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New Member

Remove VLAN 1 From Trunk Links

In Catalyst 6509, IOS 12.1:

Shutting Interface VLAN 1 down should not create any problems since the VLAN 1 itself will still be active. The question is that the latest IOS version allows you to remove VLAN 1 from you trunk ports which is fine as long as the Data and the Management VLAN is not 1. I was reading Cisco LAN Switching Book, and found out that most of the control traffic such as VTP, DISL/DTP (used for trunk negotiation) , CDP, and PAGP always use VLAN 1. Won't it create a major problem if VLAN 1 is removed from the trunk links. When is it possible to remove VLAN 1 from all trunk links.

Thanks

  • Other Network Infrastructure Subjects
4 REPLIES

Re: Remove VLAN 1 From Trunk Links

From Cisco:

VTP pruning cannot be applied to VLANs that need to exist everywhere and to be allowed on all switches in the campus (to be able to carry VTP, CDP traffic, and other control traffic). There is a way, however, to limit the extent of VLAN 1. This is a feature called VLAN 1 disable on trunk, and it is available on Catalyst 4000, 5000, and 6000 family switches since Cisco IOS release 5.4(x). This allows you to prune VLAN 1 from a trunk as you would do for any other VLAN, but this pruning will not include all of the control protocol traffic that will still be allowed on the trunk (DTP, PagP, CDP, VTP, and so on). However, you will block all user traffic on that trunk. Using this feature, you can completely avoid the VLAN spanning the entire campus, and as such, STP loops will be limited in extent, even in VLAN 1. You can configure VLAN 1 to be disabled as you would configure other VLANs to be cleared from the trunk by issuing the following commands:

switch> (enable) set trunk 2/1 Des

Port(s) 2/1 trunk mode set to desirable.

switch> (enable) clear trunk 2/1 1

Removing Vlan(s) 1 from allowed list.

Port 2/1 allowed vlans modified to 2-1005.

Hope it helps.

Steve

New Member

Re: Remove VLAN 1 From Trunk Links

Thanks Steve, This really cleared up lot of the issues for me. According to your reply, it means that if i clear VLAN1 from my all trunk links as you are recommending that everybody should do then it only disable VLAN for user traffic, but still enable for the control traffic. My swich has an integrated IOS, so I will just remove vlan1 from my all trunk links.

Should it matter what LAN Design one has. For Example, in my design I have two 6509 backbone switches with about 10 VLANS. Each Floor has it own Switch and VLAN. I am restricting my trunk links to each switch only to take the VLANS assigned to each floor. I will go head and also remove VLAN1 from all trunk links as well since it will still carry controll traffic.

Example,

int gigabit ethernet 2/1

switchport trunk encapsulation ISL

switchport mode trunk

switchport allowed vlan remove 1

Thanks again for your thorough reply.

Re: Remove VLAN 1 From Trunk Links

Yes, user data filtered but control traffic (DTP, PagP, CDP, VTP, and so on) allowed. Generally though, users/servers shouldn't be placed on vlan 1 anyway.

It shouldn't work with IOS switches though, only CatOS 5.4(x) or greater. You can set the trunk port to prune (switchport trunk pruning vlan ...) vlan 1, but not to remove/clear (switchport trunk allowed vlan...) vlan 1. You cannot remove any of the default VLANs (vlan 1 is default for ethernet) from a trunk on IOS trunks.

Prune the trunk links, thats the best you can do in your case - link on pruning: http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_guide_chapter09186a008007f695.html#10027

Hope it helps.

Steve

New Member

Re: Remove VLAN 1 From Trunk Links

VLAN minimization is available i IOS for the 6500 from 12.1(11b)E.

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