLAN
Spanning tree example
The following example network serves to illustrate the principle how a spanning tree is
constructed.
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11-14
®
applications the maximum bridge diameter is 25 nodes.
LAN
Switch 2
2c
1b
Switch 1
1c
1a
LAN
Alcatel-Lucent - Proprietary
See notice on first page
2a
2b
3c
Switch 3
3b
3a
LAN
365-312-801R7.2
Issue 3, May 2007