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Community Member

4506 Vlan mismatch error

Hello ,

I've a cat 4506 and one of the 100Base-FX port was assigned to a vlan 10 say it is a port number 3/36 . Now , I have made this port as trunk (set trunk 3/36 on dot1q ) .After connecting a 2950 Switch with this port , I'm getting Vlan mismatch error on 2950 side . At 4506 side , it gives * mark for 3/36 port which is a conflict . I want to remove this port from Vlan 10 and make as a trunk port. This Switch is a VTP client .Will this command (clear vlan 10 3/36 ) resolve conflict problem .


Community Member

Re: 4506 Vlan mismatch error

When you create a trunk connection, the ports at each end need to be on the same vlan. So to correct your problem, you need to set the port on your 2950 to vlan 10.

Another think that you could do is that the port on your 2950 is probably on vlan 1. Then you need to set your port on the 4506 to vlan 1 and that also fix your problem.

on 4506: set vlan 1 3/36 (CatOS)

or if your are running IOS do the following:

config t

interface fastethernet 3/36

switchport access vlan 1


wr mem

Re: 4506 Vlan mismatch error


to be exact we are talking about 802.1q native VLAN problem.

Native VLAN frames are sent untagged on 802.1q trunk.

So you need to configure the same VLAN as native on both trunk sides.

Default value is VLAN1.

But is you had assigned a port to VLAN10 on Cat 4506 and then made the port a 802.1q trunk, the native VLAN is VLAN10 on the trunk.

(This is an old Cisco native VLAN definition, used on CatOS switches: Native VLAN is the VLAN to which the port returns when stops working as a trunk.)

There is no special command for native VLAN configuration on 4506 trunk, "set VLAN 10 " is used instead.

But there is a different situation on Cat2950 (genarally IOS based) switches:

You can use

conf t

int fa 0/y

switchport trunk native vlan 10


But switchport access vlan 1 won't help you.

Generally you've got two possibilities:

a) change native VLAN on 2950 trunk port to VLAN10

(switchport trunk native vlan 10)


b) move native VLAN on 4506 trunk port back to VLAN1

(set vlan 1 3/36)



Community Member

Re: 4506 Vlan mismatch error

Thanks Milan.I would go for option "b" i.e assigning the port to Vlan 1(My native Vlan is Vlan1) on 4506 side.

What should I do at other end (2950 side) ?. Should I make that port say port number 25 as trunk (switchport mode trunk ) or assign it to Vlan1 ( Swithport access Vlan1)


Re: 4506 Vlan mismatch error

If everything else is left default, simply

switchport mode trunk

BTW: "Switchport access Vlan1" has no role while the port is in trunk mode.

This is a different behaviour between IOS and CatOS switches.



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