Alcatel-Lucent 1643 AMS - Spanning tree protocol (STP)

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 for example, 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
®
applications the maximum bridge diameter is 25 nodes.
Spanning tree example
The following example network serves to illustrate the principle how a spanning tree is
constructed.
LAN
1a 3a
3b
3c
1c
1b
2c
2b
2a
Switch 1
Switch 2
Switch 3
LAN
LAN
Traffic provisioning
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365-312-807R7.2
Issue 4, May 2007
Alcatel-Lucent - Proprietary
See notice on first page
8-45