Some comments below: ""dovelet"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Hi all, > > I have a question about Cisco Catalyst 3500XL switch with Gigastack in > Spanning Tree, and I hope someone can help me. I have a network like this: > > [Root] > SW1 ----- Gigastack (1)------ SW2 > |----------Gigastack (2) -----x--| > > I have 2 Cat.3500XL switches and use 2 gigastack cable to connect them. It > work fine and I found that the LED on Gigastack (1) is green while the > SW2-Gigastack (2) is in amber. I assume that the port on SW2-Gigastack (2) > is spanning tree blocking. Now, I want to install one more Cat.3500XL > switch. Then I disconnect the cable SW2-Gigastack (2). However, I found that > the network connection between the two switches are broken for about 50sec. > I think it is due to spanning tree re-learning.
CL: yes. this is the way spanning tree works. new links detected. STP runs. This is intentional, and is to ensure loop free topologies. this is alos the bane of network managers everywhere, for a lot of reasons. >Then I install a new Cat.3500XL (SW3) into the stack. > > [Root] > SW1 ----- Gigastack (1)------ SW2 > | > |----------Gigastack (2) -----SW3 > > However, I found that the network connection between SW1 and SW2 was broken > again for about 50 sec. The spanning tree re-learn again! CL: sounds about right. > > My questions are: > 1. Why is the spanning tree re-learn if I just disconnect the blocking link > at SW2-gigastack (2)? CL: becasue you have still introduced a change. i.e. the link in question disappears > 2. Why is the spanning tree re-learn if I install a new switch? (I am sure > SW1 is still the root bridge) CL: becasue you are still introducing a change. STP runs because there exists the possibility that the new switch introduces a loop. it is also possible that the new switch has a better priority and is supposed to become the root bridge. > 3. I want to enable spanning portfast on all of the gigastack port. However, > I wonder will it cause network loop if I connect the SW2 and SW3 with > Gigastack? CL: portfast is not a real good idea for ports connected to other switches. the whole idea of STP is to ensure loop free topologies. you are deliberately bypassing the process that ensures loop free when you enable portfast. the whole idea of portfast is geared towards workstations that time out, thinking they are not connected to a network, during the time the STP is running. > 4. As the SW3 is on loan, I need to replace it after several months. Is that > means, the network connection between SW1 and SW2 will be interrupt again? CL: yes. so do the work after hours, if this is an issue. > > Please help! CL: given waht appears to be a small and more or less controlled environment, you can disable spanning tree, if you think you can assure loop free in general. STP is there to protect you, but in some environments it may not be necessary. > > Thanks, > Dovelet Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=51454&t=51454 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
