Network Loops: The Perils of Cabling Carelessly

Network Cable -

Today’s content is a little dry but if you actually take the time to read it, the day will likely come when you’ll be glad you did!


The Internet goes down at your home or (small business) office. You reset the router and the modem. Perhaps your Internet connectivity is briefly restored and perhaps not… but within seconds you’re back to not being able to get online. You call your ISP. They say they’re able to communicate with your modem and there is no general outage in the area. The problem must be on your end, they explain.


A “network loop” is a common problem in home and small business networks. Most small businesses don’t have the network equipment necessary to prevent network loops. Unless someone in your home is an IT pro who takes management of your home network very seriously, you don’t have that equipment in your home either. I don’t have it in my home. So, unless you’re going to invest in the equipment necessary to prevent network loops and spend hours learning how to program it, you’d better learn what a network loop is and how to fix it. Don’t worry… it’s super easy!


A network loop occurs when two switches are connected more than once or a switch is connected to itself. This doesn’t apply to ‘smart’ switches like those used in enterprise environments… we’re talking about small business and home environments here. When a network loop occurs, the network becomes flooded with data traffic to the point that it becomes non-functional.


Network loops occur fairly frequently in small business environments when a staff member (like a cleaning person) sees a network cable hanging loose out of a wall jack and decides it looks sloppy. So they plug the other end of the cable in to the other jack. Each of those wall jacks is connected to a port on a switch in the wiring closet. A network loop is created and, within seconds, nobody can check their email or surf the web.


At home, maybe little brother decided that the network would run even faster if he connected all the ports on your router to ports on the switch. Maybe the wife plugged the router in to itself because she saw a network cable hanging loose from it. Maybe your husband, for whatever reason, connected two switches together with a network cable even though both are already connected to a router.


All of these situations will create a network loop and stop your network from functioning. To stop the network loop and restore your network to working order, you must find the errant cable(s) and unplug it/them. At home, this should be pretty easy. At a business, you might have to do some hunting (or call your IT service provider if this sort of thing is covered by your service contract… it really should be!)


As you seek out the problem, remember these two rules. They’ll help you find the majority of loops.

(1) A thing must not be plugged in to itself with a network cable. (A sub-rule of this is that the wall should not be plugged in to itself).

(2) A thing should connect to another thing only once via a network cable. If two network cables run between two devices, it should be considered suspect. If you work at a place with on-site IT, this should really be their domain. You shouldn’t unplug network cables without asking unless you’re positive you know what you’re doing.


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