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tuxtlequino
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When to enable any sort of stp?

Tue May 17, 2022 1:52 am

This is a simple question. In every example I have see of stp, I see that the configurations have routers in different branches connecting to each other. If in my configuration, I have something that looks like a simple tree in which the branch switches or routers never connect to each other other than through their root main router branch, is stp even necessary?
 
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StubArea51
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Re: When to enable any sort of stp?

Tue May 17, 2022 4:03 am

STP is really only needed on switch ports that have a potential for a loop or broadcast storm.

Typically, I turn STP off on the port when a router is connected and then leave it on when connected to a switch or bridge. End hosts and systems unlikely to loop can be assigned the edge role so that they don't affect the STP topology and go into forwarding immediately.

Also turn off STP when connecting to a network that is beyond your administrative control - a private L2 circuit, an ISP upstream, a customer network, etc.

There will always be exceptions, but this works well in most environments.
 
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Re: When to enable any sort of stp?

Tue May 17, 2022 5:53 pm

End hosts and systems unlikely to loop can be assigned the edge role so that they don't affect the STP topology and go into forwarding immediately.

That's fine when the network engineer is in full control of the network, but users are pesky creatures.

They plug $20 NetGear switches into single-drop wall jacks to get more ports, and then in their ignorance create a loop the dumb switch is incapable of pruning off locally, creating a loop through the wider LAN.

They take VoIP phones with pass-thru jacks for the PC and helpfully plug both ports in at once.

I get that it takes time for STP to converge, but that's why we have RTSP now. Let it do its job. A second or two per port to work out the new topology is cheap compared to human time chasing loops.
 
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StubArea51
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Re: When to enable any sort of stp?

Tue May 17, 2022 5:59 pm

End hosts and systems unlikely to loop can be assigned the edge role so that they don't affect the STP topology and go into forwarding immediately.

They plug $20 NetGear switches into single-drop wall jacks to get more ports, and then in their ignorance create a loop the dumb switch is incapable of pruning off locally, creating a loop through the wider LAN.

That's exactly why we have storm control and loop protect - no need to take the forwarding delay hit for all traffic when that problem is better solved elsewhere.

Loop protect is designed for exactly this scenario.

https://stubarea51.net/2016/11/16/mikro ... p-protect/

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tuxtlequino
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Re: When to enable any sort of stp?

Tue May 17, 2022 10:42 pm

That's exactly why we have storm control and loop protect - no need to take the forwarding delay hit for all traffic when that problem is better solved elsewhere.

Loop protect is designed for exactly this scenario.
That is great. I didn't know that. Although I have several routers/switches (11) in my facility, I do not need nor want "redundancy" at this point, but if that is the case, I need to remember the loop protect options.

In other words. No "redundancy," no need of stp. Because having no "redundancy" or alternate possible "routes" in between routers also means no possible "loops."

I was asking because it seemed as if stp was enabled in some of my routers without me actually choosing anything and I didn't want to go on disabling stp and later on causing some issues that were hard to trace back. Thank you all of you for answering this question.

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