Foundry Configuration Guide for the FESX, FSX, and FWSX
7 - 18 © Foundry Networks, Inc. December 2005
Syntax: [no] fast port-span [exclude ethernet [<slotnum>/]<portnum> [ethernet [<slotnum>/]<portnum> | to
[<slotnum>/]<portnum>]]
To re-enable Fast Port Span on a port, enter a command such as the following:
FESX424 Router(config)# no fast port-span exclude ethernet 1
FESX424 Router(config)# write memory
This command re-enables Fast Port Span on port 1 only and does not re-enable Fast Port Span on other excluded
ports. You also can re-enable Fast Port Span on a list or range of ports using the syntax shown above this
example.
To re-enable Fast Port Span on all excluded ports, disable and then re-enable Fast Port Span by entering the
following commands:
FESX424 Router(config)# no fast port-span
FESX424 Router(config)# fast port-span
FESX424 Router(config)# write memory
Disabling and then re-enabling Fast Port Span clears the exclude settings and thus enables Fast Port Span on all
eligible ports. To make sure Fast Port Span remains enabled on the ports following a system reset, save the
configuration changes to the startup-config file after you re-enable Fast Port Span. Otherwise, when the system
resets, those ports will again be excluded from Fast Port Span.
802.1W Rapid Spanning Tree (RSTP)
Foundry’s earlier implementation 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 Foundry 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:
• 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.
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