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gns3 - switchport trunk allow vlan error

Posted on 2016-11-04
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Last Modified: 2016-11-05
I am using GNS3 and am trying to have only one vlan on the trunk. I did the command below and I got an error. Then I tried to remove the existing VLANs but it did not remove them from the vlan db. Any thoughts? Thx

sw2(config-if)#switchport trunk allowed vlan 255
Command rejected: Bad VLAN allowed list. You have to include all default vlans, e.g. 1-2,1002-1005.
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Question by:leblanc
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Predrag earned 400 total points
ID: 41875163
In some old Cisco IOS versions you had to include VLANs 1002-1005 on trunks (and also VLAN 1 - if I remember correctly), but typically that's not the case anymore. Most likely problem is with Ethernet card inserted in router that you are using to emulate switch since GNS3 does not emulate switches (at least not when I checked it last time).

VLANs 1002 - 1005 are by default present for historical purpose (FDDI and token ring) on switches and can't be deleted. Don't worry about it, you can safely ignore that message for production. For testing purpose use:

sw2(config-if)# switchport trunk native vlan 255
sw2(config-if)# switchport trunk allowed vlan 1,255,1002-1005
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by:Niten Kumar
Niten Kumar earned 100 total points
ID: 41875166
Note: VLANs 1 and 1002 through 1005 are reserved VLANs and cannot be removed from any trunk link.

To add a VLAN to the trunk, issue the
switchport trunk allowed vlan add vlan-list

Open in new window

command.

sw2(config-if)#switchport trunk allowed vlan add 255

Open in new window


You can simulate switches really nicely with IOU.  Refer to the following link.

http://letusexplain.blogspot.com/2015/07/cisco-iou-l2-l3-lab-with-gns3-switching.html
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Expert Comment

by:Predrag
ID: 41875167
Niten Kumar, those VLANs can be removed from trunks, no problems with that.
Even Packet tracer will not argue about that (at least with 3560):

Switch(config-if)#switchport trunk allowed vlan 10
Switch(config-if)#do sh int trunk
Port        Mode         Encapsulation  Status        Native vlan
Gig0/1      on           802.1q         trunking      1

Port        Vlans allowed on trunk
Gig0/1      10

Switches can be emulated in UNL also (not sure about etherchannel, but I did not watch any videos so far). But, as a first impression, I like the tool (although did not waste too much time with it and just tested simple things, I am still getting familiar with it).
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by:leblanc
ID: 41875636
When you configure the VLAN, it is added automatically to the trunk.
The command sw2(config-if)# switchport trunk allowed vlan 1,255,1002-1005 worked. It looks like with the swithcing module I use for the router, you have to manually allow those default VLANs. Thx
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