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This Question is Not Answered 1 Correct Answer available (4 pts) 2 Helpful Answers available (2 pts)
1309 Views 3 Replies Latest reply: Mar 31, 2012 9:02 AM by Elvin Arias RSS

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STP PORT ROLES VS RSTP PORT ROLES

Mar 31, 2012 8:16 AM

pepsi 2 posts since
Oct 8, 2010

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.

  • Elvin Arias 2,505 posts since
    Mar 12, 2010
    Currently Being Moderated
    1. Mar 31, 2012 8:38 AM (in response to pepsi)
    Re: STP PORT ROLES VS RSTP PORT ROLES

    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

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  • Elvin Arias 2,505 posts since
    Mar 12, 2010
    Currently Being Moderated
    3. Mar 31, 2012 9:02 AM (in response to pepsi)
    Re: STP PORT ROLES VS RSTP PORT ROLES

    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

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