3 Replies Latest reply: Mar 31, 2012 9:02 AM by Elvin Arias RSS

    STP PORT ROLES VS RSTP PORT ROLES

    pepsi

      VLAN0003

        Spanning tree enabled protocol ieee

        Root ID    Priority    32768

                   Address     0018.b103.4c00

                   Cost        4

                   Port        13 (GigabitEthernet1/0/13)

                   Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

       

        Bridge ID  Priority    32771  (priority 32768 sys-id-ext 3)

                   Address     001f.6ded.0300

                   Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

                   Aging Time 300

       

      Interface        Role Sts Cost      Prio.Nbr Type

      ---------------- ---- --- --------- -------- -------------------------

      Gi1/0/3          Desg FWD 4         128.3    P2p

      Gi1/0/6          Desg FWD 4         128.6    P2p

      Gi1/0/13         Root FWD 4         128.13   P2p

      Gi1/0/14        Altn BLK 4         128.14   P2p

      Gi1/0/15         Altn BLK 4         128.15   P2p

      Gi1/0/16         Desg FWD 4         128.16   P2p

      Gi1/0/17         Desg FWD 4         128.17   P2p

      Gi1/0/18         Desg FWD 4         128.18   P2p

       

       

      Sh Run Command output

      spanning-tree mode pvst

       

      I have multiple confusions in the above output.

       

      1. In First line it shows (Spanning tree enabled protocol ieee, where as in "sh run" command it shows "spanning-tree mode pvst" which is not IEEE, its Cisco proprietary?

       

      2. If at all PVST is running how the "Alternate" Port role is there and how the Forward Delay is 15 Sec (it looks like its running Rapid PVST)

       

      The above output I have checked in all my switches and it looks to be same.

       

      Please help.

        • 1. Re: STP PORT ROLES VS RSTP PORT ROLES
          Elvin Arias

          1- The default Catalyst STP mode is PVST+ and you can identify that by seeing that there is an instance of STP per VLAN.

           

          2- Since the switch is running PVST+ it must be subject to the forward delay and max_age timers. The only case that this STP flavor is not subject to these timers is when the UplinkFast (for direct failures), and BackboneFast (for indirect failures) features are globally enabled on the switch. Alternate is just showing, because Cisco's Catalyst switches internally see the ports (blocking ports) as Alternate ports.

           

          Elvin

          • 2. Re: STP PORT ROLES VS RSTP PORT ROLES
            pepsi

            Thanks Elvin for quick response !

            1. I agree the default STP mode is PVST+ but its not IEEE, then why it is showing Spanning tree enabled protocol ieee.

             

            2. The default forward delay in PVST+ is 30 sec, where as shown in the output is 15 Sec. For "Alternate" this could be the true.


            • 3. Re: STP PORT ROLES VS RSTP PORT ROLES
              Elvin Arias

              Yes, it's showing 15, but the listening and learning states have a 15 seconds of calculation, so in total you have 30 seconds, 15 for listening plus 15 for learning. Another clarification is that RSTP uses a 6 seconds for the max_age timer, and is not subject to the forward delay like older STP versions. Don't be bothered by the "Spanning tree enabled protocol ieee" message, since you know that the internal STP operation is not the like classic 802.1D, but PVST+.

               

              Elvin