Specifically allow Native VLAN on Trunk

[amit.bhagat]

Hi All,

I see an unusual behavior with Cisco Catalyst 6504 IOS 12.2(17r)SX7. The topology is very simple. This 6504 has trunk port to 2 devices at each end.

Device1-------(Trunk)------6504-------(Trunk)---------Device2.

All this switch does is allow VLAN tagged traffic between 2 devices. The issue is unless I specifically mention native VLAN 1 on these trunks, traffic does NOT pass through the switch. Also, if I try to tag Native VLAN, again, the traffic does not go through. I just want to understand if this is a normal behavior with Cisco 6504, or I am missing some VLAN concept.

I should mention that the VLANs that this switch passes through are not configured on the switch.

Any help would be much appreciated.

Thanks.

Amit.

[Reza Sharifi]

Hi Amit,

All you need on your 6500 is trunk ports to these 2 switches and allowing the vlans on these trunks.  Native vlan (vlan 1) by default is on trunk links and it is used for traffic that does not need to be tagged and also used for control traffic like VTP, VRRP, HSRP, etc..  So, you don't need to configure native vlan at all.

HTH

[Florin Barhala]

Can you post the trunk ports configuration together with show vlan brief

If you want the "normal behavior" of your trunk you should define these vlans on your 6500 switch. If not you have to use VLAN 1 as "a transport vlan" and configure it properly as you mentioned.