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When the internet appears to have crashed, the service provider invariably gives this advice as a first line remedy: unplug the router from the wall socket, then wait 5 minutes, then plug it back in. Many times this remedy works.

Question: Why does the router care if it's been unplugged from the wall versus simply turning it off? And more interestingly, what happens during the 5 minute interval that the router is unplugged; if it has no electricity, is it not merely in a deadened state?

Gayot Fow
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    With how often this advice is dispensed, I'm surprised router manufacturers haven't put a giant "Reset" button of some kind front-and-center on their routers. – JYelton Jul 28 '14 at 20:54
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    @JYelton: Some do. – keshlam Jul 28 '14 at 21:48
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    The reset button, at least on my router (D-Link), puts the router back in its initial state when taken out of the box. If you use the reset button, you will have to re-program the router. – Barry Jul 28 '14 at 23:24
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    Amongst other things, it has to do with the central end router (DSLAM) that requires a timeout to release the connection. Only then it will set up a new and fresh connection, forgetting previous state. – jippie Jul 29 '14 at 16:44
  • Would installing a switch work, or is it necessary to disconnect both neutral AND live cables? –  May 11 '15 at 21:54

6 Answers6

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What you are waiting can be two things. One is for the ISP to "release" your dynamic IP address, and after 'x' minutes, when powered back on, the MRC (Modem/router combo) will be re-assigned an IP address to its MAC address.

The other reason is to allow a internal capacitor to discharge completely to allow the volatile memory that contains the cache to be cleared. Clearing this cache can often "resolve" the issue.

Enemy Of the State Machine
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  • Agreed. D The "on/off" switch is often NOT a "mains-disconnect" switch. In the "off" state, there is still power to the memory circuits. A good way to check this is a "Kill-a-Watt" type meter. If you "power-off" any device and there is power being used, it is not using a true "mains-disconnect" type switch. – Enemy Of the State Machine Jul 28 '14 at 20:38
  • Got it. Please re-edit my tags to assure they are the correct tags with the appropriate electrical buzzwords. Many thanks. – Gayot Fow Jul 28 '14 at 20:41
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    A DHCP release won't happen in five minutes, and a capacitor discharge will happen in five seconds. This is likely just a myth that keeps circulating in tech support because it says so on the checklist they have to go through. – ntoskrnl Jul 29 '14 at 10:43
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    @ntoskrnl A DHCP release will not happen in five minutes (baring pathological settings). However it is enough to insure that the DHCP discovery process is repeated. - And hence that the client will re-receive DHCP information. (Although here too 5 sek is probably enough). A difference could be that the server would not detect the client as having gone offline if it's just offline in 5 sek. – Taemyr Jul 29 '14 at 13:10
  • @ntoskrnl Could it be that the five minutes is sufficient to expire ARP cache entries on devices communicating with the router? Is there some advantage to having ARP caches expired before the router is powered on again? – kasperd Jul 30 '14 at 08:14
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Some devices don't fully power down when you turn them off, they simply go into a low power standby state. By unplugging it you make sure that it shuts down complete and has to go through an entire reboot sequence. The 5 minutes are a combination of allowing the internal power supply to completely discharge and for the link to your ISP's equipment to drop. That time allows for the remote equipment to realize that the signal on your end has actually dropped rather than it being a temporary glitch. That clears out any held state and forces a full renegotiation when your router comes back online.

Chris Ryding
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If you have a 'hard' on/off switch this should have the same effect as pulling the plug. But a lot of devices nowadays have a 'software managed' switch, which is of course useless when you want to force a hard reset on the software.

The 5 minutes is to make sure that the device has really lost its power. A power supply unit, especially a switched mode one, can have a decent amount of stored energy. It might not be enough to power the device in a proper way, but it might be enough (for some time) to keep the device in some half-powered state, in which re-powering it would not mean a full reset.

So in the end both instructions are to make double sure that the device gets a hard reset.

Wouter van Ooijen
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    I had a printer technical support line suggest I unplug the printer for 24 hours, then try again. I figure the next day was that support person's day off... – markrages Jul 28 '14 at 21:14
  • @markrages, must have be some *huge* capacitors in that printer. – sherrellbc Jul 29 '14 at 00:02
  • @markrages HP I'm guessing. I got the same "advice" from them frequently for the early model Laserjet 4 series. – Tonny Jul 29 '14 at 12:46
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I believe the true answer here is not only a technical one, but also the simple fact that people are idiots. Especially those who end up calling technical support for router issues. That's a sad fact but unfortunately it's the case. Support agents there get the kind of calls where people ask why their device does not work and end up being told that they need to connect it to a power plug.

So, by telling people to simply unplug the router you avoid any kind of idiocy such as pulling the network cable instead, using the reset button, etc.

