Catalyst 3750 port fast configuration

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Jul 2nd, 2004
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I'm setting up a Catalyst 3750 and I'm attempting the configuration myself. I'm a beginner just getting started with Cisco products. The initial configuration went well. A Cisco reseller informed me that I should set up port fast on the switch. What is that and how do I configure port fast?

Thanks for any help.


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Georg Pauwen Fri, 07/02/2004 - 11:18
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Hello Jeff,

portfast is a feature that lets access ports bypass the spanning tree process. The idea is that access ports, that is, ports with endstations (and not switches) attached do not need to participate in the spanning tree process because they can never create a loop in the network. By turning on portfast (with the interface command ´spanning-tree portfast), the port is available and online right away, rather than going through the various spanning-tree stages, which take about 50 seconds. So what your reseller is saying is that you should enable that feature on all your access ports.

Here is the ´official´ Cisco explanation:

Understanding How PortFast Works

STP PortFast causes a Layer 2 LAN interface configured as an access port to enter the forwarding state immediately, bypassing the listening and learning states. You can use PortFast on Layer 2 access ports connected to a single workstation or server to allow those devices to connect to the network immediately, instead of waiting for STP to converge. Interfaces connected to a single workstation or server should not receive bridge protocol data units (BPDUs). If an interface connected to a single workstation or server receives a BPDU, STP puts the interface into the blocking state.


Note: Because the purpose of PortFast is to minimize the time that access ports must wait for STP to converge, it is effective only when used on access ports. If you enable PortFast on a port connected to a switch, you might create a spanning tree loop.


Caution: Use PortFast only when connecting a single end station to a Layer 2 access port; otherwise, you might create a network loop.



l.mallon Mon, 07/05/2004 - 02:26
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The easiest way is to select a portrange, otherwise you have to do the entry 12,24 or 48 times.

Do mind that the ports must have an endpoint connected. (E.G. PC Printer).

Prashanth Krishnappa Tue, 07/06/2004 - 04:51
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You might want to use the Macro command "switchport host" which enables portfast, disables channeling and trunking


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