Skip to content

Troubleshooting

The one-sentence version: Most home-network failures are one of five stories — no address, wrong network, name doesn't resolve, blocked path, or the router changed underneath you. Match your symptom, work the steps in order, and check which of the router's four jobs is at fault before changing anything.

How to use this chapter

Each symptom lists the most likely cause first. Do the checks in order; stop when it's fixed. Resist changing three settings at once — if it starts working you won't know which change did it, and you'll do it again next time.

A useful first command on any misbehaving machine (typical output — your addresses will differ):

# Linux / Mac
ip addr show 2>/dev/null | grep "inet " || ifconfig | grep "inet "

inet 192.168.1.42/24 brd 192.168.1.255 scope global dynamic

No inet line on the active interface = the device has no address at all → start with \"new device gets no IP.\" Windows equivalent: ipconfig and look for \"IPv4 Address.\"

Can't reach the printer

  1. Is the printer awake and on the network? Printers sleep hard. Wake it, wait 30 seconds, try again.
  2. Did its address change? Print the network config page from the printer's panel and compare with the address your computer is trying. If it moved → give it a DHCP reservation so it stops.
  3. Try the address, not the name. If http://192.168.1.25 (printer's web page) loads but printer.local doesn't, it's a name problem (Names on Your LAN), not a printer problem.
  4. Guest network? If your computer is on the guest SSID, it can't see the printer — by design. Move to the main network.

Works on Wi-Fi but not ethernet (or vice versa)

The device is on two different networks without you realizing it — e.g., Wi-Fi joined the ISP gateway's network while the cable goes to your router, or vice versa. Compare the addresses: Wi-Fi 192.168.0.x vs ethernet 192.168.1.x means two routers are both active (see Double NAT and Gotchas). Fix: one router does routing; the other goes to bridge mode, and every cable and SSID hangs off the same one.

New device gets no IP

  1. DHCP pool exhausted? Check the router's DHCP client list. A pool of 100 addresses with 100 clients means the new device gets nothing. (Rare in homes — but a stuck pool full of long-dead leases happens.)
  2. DHCP server off? If you run DHCP from a Pi or second box and it's down, nothing new gets an address. Devices with old leases keep working — the classic \"everything old works, nothing new connects.\"
  3. Wrong network cable / VLAN port. A device plugged into a port assigned to an empty VLAN gets silence. Move it to a known-good port.
  4. As a test only: assign a temporary static IP in the right range. If that works, DHCP specifically is the fault — don't leave the static in place; fix DHCP.

Slow Wi-Fi in one room

  1. Confirm it's Wi-Fi, not the internet: speed test next to the router vs in the bad room. Collapses with distance → it's the path (see Wi-Fi That Matters).
  2. Check the band: the device may be clinging to 2.4 GHz. Forget the network and rejoin near the router, or split SSIDs so you can choose 5 GHz manually.
  3. Look for the new interference: the dead room started when the baby monitor / new TV / mirror went in? 2.4 GHz shares airspace with a lot of household gadgets.
  4. One room, always, everything tried: that's construction (brick, concrete, plaster-and-lath). The fix is a wired access point on the near side of the wall, not a stronger router.

"I replaced the router and everything broke"

The new router brought a new LAN subnet, new Wi-Fi name, no reservations, and no port forwards. Work the migration list:

  1. Set the new router's LAN to the old subnet (e.g. 192.168.1.0/24) so every static IP and bookmark still points somewhere real.
  2. Reuse the old SSID and password so devices rejoin silently.
  3. Re-create DHCP reservations for servers/printers.
  4. Re-create port forwards (or better, revisit whether you still need them — Port Forwarding).
  5. If the old router was in bridge-behind-ISP-box harmony, put the new one there too — check for double NAT.

Can't reach a home service from outside

  1. Test from outside properly: phone on cellular, Wi-Fi off. Testing from inside your own LAN can succeed via the internal address and tell you nothing about the outside path.
  2. Is the service listening where you think? From inside, curl http://<server-ip>:<port> should answer. If not, the service itself is down — no router setting fixes that.
  3. Port forward pointing at the right machine? The server's address must match its current reservation. A stale rule forwards the internet to whatever took the old address.
  4. CGNAT? If the router's WAN is in 100.64.0.0/10, inbound IPv4 cannot work — stop debugging the rule and read Double NAT and Gotchas.
  5. ISP blocking? Some ISPs block inbound port 80/443 (and sometimes 25) on residential plans. The rule is fine; the ISP drops it before it arrives. A non-standard external port, or a tunnel/mesh instead, sidesteps this.

A name resolves to the wrong address

  1. Flush the cache: the old answer is cached somewhere — device, browser, or router. ipconfig /flushdns (Windows); sudo dscacheutil -flushcache (Mac); restart the browser. Then check the TTL expired.
  2. Which DNS is the device using? ipconfig /all (Windows) / check the network details. If it's not your local DNS, the local record never gets asked. Fix the DHCP-advertised DNS server.
  3. Split-horizon confusion: the name resolves to the public address while you're inside. That works only if hairpin NAT works on your router; the inside answer (see DNS at Home) is the robust fix.

The internet is down (whole house)

  1. One device or all? One → it's that device (reboot it, check its Wi-Fi). All → it's the router or the ISP.
  2. Read the router's lights / status page. No WAN address, or a 169.254.x.x address on the WAN → the router isn't getting anything from the ISP. (169.254.x.x is the \"I asked for an address and nobody answered\" range.)
  3. Power-cycle in order: ISP modem/gateway off 60 seconds → on, wait for its lights to settle → router off 30 seconds → on. Order matters: the router can't get an address from a modem that's still booting.
  4. Still down? Plug a laptop directly into the modem (if separate). Works → your router is the fault. Doesn't → call the ISP; it's their side.

When to stop and ask

If you've worked a symptom's list twice with no change, stop — you're now in \"change random settings\" territory, which creates second problems. Write down what's actually happening (addresses, what's reachable, what's not, what changed recently) and bring that note to whoever helps you. \"The internet is broken\" gets shrugs; \"laptop is 192.168.1.42, can ping the router, can't resolve names since Tuesday\" gets answers.

Next: Glossary