Additionally, many routers don't even have a power switch (not even one that just sends them into a hibernate-like state). So for the average user "unplug it from the power socket" is easier to understand than "turn it off" which would probably be followed up with a "how???? there's no off switch!!!!".

ThiefMaster
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  • By definition, 50% of people have an IQ less than 100. But you are right, most people who call tech support are probably entirely ignorant about network hardware. – ntoskrnl Jul 29 '14 at 10:46
  • I worked in tech support for ISP's for a number of years and never got a call for a device that wasn't connected. I did get one caller who managed to wedge a CD into a 5.25" drive... it didn't work. – James Snell Jul 29 '14 at 19:54
  • This. Technical staff can save a lot of time by giving more generic answers that are very likely to fix most problems than addressing the problem specifically. i.e. "Have you tried rebooting your computer?" instead of "Can you open task manager and check your memory usage?" – korylprince Jul 30 '14 at 02:11
  • I vaguely remember reading a story about a tech support guy trying to fix some monitor issue over the phone. He was certain that the monitor cable wasn't connected properly despite the user claiming he had already unplugged/replugged it and made sure it was seated correctly. In the end, the tech support guy told him that the cables might be 'reversed' and told the user to switch the ends around which worked. Most likely, the user was lazy and told tech support he had reseated the cable when he hadn't. I suspect the unplug-from-wall thing may be similar. – tangrs Jul 30 '14 at 13:08
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I suspect that the "unplug it for 5 minutes" directive is given for a number of reasons.

  1. Many routers and similar devices do not have a power switch & if they do, as was stated earlier, it may not completely remove power from the device. Since tech support - especially for an ISP - can't be sure of the details of every customer's device, therefore the advice is to unplug it.

  2. As for the 5 minute dead time interval, it is likely several things. First, the device needs to be powered down long enough for internal circuits to drain and thereby clear cache, etc. Second, as stated earlier, it is likely that seconds rather than minutes are what is required. But... By using the 5 minute advice, tech support can have some degree of confidence that if the customer waits only a fraction of the interval it will be long enough to do the job.

  3. I won't go so far as to say that users are idiots, but I have witnessed people (who can otherwise function and operate in their daily lives) go completely blank when directed to plug/unplug a power cord for computer equipment. It is like they know what the power cord for their fridge/toaster/lamp looks like, but when the word computer is added it becomes shrouded in mystery.

user3877056
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Years ago I worked in ISP support for a range of national and international providers. Answering this question is as much about the call centre environment (and usually outsourcing) than the technical reasons.

Technical Reasons

The router your ISP gives you (often for free) is selected based on cost not reliability...

  • The memory isn't error checking/correcting so glitches will happen occasionally.
  • The cheapest manufacturer's firmware is probably written by the cheapest staff, it probably doesn't clean up after itself and runs itself out of resources.
  • The DSLAM (or equivalent) is often crappy for the same reason as the free router and a little time of inactivity gives it plenty of time to know that the connection is actually gone rather than just a dropout. That makes sure the ATM layer, PPPoE/PPPoA, DHCP and everything else that may be needed depending on the provider's configuration is renegotiated.

All those are quickly fixed by a power cycle with a short delay. Technically that delay would be in the order of a few seconds but there's more to it than that...

Caller Reasons

Not everyone who calls up is stupid...

  • Some call to ask if it is them or the ISP at fault as much as anything else and to register their displeasure.
  • Some lack the confidence to know if it's ok to power-cycle the router - that is not stupidity. I lack the confidence to go even tandem skydiving and that's just walking/jumping through a door.
  • Some forget the router is there. It sits in a corner out of sight silently flashing away and usually 'just works'.
  • Some can't judge the 30 seconds that is more than ample to discharge the capacitors, so it's best to over estimate how long it needs than underestimate. 30 Seconds of silence in a phone conversation feels like forever.

Commercial Reasons

Outsourced call centres for this kind of work are typically paid per call while the staff are paid a pittance and treated like scum. Suggesting a reboot with a wait is profitable because it is:-

  • Most likely to fix the problem (it really is!)
  • Easy for "techs" to explain to customers.
  • Gets a caller off the line quickly (allowing "techs" to take more calls per hour since they don't have to wait.)
  • If they have to call back into a queue the call centre may get termination rates.
  • Many contracts have a stipulation that if the caller calls back within a certain time that it counts as a continuation the same call. This is also a good reason why you might find 5 minutes as a common value.

TL;DR

The power-cycle is as much about giving the network equipment a chance to reset as the router itself (customer/premises equipment) but five minutes is a business driven value.

"techs" is a term that needs inverted commas as you could train pretty much anyone who is polite and speaks the language to do the job from never having turned a computer on in 5 days easily. They are rarely technical in any way and politeness (like ability to speak the language) is frequently considered optional to save costs.

James Snell
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