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spanning tree on router in gns3

Posted on 2013-06-02
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Last Modified: 2013-06-22
I am simulating my router as a layer 3 switch (configure slot with NM-16ESW). I have vlan10 and vlan25 and I am trying to check my spanning tree configuration. I don't see any statement in my config file like "spanning-tree mode pvst" like in the real switch. Do I have to enable the spanning-tree? If yes how? Thanks
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Question by:leblanc
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Expert Comment

by:giltjr
ID: 39216031
Which L3 device are you simulating?

What level of IOS?

Typically spanning tree is enabled by default.  What happens when you issue "show spanning-tree"?
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Author Comment

by:leblanc
ID: 39216380
I am trying to simulate a 3750.

IOS 12.4(25c)

Below is the sh span output, as you can see, everything is in the forwarding state.
sw2#sh spa


 VLAN10 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, address cc04.0838.0001
  Configured hello time 2, max age 20, forward delay 15
  Current root has priority 32768, address cc02.0838.0001
  Root port is 2 (FastEthernet0/1), cost of root path is 19
  Topology change flag set, detected flag not set
  Number of topology changes 1 last change occurred 00:00:25 ago
          from FastEthernet0/1
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0, aging 300

 Port 2 (FastEthernet0/1) of VLAN10 is forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.2.
   Designated root has priority 32768, address cc02.0838.0001
   Designated bridge has priority 32768, address cc02.0838.0001
   Designated port id is 128.2, designated path cost 0
   Timers: message age 1, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   BPDU: sent 3, received 23

 Port 4 (FastEthernet0/3) of VLAN10 is forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.4.
   Designated root has priority 32768, address cc02.0838.0001
   Designated bridge has priority 32768, address cc04.0838.0001
   Designated port id is 128.4, designated path cost 19
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   BPDU: sent 25, received 1


 VLAN25 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, address cc04.0838.0002
  Configured hello time 2, max age 20, forward delay 15
  Current root has priority 32768, address cc02.0838.0002
  Root port is 2 (FastEthernet0/1), cost of root path is 19
  Topology change flag set, detected flag not set
  Number of topology changes 1 last change occurred 00:00:31 ago
          from FastEthernet0/1
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0, aging 300

 Port 2 (FastEthernet0/1) of VLAN25 is forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.2.
   Designated root has priority 32768, address cc02.0838.0002
   Designated bridge has priority 32768, address cc02.0838.0002
   Designated port id is 128.2, designated path cost 0
   Timers: message age 2, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   BPDU: sent 3, received 26

 Port 4 (FastEthernet0/3) of VLAN25 is forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.4.
   Designated root has priority 32768, address cc02.0838.0002
   Designated bridge has priority 32768, address cc04.0838.0002
   Designated port id is 128.4, designated path cost 19
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   BPDU: sent 28, received 1


 VLAN200 is executing the ieee compatible Spanning Tree protocol
  Bridge Identifier has priority 32768, address cc04.0838.0003
  Configured hello time 2, max age 20, forward delay 15
  Current root has priority 32768, address cc02.0838.0003
  Root port is 2 (FastEthernet0/1), cost of root path is 19
  Topology change flag set, detected flag not set
  Number of topology changes 1 last change occurred 00:00:37 ago
          from FastEthernet0/1
  Times:  hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
  Timers: hello 0, topology change 0, notification 0, aging 300

 Port 2 (FastEthernet0/1) of VLAN200 is forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.2.
   Designated root has priority 32768, address cc02.0838.0003
   Designated bridge has priority 32768, address cc02.0838.0003
   Designated port id is 128.2, designated path cost 0
   Timers: message age 1, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   BPDU: sent 3, received 30

 Port 4 (FastEthernet0/3) of VLAN200 is forwarding
   Port path cost 19, Port priority 128, Port Identifier 128.4.
   Designated root has priority 32768, address cc02.0838.0003
   Designated bridge has priority 32768, address cc04.0838.0003
   Designated port id is 128.4, designated path cost 19
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   BPDU: sent 32, received 1
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LVL 57

Expert Comment

by:giltjr
ID: 39217382
That show that spanning tree is enable.

According to the below PVST+ is default on 3750 and show run/start will not show default values.

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_55_se/commmand/reference/cli3.html#wp1946050
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Author Comment

by:leblanc
ID: 39217466
I am running a 3640 router as a layer 3 switch. I don't have a 3750 switch in GNS3. Thx
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Accepted Solution

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giltjr earned 500 total points
ID: 39217547
From your prior post: "I am trying to simulate a 3750."  We can only answer based on what you state.

But search on 3640 and NM-ESW16 I found the following post which implies that PVST+ is the only mode and you can't change it.  Search on PVST+.

http://www.saeedpazoki.com/setup-a-cisco-switch-lab-with-gns3/
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