Dell 6224 STP blocking uplink port to Internet

[Shay2501]

I have a Dell 6224 switch with 5 Vlans defined, one for Lan, one for a subcompany LAN, 2 for DMZ - one for each LAN, and then one for straight to the Internet.

When I uplink the Internet port (Vlan 3), its STP status is Discarding and Role is Alternate. So it is dedicating this as an alternate root indicating a loop.

The actual root is the uplink to the LAN, the default VLAN 1.

So, if there was a loop, I should be able to unplug the uplink to the LAN and it would make the Internet uplink the root and the path to this switch would be restored, but it isn't. I can turn of STP on the Internet uplink port and that works, but I think there is a problem that needs to be addressed, not ignored.

I have verified there isn't a loop, the Internet uplink goes to the switch that has the uplink to the router out to the Internet.

I am out of ideas and need some additional suggestions as to what could be causing the problem. Your help is greatly appreciated.

 

[cajuntank]

What device are you plugging the switch into to get to the Internet?

 

[Shay2501]

I am plugging the Dell 6224 that is having the problem into a Dell 3448 switch. This switch has 2 other Linksys switches uplinking to it as well as our Cisco router out to the Internet.

 

[cajuntank]

Have you checked for a loop on one of the other switches?

 

[Shay2501]

Yes I have checked for loops on the other switches.

I think the problem may relate to Dell switch not having a separate STP root for each VLAN. The Dell 3448 has 2 vlans, one for the Internet and one for the office LAN. If STP has only one root per switch, it may think this is a loop?

I can't find any documentation on Dell's STP topology for VLANS.

 

[Shay2501]

I found MSTP and have set my switch to use that. I went and configured Instances for each VLAN, but the port is still in a discarding state and alternate role.

So, there must be some configuration that I am missing to make this work.