Simple question regarding Trunking/VLANs!

[mdnowicky]

Hi all,

This one is simple.

When you create a trunk port, do you need to specify VLANs using the "switchport trunk allowed vlan add" command?

If there are no allowed vlans specified, will that trunk then pass ALL vlan traffic or none at all?

[Jan Rolny]

Hi Matt,

trunk will pass all the traffic if you will not specify vlan number.

When you issue this command, trunk should limit traffic for vlan 15 to 20

switchport trunk allowed vlan 15-20

Simply if you do not issue this command so ALL VLANs are allowed by default.

or

If you issue this command switchport trunk allowed vlan all so it will have same efect as default.

Best regards,

Jan

[glen.grant]

    If you don't restrict the trunk then whatever is on the other end  will see all broadcast traffic for all vlans defined on the switch.

[JohnTylerPearce]

By default, when you create a trunk, all vlans will be allowed to traverse the trunk. You can also specify which vlans to traverse the trunk to help limit broadcasts.
z
'Switch mode trunk' allows all vlans by default.

'switch trunk allowed vlan add vlan-id' to specify specific vlans to traverse the trunk.


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