Before placing new Switch on the Network

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Feb 11th, 2009
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I'm about to place our new 3560 switch onto the network. There are 9 other cisco switches on this network. Is there anything I should check before placing the new switch on the network? Is it safe to just place it on the network? I don't wanna take the whole network down!

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Overall Rating: 5 (2 ratings)
adamclarkuk_2 Wed, 02/11/2009 - 02:05
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Hi Kaamil

If you are using VTP ( ie non transparent mode everywhere ), I would be checking all the relevent details about that ie domain / mode / version , if unsure, set it to vtp transparent mode.

Also check what spanning tree version you are running and if you have changed any of the priority's, check that this new switch wont take over as the root ( unless that's what you want).

kaamil.abrahams Wed, 02/11/2009 - 05:20
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What should I check for so that the new switch wont take over as the root? Where can I find out more about VTP? & Is there somewhere that I can check for all these commands?

adamclarkuk_2 Wed, 02/11/2009 - 07:02
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To check the status of VTP type the following:-

show vtp status

VTP Version : 2

Configuration Revision : 0

Maximum VLANs supported locally : 1005

Number of existing VLANs : 23

VTP Operating Mode : Transparent

VTP Domain Name :

VTP Pruning Mode : Disabled

VTP V2 Mode : Disabled

VTP Traps Generation : Disabled

MD5 digest : 0x90 0x18 0xBD 0x95 0xB5 0xE9 0x3A 0x17

Configuration last modified by at 0-0-00 00:00:00

More VTP info here

As for preventing the switch becoming the root, set the spanning tree priority to the highest as the lowest wins the election.

Set the priority to the highest 61440 for all vlans using :-

spanning-tree vlan 1-4094 priority 61440

Jon Marshall Wed, 02/11/2009 - 07:10
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In addition to Adam's posts

1) If you add a new switch and this switch is connected via a trunk link to your existing switches and all vlans are allowed on the trunk then there will be an STP reconvergence. You should add the switch out of hours or schedule downtime for it.

2) It's not clear whether you are running VTP Server/Client or not on your existing switches. To ensure that this new switch has a revision number of 0, on the switch

3560(config)# vtp mode transparent

then if you want it to be a vtp client just change it back to client mode ie.

3560(config)# vtp mode client

The above should be done before connecting the switch to the rest of your network.

As for becoming root, you can do as Adam suggested. A more long term approach is to pick 2 switches in your existing setup and make them root and secondary. That way you won't then have this issue again if you need to add a further switch.

Adding a switch to an existing network should always be done out of core production hours.


Leo Laohoo Wed, 02/11/2009 - 15:55
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Make sure the uplink port(s) is either trunk, routed or disable portfast (no spanningtree portfast).

Another thing, if you are unsure about what you're doing, implement this after hours.


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