3-70 Sun Fire B1600 Blade System Chassis Switch Administration Guide •June 2003
3.3.4 Spanning Tree Algorithm Configuration
The Spanning TreeAlgorithm (STA) can be used to detect and disable network
loops, and to provide backup links between switches, bridges or routers. This allows
the switch to interact with other bridging devices (that is, an STA-compliant switch,
bridge or router) in your network to ensure that only one route exists between any
two stations on the network, and provide backup links which automatically take
over when a primary link fails.
The spanning tree algorithms supported by this switch include these versions:
■STP – Spanning TreeProtocol (IEEE 802.1D)
■RSTP – Rapid Spanning TreeProtocol (IEEE 802.1w)
RSTP is a general replacement for the slower,legacy STP. RSTP achieves must faster
reconfiguration (around one tenth of the time required by STP) by reducing the
number of state changes before active ports start learning, predefining an alternate
route that can be used when a node or port fails, and retaining the forwarding
database for ports insensitive to changes in the tree structure when reconfiguration
occurs.

3.3.4.1 Configuring Basic STA Settings

Global settings apply to the entire switch.
Note the following points about basic STA settings:
■Rapid Spanning Tree Protocol
RSTP supports connections to either STP or RSTP nodes by monitoring the
incoming protocol messages and dynamically adjusting the type of protocol
messages the RSTP node transmits:
■STP Mode – If the switch receives an 802.1D BPDU (STP BPDU) after a port’s
migration delay timer expires, the switch assumes it is connected to an 802.1D
bridge and starts using only 802.1D BPDUs.
■RSTP Mode – If RSTP is using 802.1D BPDUs on a port and receives an RSTP
BPDU after the migration delay expires, RSTP restarts the migration delay
timer and begins using RSTP BPDUs on that port.
When configuring basic STAsettings through the web interface or CLI, the following
global parameters can be configured:
■Enable Spanning Tree – The currentoperational status of STA on the switch.
■Spanning TreeProtocol – The type of spanning tree used on the switch:
■STP: Spanning TreeProtocol (IEEE 802.1D). When this option is selected, the
switch will use RSTP set to STP forced-compatibility mode.
■RSTP: Rapid Spanning TreeProtocol (IEEE 802.1w).