I quote directly from CCO: (http://www.cisco.com/warp/public/473/12.html)
If you are connecting a workstation or a server with a single NIC card to a
switch port, this connection cannot create a physical loop. These
connections are considered leaf nodes. There is no reason to make the
workstation wait 30 seconds while the switch checks for loops when the
workstation cannot cause a loop. So, Cisco added a feature named "portfast"
or "fast-start," which means the STP for this port will assume that the port
is not part of a loop and will immediately move to the forwarding state,
without going through the blocking, listening, or learning states. This
command does not turn STP off. It just makes STP skip a few (unnecessary in
this circumstance) steps in the beginning on the selected port.
Note: The portfast feature should never be used on switch ports that connect
to other switches, hubs, or routers. These connections may cause physical
loops and it is very important that spanning tree go through the full
initialization procedure in these situations. A spanning tree loop can bring
your network down. If portfast is turned on for a port that is part of a
physical loop, it can cause a window of time where packets could possibly be
continuously forwarded (and even multiply) in such a way that the network
cannot recover.
Cheers!
Roman
-----Original Message-----
From: Curtis Call [mailto:[EMAIL PROTECTED]]
Sent: Monday, December 11, 2000 6:35 PM
To: [EMAIL PROTECTED]
Subject: RE: cisco 3524 XL EN problem
Turning on portfast on a port with more than one host connected via a hub
will cause no problems with loops. The Hub is solely a layer one
connecting device so it is impossible for it to cause STP problems. If you
had a switch or a bridge connected to that port then you would have a
problem, but a hub would be fine.
At 03:12 PM 12/11/00 -0600, you wrote:
>This bears clarification...
>
>The port immediately goes into a forwarding state, bypassing the listening
>and learning states. However, it will learn the stations MAC address
>immediately
>on the first packet that the station sends. You say "at a later time" and
I
>think
>that is a little misleading. Also, it should be noted that this should
only
>be used when the switch port is connected to ONE host. If portfast is
>enabled on
>a port connecting to more than one host (i.e.- a hub with multiple servers)
>then switch
>loops will likely be the result.
>
>Roman
>
>-----Original Message-----
>From: Roan, Wayne [mailto:[EMAIL PROTECTED]]
>Sent: Monday, December 11, 2000 12:41 PM
>To: '[EMAIL PROTECTED]'
>Subject: RE: cisco 3524 XL EN problem
>
>
>You may need to enable portfast access. This will allow the computer to
>transmit data immediately and the switch will learn the MAC address at a
>later time. It will however broadcast data coming to your port on all
ports
>it does not know the MAC address for until it learns your computer's MAC
>address.
>
>-----Original Message-----
>From: atif [mailto:[EMAIL PROTECTED]]
>Sent: Monday, December 11, 2000 9:14 AM
>To: cisco group study
>Subject: cisco 3524 XL EN problem
>Importance: High
>
>
>i have installed a cisco 3524 xl en switch, i am facing a weird kind of =
>problem i hope u guys will help me solve this problem.
>the problem is that when a pc is connecte to switch for the 1st time it =
>takes about 4 to 5 minutes for the switch to communicate with the =
>machine.The led on both sides shows green light even when its not =
>communicationg and the ping request is timed out.
>then after that it takes about 1 minute for computer to see the switch =
>if we take the connecter out of the switch and inserts again.
>now todays it happened that after the weekend when computers were =
>started some were communicating and many were not and all leds were =
>showing green lights and after one hour or so every thing was =
>normalized.
>i havent seen this sort of problem before, this switch at the moment is =
>running at default configuration and connected to a router to a vsat =
>link.
>i havent assigned ip add info so far , can this be a problem( i dont =
>think so).=20
>can any body figure it out what is the problem,
>is something wrong with cabling,switch or NIC.
>
>atif
>
>
>_________________________________
>FAQ, list archives, and subscription info:
>http://www.groupstudy.com/list/cisco.html
>Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
>
>_________________________________
>FAQ, list archives, and subscription info:
>http://www.groupstudy.com/list/cisco.html
>Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
>
>_________________________________
>FAQ, list archives, and subscription info:
>http://www.groupstudy.com/list/cisco.html
>Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
_________________________________
FAQ, list archives, and subscription info:
http://www.groupstudy.com/list/cisco.html
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
_________________________________
FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
