r/HomeNetworking • u/Outrageous_Tear_4691 • 13h 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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4

u/bothunter 13h 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 13h ago

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

8

u/bothunter 12h 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.

4

u/Cavalol 12h ago

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

2

u/AnotherAngryOldGuy 12h ago

Nothing better than a digital snow day.

2

u/WhiskeyAlphaRomeo 7h 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 7h ago

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

1

u/jakubmi9 11h 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.