What does Router DHCP mean? The night I accidentally turned it off, the whole house went off the internet, and I figured out the address pool and the lease

night I cleared the router's background and found the switch "DHCP Server." The name sounded familiar—probably some unusable feature, so I accidentally turned it off. Ten minutes later, the whole family exploded: WiFi icons were all full, none of the web pages could be opened, my wife's phone, my computer, and the TV box in the living room all showed "no network connection."

later I realized that the one who shut down was the main butler that sends IP addresses to devices at home. This article will clearly explain what DHCP actually is, what terms like address pool and lease contracts mean, and when it should really be turned off.

What does

DHCP do: It issues the house numbers for all the devices in the house

every device needs an IP address to access the internet, which is equivalent to the home address number. When your phone connects to WiFi, you never need to enter your own IP address. Who gave you that number? It's the DHCP module inside the router—short for Dynamic Host Configuration Protocol, a name that sounds intimidating, and its job is to automatically send a door number.

process, to put it bluntly, in four sentences: the device connects to WiFi and shouts, "Has anyone sent the number?" The router replies, "I have 192.168.31.101, do you want it?"; The device says, "This is it." The router was decided: "Take it, I'll rent it to you for a while." A round trip takes two or three seconds, and you can't even sense it.

what happens after I turn it off? The device was connected to WiFi as usual—connecting to WiFi and getting a house number are two different things—but after calling for a long time, no one answered. Both Windows and Android have a backup logic: if you can't get the address, you create a number starting with 169.254. This range is reserved for "ownerless" devices, which can't access the internet and are just placeholders.

so when you see a 169.254 mark, there's a 90% chance something wrong with DHCP: either it's shut down, the pool is full, or some other machine is causing trouble online. I previously wrote about WiFi bars but can't get online I explained the troubleshooting approach for this number range, so I won't repeat it here. The most frustrating part is, once DHCP is turned off, you can't even access the router's backend—you need an IP to access the backend first. My solution that night: plug in the computer and network cable, manually set the IP to 192.168.31.88, set the gateway to 192.168.31.1, and the mask to 255.255.255.0, then squeezed into the background and turned on the switch. If you slip up your hand too, follow this formula to get the medicine.

address pool: routers only send

routers don't send numbers casually; there's an 'address pool' in the background. Home machines typically send numbers from 192.168.31.100 to 199, a total of 100 numbers. If you see that all the IPs of your home devices are crammed into over 100 in the device list, that's the reason.

more than enough for a hundred households. I counted a while ago at my house—there are 49 phones, computers, cameras, vacuum cleaners, and speakers, which takes up half the space. my post about smart homes I made a list: the ones that really occupy the number are those connected directly via WiFi, while the Zigbee bulbs and sockets go through the gateway and are resold without taking up a spot.

pool: Go to the backend and look for 'LAN Settings' or simply call it 'DHCP Settings.' Different brands use different names. In Xiaomi's commonly used LAN settings, TP and Mercury are mostly hidden under the network parameters in advanced settings. There are only two legitimate reasons for changing the banner: first, to make room for manually fixed IP devices (more details below); second, there really are hundreds of devices at home—in this case, I advise you to clear out the zombie devices first. I wrote about cleaning up 62 devices on an old router, just follow .

the pool is full and the symptoms are exactly the same as turning off DHCP: a new device connected to WiFi still gets 169.254. So when checking your equipment, don't forget to check if the pool size matches your home equipment.

lease will be cut off when it expires: No, it quietly renews halfway through

backend device list often has a "Remaining Lease Period" column, which makes many people anxious: "The lease is up, will my device disconnect?"

don't panic. The lease contract is the usage period of the number, which varies by brand by default—two hours for short, one day for longer. When half the time passes before the expiration date, the device will quietly renew the router, and the device in use will not notice it at all. The time you can truly sense it was when the device slept for several days without reconnecting—just reconnect to WiFi, which is the same as reconnecting when you disconnect from the internet.

lease is truly worth worrying about. One is zombie slot taking: the device has retired from the network and the account hasn't been returned, with a list full of "offline but occupying" records. Normally, this doesn't affect the situation, but when the pool gets stressed, it's manually deleted. Another issue is the phone's random MAC: phones with private addresses switch to different scenarios, routers act like new devices and new accounts, and the pool is slowly eaten—the unrecognizable manufacturer names in the device list mostly come from this method.

rules for manually filling static IPs: if you want to fill in, do so outside the pool

devices like printers, NAS, and cameras are suitable for fixed IPs; otherwise, a single restart changes the address, and port forwarding and sharing paths all have to be changed. I previously wrote about using static binding in the backend for , which is the first choice: it's like whitelisting DHCP, the device still automatically gets the number, but it always uses the same number.

some people try to save effort by directly filling in static IPs directly on their devices, which has a classic trap: they just add it to the pool. For example, if a printer manually enters 192.168.31.105 and falls into the 100 to 199 range, one day DHCP sends 105 to a newly connected phone, and the two devices have a different number. The symptoms fluctuate: pinging works but files can't be transferred, which is very confusing.

rules are simple: the handwritten address is outside the pool. If the pool is 100 to 199, just enter 192.168.31.50, or 201 or later. Enter the router address for the gateway, enter the router for DNS, and 223.5.5.5 for each router, ensuring both are active.

three situations, if you really want to turn off DHCP, don't touch it at all other times

DHCP just keep it open by default. But when the home network gets messed up to a certain stage, there are really three situations where you need to turn it off. The common logic is simple: there can only be one operator in a network; if you add one, things get messy.

the first method: the old router is replaced with an AP for use as a wireless switch. The DHCP for secondary routers must be turned off, and the numbers are uniformly issued by the main router. the old router is changed to AP, this is one of the four steps in the article, and if you miss it, all the device addresses in the house jump randomly.

second method: Hanging a bypass route. The main router sends signals as usual, while the bypass router turns off DHCP and only handles traffic. the car I wrote about in the about the bypass router was both sending signals, and the network fluctuated all night.

third method: connect the router from below the optical modem or main router. Again, only one message can be left, the article about connecting two routers with optical modem is the most detailed. The typical symptom of dual DHCP is "half the devices can access the internet, the other can't"—the devices randomly pick numbers from each of the two, each pointing to the gateway, which sounds mysterious but reveals the truth at a glance.

to determine who is currently sending the number at home, a single command matter: enter ipconfig on the computer to check the default gateway, the gateway is 192.168.31.1, and the number is that Xiaomi; if the gateway is 192.168.1.1, then most likely the optical modem is sending it.

don't overlook one major premise: whoever dials is the machine that sends the number

changing the pool and turning off the switch all come with one prerequisite—your router is really the one that issues the numbers. When the modem is running in routing mode, it's actually dialing and sending numbers, while your router is just acting as an AP. At this point, trying to change the address pool in the router's backend can't send out a single number—it's just a wasted effort.

can't tell who dialed the number. Just look at the three-step method I wrote about the optical modem and router being 192.168.1.1 . If you really want to change the banner, you have to go to the optical modem backend. in the article about changing the LAN port IP, I once fell into the trap of "the IP change didn't keep up" in the of the optical modem. Just go back and check accordingly.

Finally, here's the order of inspection. When WiFi is fully blocked and the device IP is 169.254, follow this chart:

only two commands: on the computer, go to ipconfig /release, then ipconfig /renew, and reget the number. If you forget your phone, reconnect to the network. Ninety percent of cases are revealed by the third step.