From: 401anil@gmail.com   
      
   I doubt 'why do we need a loop here?'   
      
   But if you have a loop within a switch then:    
      
   One of the ports will be blocked based on port priority as the Bridge ID is   
   same(both ports belong to the same switch). BPDUs will be sent on the   
   interface which is in forwarding state.   
      
   Determining port state is based on following order:   
   1. Lowest root bridge ID - Determines the root bridge   
   2. Lowest cost to the root bridge - Favors the upstream switch with the least   
   cost to root   
   3. Lowest sender bridge ID - Serves as a tie breaker if multiple upstream   
   switches have equal cost to root   
   4. Lowest sender port ID - Serves as a tie breaker if a switch has multiple   
   (non-Etherchannel) links to a single upstream switch   
      
   Here 1, 2, and 3 are same as this loop is within a switch. So it goes to the 3   
   condition.   
      
   Port ID is a 2Byte field, which consists of port-priority(4bits)   
   port-number(12bits).   
      
   If you don't configure port priority it takes the default priority and elect   
   the  highest port-number interface to forwarding state. In case if you want to   
   make any particular interface to forwarding mode you can configure   
   port-priority to the interfaces    
   based on your requirement.    
      
   This solution is also applicable to the topology where you have redundant   
   links between two switches and all are in same spanning tree group as   
   following topology:   
      
   +------+             +------+   
   |      |-------------|      |   
   |  A   |-------------|  B   |   
   |      |-------------|      |   
   +------+             +------+   
      
   Here A and B are two switches with 3 links between them. All these ports are   
   in same broadcast domain.   
      
   Thanks!   
      
   Anil A Kumar   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)