vlan 1 minimization and native vlan

Answered Question
Dec 8th, 2011

When I connect two switches using trunk ports, by default Vlan1 will be the native vlan for the trunk ports. The recommended practice is to assign a non default vlan vlan1 and also no to use management vlan as native vlan. Is it mandatory to define a native vlan for trunk ports?

What is vlan 1 minimization?

I have this problem too.
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Correct Answer by Beetlejuice01 about 2 years 4 months ago

If you intend, per interface you doesn't need to configure the command native vlan, you only need the command switchport trunk encapsulation dot1q, switchport mode trunk, and it works, but the vlan allowed on this trunk is all from 1 to 4095, and the native is implicit vlan 1. If switch on both side are cdp enabled on trunk interface, and different natvie is specified on one of the switch you will see this error, %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered, and need to see the configuration and change tha native on one of the side.

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Beetlejuice01 Fri, 12/09/2011 - 00:38

Vlan 1 is the default vlan for Cisco, vlan1 is sent over trunk links untegged so without a "badge" who say wich vlan is. If on a switch the default vlan is 1 and on the other side of link vlan2 is native both are untegged and traffic from the "pipe" vlan 1 go in 2 so if someon sent frame untagged that come in native vlan over trunk... so doesn't use native as managementVlan. Native can also be sent tagged with command vlan dot1q tag native in global config.

avilt Fri, 12/09/2011 - 01:00

Understood. However is it mandatory to define a native vlan for trunk ports?

Correct Answer
Beetlejuice01 Fri, 12/09/2011 - 01:11

If you intend, per interface you doesn't need to configure the command native vlan, you only need the command switchport trunk encapsulation dot1q, switchport mode trunk, and it works, but the vlan allowed on this trunk is all from 1 to 4095, and the native is implicit vlan 1. If switch on both side are cdp enabled on trunk interface, and different natvie is specified on one of the switch you will see this error, %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered, and need to see the configuration and change tha native on one of the side.

avilt Sun, 12/11/2011 - 16:50

Thank You,

Long back allowing vlan1 on trunk port was mandatory however it's not required anymore. How is it achieved and what is vlan1 minimization?

Beetlejuice01 Mon, 12/12/2011 - 00:11

On trunk link, switchport trunk allowed vlan 2,3,5,10... or 10-15 if you would insert single vlan put a , between vlan if is a range from 10 to 15 for example put the -.

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Posted December 8, 2011 at 11:05 PM
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