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Cisco 3750 switch

Posted on 2014-08-13
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I just bought a used 3750 cisco switch and I wanted to know, how do I know if spanning tree is enabled, if not, how do I enable it?  I'm looking online at cisco's site, and there's so many options for spanning tree, that I'm not sure whether to use mst, pvst, or rapid-pvst, etc...

Any ideas.
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Question by:afacts
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Expert Comment

by:Shahnawaz Ahmed
ID: 40258794
Dear Afacts,

You can enable this feature by using the spanning-tree portfast interface configuration or the spanning-tree portfast default global configuration command.
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Expert Comment

by:Shahnawaz Ahmed
ID: 40258818
Commands Examples are below

1. Switch-A> (enable) show version
It will output the version of your switch

2. Switch-A> (enable) show port spantree 2/1
Port      Vlan  Port-State     Cost   Priority  Fast-Start  Group-Method
--------  ----  -------------  -----  --------  ----------  ------------
 2/1      1     forwarding        19        32  disabled

3. Switch-A> (enable) set spantree portfast 2/1 enable

4. Switch-A> (enable) show port spantree 2/1

Port      Vlan  Port-State     Cost   Priority  Fast-Start  Group-Method
--------  ----  -------------  -----  --------  ----------  ------------
 2/1      1     forwarding        19        32  enabled
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Author Comment

by:afacts
ID: 40258867
so do I have to enable spanning tree on each port?

Can't I just enable it on the entire switch?

When I did the show run, here's what it says about spanning tree:

!
spanning-tree mode pvst
spanning-tree extend system-id
!


So I think it's enabled, but not sure if it's using the best option or method.

So how do I know if it's enabled on all ports?
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Expert Comment

by:Shahnawaz Ahmed
ID: 40258925
Dear Afacts,
i don't  know this into deep however i can help you with some good informative articles on this, which might help.

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_55_se/commmand/reference/3750cr/cli3.html
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Shahnawaz Ahmed earned 2000 total points
ID: 40258944
Some more info i found for you.



Spanning Tree Protocol (STP) is enabled by default on modern switches. It is possible to disable or enable the Spanning Tree Protocol (STP) when required.

To enable Spanning Tree Protocol (STP) on an IOS based switch, use the "spanning-tree vlan vlan_number" command from global configuration mode as shown below.

omnisecu.com.switch01>
omnisecu.com.switch01>enable
omnisecu.com.switch01#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
omnisecu.com.switch01(config)#spanning-tree vlan 1
omnisecu.com.switch01(config)#exit
omnisecu.com.switch01#

To disable Spanning Tree Protocol (STP) on an IOS based switch use "no spanning-tree vlan vlan_number" command from global configuration mode as shown below.

Note: Never disable Spanning Tree Protocol (STP) if there is no valid reason to disable it. Disabling Spanning Tree Protocol (STP) can cause Broadcast Storms and Layer 2 Switching Loops, which can make your network down within a short span of time. Use with extreme care.

omnisecu.com.switch01>enable
omnisecu.com.switch01#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
omnisecu.com.switch01(config)#no spanning-tree vlan 1
omnisecu.com.switch01(config)#exit
omnisecu.com.switch01#
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Author Closing Comment

by:afacts
ID: 40258974
thanks, so it looks like it's already enabled, so I'll just leave it as such.
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Expert Comment

by:Shahnawaz Ahmed
ID: 40258976
Your welcome. Afacts.

Happy to assist you.
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Expert Comment

by:Jonathan Dunn
ID: 40483655
you might want to change the default to rapid spanning tree. Has some quicker convergence features
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