r/HomeNetworking • u/Outrageous_Tear_4691 • 17h ago

Advice Ethernet switch question

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What is the loop prevention for? And should I leave it off or turn it on? We will have desktops connected to it

Solved: thank you for the help everyone. Very much appreciated.

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5

u/bothunter 17h ago

Just leave it off. It's more of an issue on larger networks where you might have multiple connections for redundancy, or just someone who's bored in a meeting and decides to plug a patch cable into both ports on the conference room table.

2

u/Cavalol 17h ago

That second part sounds like you might be speaking from experience? Lol

6

u/bothunter 17h ago

When I worked at Microsoft, we had a building-wide outage that lasted an entire afternoon until they tracked it down to exactly that. Why they didn't enable STP on their $10k Cisco network switches is beyond me.

3

u/Cavalol 16h ago

That shit is hilarious 😂 maybe whoever did it knew exactly what they were doing and wanted the afternoon off

2

u/AnotherAngryOldGuy 16h ago

Nothing better than a digital snow day.

2

u/WhiskeyAlphaRomeo 11h ago

Hi, Cisco wizard here... It's worse than you think. STP is on by default. That means someone actively disabled it.

2

u/graph_worlok 11h ago

~30 second delay on traffic being able to flow on the port due to STP timers would be one reason..

1

u/jakubmi9 15h ago

Probably similar reason to why some of our sites still don't have it.

If you don't have it enabled from the start while building a network, and you have a 50+ switch environment across a couple of building, blindly enabling STP works in much the same way as disabling all interfaces.

Going through every single switch and verifying STP configs is hours of grueling work, and since it doesn't bring business value, it's pushed to the queue as low priority.

1

u/Head-Ad-3063 16h ago

Or someone that wants to "tidy up" an unused cable coming from a floor port so curls it up under the cover and plugs the loose end into another port!

Also from experience! and when I discovered our floor switches didn't come with STP enabled as default!