One Ethernet Cable connected only to Output ports

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olaf2000

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Feb 26, 2016
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I was wanting to know what would happen if you connected one ethernet cable to only the output ports of one router. Why? Someone says that is what caused a local network to completely fail.
 
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It greatly depends on the router. In general a stupid router you will get a massive loop of broadcast packets that will in effect take down the lan.

A smarter router run a protocol called spanning tree that detects these loops. I would normally have told you any consumer router would loop but I have found spanning tree on a couple and but there are absolutely no settings in the device and I could find nothing in the documentation but you can see the BPDU packets being sent so it has to support it.

I am still going to bet the vast majority of routers will get massive traffic loops.
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USAFRet

USAFRet

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Mar 16, 2013
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Much more backstory needed here.
Preferably a diagram of what you are trying to do.
 
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olaf2000

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Feb 26, 2016
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Sorry, I should provide a better explanation. One cable connected between two LAN ports of the same router.
Example one cable with one end connected to LAN1 and the other end to LAN2 of the Same Router.
 
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USAFRet

USAFRet

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What will happen? Nothing.
The router won't be magically imbued with extra powers, but it also will not explode.
 
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BuddhaSkoota

BuddhaSkoota

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Aug 16, 2014
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Two ports on the same router or switch looped together will absolutely cause problems and normally will cause a network to completely fail. I have personally seen this problem shut down a LAN.

https://en.wikipedia.org/wiki/Switching_loop
 
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bill001g

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Aug 9, 2012
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It greatly depends on the router. In general a stupid router you will get a massive loop of broadcast packets that will in effect take down the lan.

A smarter router run a protocol called spanning tree that detects these loops. I would normally have told you any consumer router would loop but I have found spanning tree on a couple and but there are absolutely no settings in the device and I could find nothing in the documentation but you can see the BPDU packets being sent so it has to support it.

I am still going to bet the vast majority of routers will get massive traffic loops.
 
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