STP and IP Phone

[Anonymous]

We are using IP phones on our network.  The IP phones have a switch built into them like most do so that the user can connect their computer into the IP phone.  we reciently had a user connect the IP phone to the network switch and then the phone switch port on the IP phone into the network switch as well.  I believe this would cause a Network Loop and broadcast stormes would kill out network.  The network was crushed when this phone was connected to the network switch with two cables.

I thought Spanning Tree Protocol would have prevented this.

I do have to put the ports into trunk mode as the Computers and IP phones are on different VLANs.  Is there something where spanning tree doesn't work on trunk ports?  If spanning tree was enable and configured correctly should it have prevented a network outage?

[Anonymous · Accepted solution]

@net_engineer - Thank you for your question. It would seem that spanning tree should have prevented the broadcast storm in this case. However, my experience has been that the data port and/or the network port of the IP phone do not forward BPDUs or, in other words, participate in spanning-tree. Therefore, the AOS switch would see the network port and data port of the IP phone as two individual edge devices.

Spanning-tree on AOS devices still operate even if the port is configured for trunk mode. However, to answer your question, if the IP phone and the AOS device had spanning-tree enabled on it, then, yes, it should have prevented a network outage. Spanning-tree is enabled on AOS devices by default. The following document has more information regarding spanning-tree in AOS that you may find helpful:

Spanning-Tree Protocol in AOS - https://supportforums.adtran.com/docs/DOC-1661

Please do not hesitate to reply to this post if you have any further questions.

Thanks,

Noor

[Anonymous]

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I went ahead and marked this post as "assumed answered."  Feel free to mark any correct or helpful answers from this post.  If you still need assistance with this issue I would be more than happy to help, just let me know in a reply.

Thanks,

Noor

[Anonymous]

@net_engineer:

I went ahead and flagged the "Correct Answer" on this post to make it more visible and help other members of the community find solutions more easily. If you don't feel like the answer I marked was correct, feel free to come back to this post and unmark it and select another in its place with the applicable buttons.  If you still need assistance, we would be more than happy to continue working with you on this - just let us know in a reply.

Thanks,

Levi