Ah, so I was incorrect in assuming that mayhem and chaos might ensue if
there were a native VLAN mismatch. I thought that traffic from one VLAN
might be mixed with traffic from the other VLAN. But if I understand
you correctly, they would never actually begin trunking in the first
place, right? Hmm....
Then again, even if they weren't trunking, if the ports were active
then traffic would still be intermixed. I guess the moral of the story
is to make sure your native VLANs match!
John
>>> "Karen E Young" 7/23/01 1:49:00 PM >>>
Priscilla,
A native VLAN is the VLAN that a port functions under when its not
trunking.
When the switch comes online one of the things it does is perform any
negotiations for trunking. In order to negotiate the two ports need to
be
able to communicate at layer 2. If the ports at either end of the
proposed
trunk link belong to different native VLANs then they won't be able to
communicate to negotiate the trunking. Negotiations can fail for other
reasons though too, such as when trunking itself is misconfigured.
Anyway,
if negotiations fail or if trunking goes down for some reason, then
the
ports revert to their native VLANs. The default native VLAN of a Cisco
switch is VLAN 1. Other vendors have been known to use VLAN 100.
HTH,
Karen
*********** REPLY SEPARATOR ***********
On 7/23/2001 at 3:04 PM Priscilla Oppenheimer wrote:
>At 08:53 AM 7/23/01, Remmert Veen wrote:
>>Hi Sammi,
>>
>>Indeed, ISL is Cisco propietary, so should you consider other
vendor's
>>switches in your network, now or in the future, I'd recommend
802.1q.
Beware
>>however, dot1q has some drwabacks with regards to loops. Check out
>>http://www.cisco.com/univercd/cc/td/doc/product/lan/c2900xl/29_35wc/sc/swgvlans.htm#xtocid1196639
>>for the details.
>
>I'm trying to understand what that link is saying:
>
>"Make sure the native VLAN for an 802.1Q trunk is the same on both
ends of
>the trunk link. If the native VLAN on one end of the trunk is
different
>from the native VLAN on the other end, spanning-tree loops might
result."
>
>What's a native VLAN? Is that the one that sends STP, VTP, etc.? How
is it
>different from the management VLAN?
>
>If the native VLAN were set differently on the two ends of a trunk, I
guess
>STP traffic wouldn't flow correctly, so loops could result? Why
wouldn't
>this also be a problem for ISL?
>
>The link also says this:
>
>"Disabling STP on the native VLAN of an 802.1Q trunk without disabling
STP
>on every VLAN in the network can potentially cause STP loops. We
recommend
>that you leave STP enabled on the native VLAN of an 802.1Q trunk or
disable
>STP on every VLAN in the network. Make sure your network is loop-free
>before disabling STP."
>
>That one seems sort of obvious. Disabling STP on any trunk could
result in
>problems, I would think. What are they getting at?
>
>Thanks,
>
>Priscilla
>
>
>
>>If not (so your network is all Cisco) you might wanna consider ISL.
Since
it
>>is Cisco propietary, it's obviously fully supported by Cisco and has
some
>>minor benefits.
>>
>>Hth,
>>Remmert
>________________________
>
>Priscilla Oppenheimer
>http://www.priscilla.com
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=13422&t=13325
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