Trunking vlan filtering

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Amit Singh Mon, 05/28/2007 - 08:37
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You can only use" switchport trunk allowed vlan "command to achieve the same. You need a combination of switchport allowed/remove commands only when you want to remove some of the vlans from the trunk and allow some of the vlans simultaneously.

HTH,please rate if it does.

-amit singh

Amit Singh Mon, 05/28/2007 - 09:09
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Native vlan is enabled on Cisco switches by default and Vlan1 is the native vlan. The native vlan is used to carry untagged frames across a trunk link.You will not be able to form a trunk if the native vlan is different on the trunk links. They have to be same on both the sides.

-amit singh

ankbhasi Mon, 05/28/2007 - 08:39
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Hi Friend,

On IOS switches if you just allow vlans that will take care of your requirement and no need to specifically clear other vlans first

Switch#sh run int gig1/0/23

Building configuration...

Current configuration : 137 bytes


interface GigabitEthernet1/0/23

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 22-26

switchport mode trunk


Switch#sh int gig1/0/23 switchport

Ankur_Desk_Switch#sh int gig1/0/23 switchport

Name: Gi1/0/23

Switchport: Enabled

Administrative Mode: trunk

Operational Mode: trunk

Administrative Trunking Encapsulation: dot1q

Operational Trunking Encapsulation: dot1q

Negotiation of Trunking: On

Access Mode VLAN: 1 (default)

Trunking Native Mode VLAN: 1 (default)

Administrative Native VLAN tagging: enabled

Voice VLAN: none

Administrative private-vlan host-association: none

Administrative private-vlan mapping: none

Administrative private-vlan trunk native VLAN: none

Administrative private-vlan trunk Native VLAN tagging: enabled

Administrative private-vlan trunk encapsulation: dot1q

Administrative private-vlan trunk normal VLANs: none

Administrative private-vlan trunk private VLANs: none

Operational private-vlan: none

Trunking VLANs Enabled: 22-26 <<<---------



*Pls rate all helpfull post

s.arunkumar Mon, 05/28/2007 - 22:21
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afaik, vlan 1 is management vlan and native vlan by default.

yes all the ports are in vlan 1 by default

in trunking if isl method is used then native vlan need not to be same.(and cisco s/w by default uses isl)

but with 802.1q trunking the native vlan packs as send its a must that native vlan on both end be the same...




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