Question regarding STP and root

[tommygunnah]

*Please refer to attached picture*

After running in to some routing issues I discovered recently that there may also be issues within the STP.

Currently we have everything on vlan 1 with a network of 10.18.24.0 255.255.248.0.

Instead of the root bridge being our 3850 (WHich was replaced some time ago) The root for vlan 1 is actually on a 4507 that belongs to a partner that also sits inline with our network. I dont have access to that 4507 but was wondering if I changed the root back to 3850 if I would cause any issues on the side of the 4507?

[guillermonrvz83]

Check the bridge priority on your 3850. 

[tommygunnah]

Bridge priority is set to default 32769

[chrihussey]

Your topology does not indicate that there are any loops and that it is more of a hub and spoke configuration. My impression is that setting the 3850 back to the root bridge (as it once was) should have little to no impact.

That being said, it would be advisable do it in the off hours as a precaution just in case something unexpected occurs.

If you have any other thoughts or concerns just say so.

Hope this helps.

[tommygunnah]

So if the vendors 4507 is set to be the root bridge for our vlan 1 traffic wouldn't it be best practice to bring that back to the core? Sorry Im still new to all this.

[chrihussey]

Yes it would. Especially if your 3850 is the core.

Post the output of "show spanning-tree root" of the 3850.

[tommygunnah]

Root Hello Max Fwd
Vlan Root ID Cost Time Age Dly Root Port
---------------- -------------------- --------- ----- --- --- ------------
VLAN0001 6089 0023.04ee.be03 20209 2 20 15 Gi1/0/48
VLAN0130 32898 706e.6dc5.e880 0 2 20 15

[chrihussey]

So assuming G1/0/48 is the 3850 port that faces the 3560 which then connects to the 4507, it looks as if the 4507 has a configuration to make it the spanning tree root. However, if the topology is what it is and you share/control VLAN 1, making the 3850 root would be the way to go. (spanning-tree vlan 1 priority 0).

As I said earlier, it should be no big deal to implement. I've done it many times with no issues. But not knowing all the detailsof your network, just do it in the off hours to be safe.

Hope this helps.

[tommygunnah]

Chris,

Thank you very much for the advice.

If things were to go awry, would I just change the priority back to default on the 3850?

[chrihussey]

Yes, that would be the way to go.

Honestly, it should be cut and dry. If something goes wrong there is something else going on.

If you do run into any issues, just try and define what the problem is, get what you info can from the switches and post it.