[c-nsp] Spanning-Tree question

[Aaron R]

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.