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VLANS automatically being added to Switch

I am experiencing an issue I can't seem to get a grasp on.  I have VLANS being automatically configured on my switches and can't determine why this is happening.  I hope I provide enough information below, any suggestions on what could be happening here?

3745 (Edge Router) >>>> SF300 #1 (Distro Switch) >>>> SF300 #2 (Layer 3, CPE Switch)

3745 Native VLAN is 1

SF300 #1 Native VLAN is 3000

SF300 #2 Native VLAN is 1


FE3/1 = (, Connected to SF300 #1)

With Public IP Addresses passing through

And routes set

SF300 #1

FE/4 = 3000UP, 901T (Connected to 3745)  - changes to: FE/4 = 1UP, 13T, 901T, 3000T

FE/5 = 3000UP, 901T (Connected to SF300 #2) - changes to: FE/5 = 1UP, 13T, 901T, 3000T

SF300 #2

FE/8 = 901UP (, Connected to SF300 #1)

VLAN 1UP on all other ports with x.x.x.x as public IP

Route set for all traffic to go out

**** I am not having problems with data or traffic going through, I am however having an issue with the switches reconfiguring the VLANS.  When I plug something else into SF300 #1, the particular port I plug into changes from 3000U to 1UP, 13T, 901T, 3000T.  If I plug another SF300 #3 switch into SF300 #1 it switches the interface the same and when I plug anything into #3 that particular interface changes the same.

  • Small Business Switches

VLANS automatically being added to Switch

Hi Brian, this is a some sort of advertisement most likely through CDP. This is due to the macro detecting this configuration (or possibly confusing?) a configuration from an upstream device.

You can try disable CDP on the particular switch port to see if that fixes it or a bit more extreme, disable the switch macro.

Please mark answered for helpful posts

-Tom Please mark answered for helpful posts

VLANS automatically being added to Switch

Hello Brian,

I believe what is happening here has to do with Smartports.  When you plug in another switch, the 300 detects that and switches to the SmartPort profile for a switch, which is to set it as a trunk with all VLANs allowed.  When you unplug the other switch from the SG300 do the settings revert back?  If so that is Smartport working.

You can disable it per interface or for the entire switch.  Just note that when you disable it for the entire switch it will default all of the VLAN port settings, so you may just want to disable it for the switch ports. 

Let me know if that helps,

Christopher Ebert


SME - Network Support Engineer

Cisco Small Business Support Center

*please rate helpful posts*