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4 Posts


October 4th, 2023 16:06

VLT spanning tree problem

Hi all,

Could you please assist me with the following problem?

i have the following GNS3 topology

i have configured VLT between Sw1 and SW2. I also configured a vlp port channel between the logical node SW1-SW2 and the IOSvL2.
When i do a continous ping from PC1 to PC3 and i shut port G0/1 on IOSvL2 ths vlt undertands that the link G0/1-e1/1/1(sw2) is down but the ping goes on.
If i bring G0/1 up thus restoring the link and i then shut the G0/0 down, the ping gets timed-out (sometimes a ping gets through). When i check the SPT i see that Po1 at SW2 is ALD and BLW in state.
cisco runs rstp and SW1 and SW2 also rstp
Any ideas? Could it be a bug of GNS3?
both dell switches are S4128F-ON (

1 Rookie


4 Posts

October 4th, 2023 19:43

one more thing. When both interfaces in the cisco are up then the po1 in both switches is concidered root and is in frd state.

If G0/0 goes down (sw1 is the primary switch in the VLTi)  the Po1 in both swi is concidered alt and is in blocking state.

Note that the cisco is the root switch



3.1K Posts

04-10-2023 08:48 PM

Hello Vkalob,


Could you try the latest Dell SmartFabric OS10 Version,, GNS3 Bundle


What do you get as output of these commands?

#show vlt brief

#show vlt role

#show vlt detail

#show spanning-tree brief

#show spanning-tree active

#show spanning-tree interface


DELL-Charles R

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Dell Technologies | Enterprise Support Services

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