Brocade FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide - Manual (Page 271)

STP instance owned by VLAN 2
Global STP (IEEE 802.1D) Parameters:
VLAN Root Root Root Prio Max He- Ho- Fwd Last Chg Bridge
ID ID Cost Port rity Age llo ld dly Chang cnt Address
Hex sec sec sec sec sec
2 8000000011111111 0 Root 8000 20 2 1 15 29596 0 000011111111
Port STP Parameters:
Port Prio Path State Fwd Design Designated Designated
Num rity Cost Trans Cost Root Bridge
Hex
1/1/1 80 4 LISTENING 0 0 8000000011111111 8000000011111111
Syntax: show span vlan vlan-id fast-uplink-span
The VLAN vlan-id parameter displays Fast Uplink Span information for the specified VLAN.
802.1W Rapid Spanning Tree (RSTP)
Earlier implementation by Brocade of Rapid Spanning Tree Protocol (RSTP), which was 802.1W Draft
3, provided only a subset of the IEEE 802.1W standard; whereas the 802.1W RSTP feature provides
the full standard. The implementation of the 802.1W Draft 3 is referred to as RSTP Draft 3.
RSTP Draft3 will continue to be supported on Brocade devices for backward compatibility. However,
customers who are currently using RSTP Draft 3 should migrate to 802.1W.
The 802.1W feature provides rapid traffic reconvergence for point-to-point links within a few
milliseconds (0 - 500 milliseconds), following the failure of a bridge or bridge port. This reconvergence
occurs more rapidly than the reconvergence provided by the 802.1D Spanning Tree Protocol (STP)) or
by RSTP Draft 3.
NOTE
This rapid convergence will not occur on ports connected to shared media devices, such as hubs. To
take advantage of the rapid convergence provided by 802.1W, make sure to explicitly configure all
point-to-point links in a topology.
The convergence provided by the standard 802.1W protocol occurs more rapidly than the convergence
provided by previous spanning tree protocols because of the following:
• Classic or legacy 802.1D STP protocol requires a newly selected Root port to go through listening
and learning stages before traffic convergence can be achieved. The 802.1D traffic convergence
time is calculated using the following formula.
2 x FORWARD_DELAY + BRIDGE_MAX_AGE.
If default values are used in the parameter configuration, convergence can take up to 50 seconds. (In
this document STP will be referred to as 802.1D.)
• RSTP Draft 3 works only on bridges that have Alternate ports, which are the precalculated "next best
root port". (Alternate ports provide back up paths to the root bridge.) Although convergence occurs
from 0 - 500 milliseconds in RSTP Draft 3, the spanning tree topology reverts to the 802.1D
convergence if an Alternate port is not found.
• Convergence in 802.1w bridge is not based on any timer values. Rather, it is based on the explicit
handshakes between Designated ports and their connected Root ports to achieve convergence in
less than 500 milliseconds.
Bridges and bridge port roles
A bridge in an 802.1W rapid spanning tree topology is assigned as the root bridge if it has the highest
priority (lowest bridge identifier) in the topology. Other bridges are referred to as non-root bridges.
802.1W Rapid Spanning Tree (RSTP)
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