Check out the new portfast bpdu guard feature. It can shut down ports that
have portfast enabled when detecting bpdus on the line.
Keith
-----Original Message-----
From: McCallum, Robert [mailto:[EMAIL PROTECTED]]
Sent: Thursday, March 01, 2001 10:44 AM
To: 'John Chang'; 'Ccielab' (E-mail); Cisco@Groupstudy. Com (E-mail)
Subject: RE: Portfast
No,
The problem occurs if he creates a loop i.e. you have a main switch a cable
from the main switch goes to user A. User A decides to connect a hub and a
few terminals - Outcome fine. User B then says hey user A can you access
those terminals and the main network. User A says yeah how do you want to
connect? User A says yes and inadvertently patches his own pc and the
original connection that was from him to the main switch outcome is now main
switch has 2 connections to the minihub. NOW spanning tree goes oh my and
recalculates - outcome 30 second outage for everyone on that vlan. Then the
users go home, switch off their kit and go to the pub.
Next day..... The mini hub is switched back on - because portfast is enabled
the ports go whoosh straight into forwarding mode - result - spanning tree
goes oh my!! and recalculates.
Outcome ------ You and every other support member run about like loonies
trying to find this fault which occurs only when the user decides to switch
on his equipment.
-----Original Message-----
From: John Chang [mailto:[EMAIL PROTECTED]]
Sent: 01 March 2001 15:34
To: McCallum, Robert
Subject: RE: Portfast
Let me see if I got this correct. If he only connects one mini-hub or
mini-switch it is OK to have portfast on on the main switch. If he then
connects another mini-hub or mini-switch onto the first mini-hub or
mini-switch than there will be a problem. But when you connect 2 mini-hubs
aren't you just extending the amount of ports and in a sense there is only
one virtual mini-hub?
At 03:24 PM 3/1/2001 +0000, you wrote:
>yes, but only if he then connects another link to another hub / switch and
>causes a bridging loop.
>
>-----Original Message-----
>From: John Chang [mailto:[EMAIL PROTECTED]]
>Sent: 01 March 2001 15:08
>To: [EMAIL PROTECTED]
>Subject: Portfast
>
>
>In the below website it says not to have portfast on if you connect
>switches, hubs, or routers. I understand that point but what if a user
>connected a mini-hub (Ex. Linksys EtherFast 8-Port 10/100 Desktop Hub)
>or unmanaged mini-switch (Ex. Farallon NetLINE 10/100 switch) so that he
>could connect multiple computers. Would this cause any problems? Thank
>you!
>
>
>http://www-1.cisco.com/warp/public/473/12.html
>
>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.
>
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