Spanning Tree problem / physical connection between two vlans

Unanswered Question
Jan 28th, 2008
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status:we have a switch with a vlan 10 and a vlan 900. VL 10 is our stand network and vlan 900 is a layer 2 vlan for a DSL connection.

How can i detect / check when there is a physical interconnetion betwein those two ports. And perhaps shutdown the VL 900 port?



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nordick26 Mon, 01/28/2008 - 02:48
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Hi Udo,

What do you mean by "physical interconnection"?

If you have two VLANs on one switch, they won't be able to interconnect users between each VLAN unless you have configured interface vlan 900 on you swich (and interface vlan 10 as well). This will act as a L3 interface and thus switch will be able to interconnect the users from both VLANs. You can then shutdown VLAN 900 L3 port by

interface vlan 900


Or if you have an uplink router connected to this switch and you are trunking both VLANs (10 and 900) to this router, you can connect users in these two VLANs.

You can chcec correct trunking on your switch by:

show interface XY trunk

Without L3 interfaces, users in VLAN10 and VLAN900 are separeted.



[pls rate any helpful posts]

winkelu Mon, 01/28/2008 - 02:53
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Hello Ivan,

the problem are the users

VL 900 and VL 10 are normaly on separted ports on the vlan. but sometime the uers interconnect those two ports by mistake with a cable



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