[c-nsp] Spanning-Tree question

[Aaron R]

Separate VLANs (not overlapping) The four switches are connected for
redundancy purposes. Business unit A has resources upstream that business
unit B must be able to access (but still needs to remain separate
administratively)

As the shabby diagram depicts, each business unit switch is trunked together
to share vlan info but the links between business unit switches are access
links in separate vlans.

The problem I believe im facing here is the fact that portfast was enabled
(bad mistake) and causing the ports to forward straight away and not listen
to bpdu's in order to block one of the links. 


Cheers,

Aaron.

-----Original Message-----
From: Tom Sands [mailto:tsands at rackspace.com] 
Sent: Friday, February 01, 2008 9:36 PM
To: Aaron R
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Spanning-Tree question

Though you using 2 different VTP domains/VLAN databases, are the VLANs 
per business unit at least unique so the VLAN databases don't have 
overlapping VLANs?

What's the purpose of interconnecting the 4 switches?

What are the connections between the 4 switches? access port (same vlan 
on each side or every switch)? trunk? L3?




------------------------------------------------------
Tom Sands			  				
Chief Network Engineer				
Rackspace 	    	
(210)312-4391	   	
------------------------------------------------------

Aaron R wrote:
> Hi Guys, 
> 
>  
> 
> Ive got a problem that I am hoping someone can have a look at. I currently
> have four 3750's. Two belonging to one business unit and two belonging to
> another. Each group of switches is running a separate VTP domain / VLAN
> database.
> 
> I am running PVST however when I connect the final link between the four
> switches there is a loop and spanning tree doesn't block any of the ports.
> Would anyone have any clue as to why this would be happening? Could it
have
> something to do with the link between the Business units being on separate
> VLANs? We don't want the possibility of VLAN corruption occurring hence
the
> different VTP domains. Currently I am shutting down one of the uplink
ports
> to Business A to remedy this problem. Please see the diagram below. 
> 
>  
> 
> Cheers,
> 
>  
> 
> ------------------------                         ------------------------
> 
> | 3750 Switch 1  |------- Trunk ------ | 3750 Switch 2  |
> 
> |  Business A     |                        |  Business A     |
> 
> -------------------------                        -------------------------
> 
>            |   VL 50                                   |   VL 50
> 
> 
>            |                                              |
> 
>            |   VL 100                                 |    VL 100
> 
> 
> ------------------------                         ------------------------
> 
> | 3750 Switch 3  |------- Trunk ------ | 3750 Switch 4  |
> 
> |  Business B     |                        |  Business B     |
> 
> -------------------------                        -------------------------
> 
>  
> 
>  
> 
> Aaron.
> 
>  
> 
>  
> 
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
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> 


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