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Cisco 2901 - Trunking Port/Vlan allowed Question

Posted on 2013-06-11
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Last Modified: 2013-07-22
Hey Guys,

I’ve got a  Cisco CISCO2901/K9 router which I’m wanting to configure the GI0/3/3 port to a trunking port and only allow vlan 1101 over the trunk.

The switchport is configured as a trunking port and is working fine. However when I use the command switchport trunk allowed vlan add 1101 it looks like it accepts it, but then doesn’t show up in the show interfaces trunk.

interface GigabitEthernet0/3/3
 description LINK_WAN
 switchport mode trunk
 no ip address


ROUTER#show interfaces trunk

Port      Mode         Encapsulation  Status        Native vlan
Gi0/0/0   on           802.1q         trunking      1
Gi0/3/3   on           802.1q         trunking      1

Port      Vlans allowed on trunk
Gi0/0/0   1-4094
Gi0/3/3   1-4094

Port      Vlans allowed and active in management domain
Gi0/0/0   1,399,1101
Gi0/3/3   1,399,1101

Port      Vlans in spanning tree forwarding state and not pruned
Gi0/0/0   1,399,1101
Gi0/3/3   1,399,1101
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Question by:supportemea
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Expert Comment

by:max_the_king
ID: 39237298
Hi,

i believe you need to add the following to interface configuration:

interface GigabitEthernet0/3/3
switchport trunk allowed vlan 1101
switchport mode trunk

hope this helps
max
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Expert Comment

by:max_the_king
ID: 39237303
please note that you should add in that command all vlans you want to go through trunk, otherwise it will pass only vlan 1101

i.e.:
interface GigabitEthernet0/3/3
switchport trunk allowed vlan 1,399,1101
switchport mode trunk

should you want to trunk the 3 vlans 1,399 and 1101

max
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by:supportemea
ID: 39237305
Hi Max,

Looks like it doesnt as I get the error

Command rejected: Bad VLAN allowed list. You have to include all default vlans, e.g. 1-2,1002-1005.
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max_the_king earned 500 total points
ID: 39237323
Hi,
yes it may happen, please read the following (trunk section):
http://www.cisco.com/en/US/products/hw/modules/ps2797/products_configuration_example09186a00808066b8.shtml#step2

hope this helps
max
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Expert Comment

by:max_the_king
ID: 39237329
however i wouldn't worry, you may want to have a look at this:
https://supportforums.cisco.com/thread/2167537

it is well explained
max
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Expert Comment

by:Don Johnston
ID: 39237396
I’ve got a  Cisco CISCO2901/K9 router which I’m wanting to configure the GI0/3/3 port to a trunking port and only allow vlan 1101 over the trunk.
If you only want to allow one VLAN, why do you want a trunk?  This defeats the whole point of a trunk in the first place.
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Expert Comment

by:BigPapaGotti
ID: 39237508
Try using the command below:

switchport trunk allowed vlan 1-1005,1101

This will specify the default vlans that need to be allowed as well as the only VLAN you want to traverse the link. Keep in mind that you need to enter this command under the appropriate interface for each side of the trunk's link.
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by:BigPapaGotti
ID: 39242656
Any updates
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by:BigPapaGotti
ID: 39260856
Any change/updates for us?
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Expert Comment

by:Don Johnston
ID: 39260877
You in a hurry or something? :-)
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