[c-nsp] VTP and Vlan 1

Paul Cosgrove paul.cosgrove at heanet.ie
Mon Aug 25 14:50:28 EDT 2008

Hi Michel,

You may have been right the first time there.  I think VTP does indeed
use the native vlan, not necessarily vlan 1.  DTP is also sent on the
native vlan, untagged and tagged in its case.


Michel Grossenbacher wrote:
> A little correction on my answer, VTP does not use the Native VLAN :-)
> Here is what I found regarding the use of VTP and VLAN1:
> The Case of VLAN 1
> You cannot apply VTP pruning to VLANs that need to exist everywhere and that
> need to be allowed on all switches in the campus, in order to be able to
> carry VTP, Cisco Discovery Protocol [CDP] traffic, and other control
> traffic. However, there is a way to limit the extent of VLAN 1. The feature
> is called VLAN 1 disable on trunk. The feature is available on Catalyst
> 4500/4000, 5500/5000, and 6500/6000 series switches in CatOS software
> release 5.4(x) and later. The feature allows you to prune VLAN 1 from a
> trunk, as you do for any other VLAN. This pruning does not include all the
> control protocol traffic that is still allowed on the trunk (DTP, PAgP, CDP,
> VTP, and others). However, the pruning does block all user traffic on that
> trunk. With this feature, you can keep the VLAN from spanning the entire
> campus. STP loops are limited in extent, even in VLAN 1. Configure VLAN 1 to
> be disabled, as you would configure other VLANs to be cleared from the
> trunk:
> UDLD uses native VLAN in order to talk to the neighbor. So, in a trunk port,
> the native VLAN must not be pruned in order for UDLD to work properly.
> http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080890613.shtml
> Sorry for the confusion.
> best regards
> Michel
> On 25/08/2008, Michel Grossenbacher <pashtuk at gmail.com> wrote:
>> Hi Mike
>> Actually VLAN 1 is not pruning-eligible so you can not prune VLAN 1 from a
>> trunk. However you can remove it from the trunk.
>> If you remove it from the trunk and change the native VLAN for the trunk,
>> VTP will then use the new native VLAN for updates.
>> best regards
>> Michel
>>  On 25/08/2008, Mike Louis <MLouis at nwnit.com> wrote:
>>> List,
>>> I just read in a practice test for an upcoming cert that Vlan 1 is used to
>>> carry VTP advertisements. However, it is possible to prune vlan 1 from trunk
>>> links. Will VTP continue to function without Vlan 1 being enabled on the
>>> link? Has this changed in more recent IOS releases?
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