重装Ubuntu后无法连接家庭WiFi，DHCP疑似故障（静态IP可用）

Hey there, I’ve dealt with this exact kind of head-scratcher before—reinstalling Ubuntu, only to have your home WiFi refuse to connect via DHCP while other networks work fine. Let’s walk through some practical fixes to get this sorted:

1. Verify NetworkManager & DHCP Service Status #

First, make sure the core network service is running properly:

• Open a terminal and check NetworkManager’s status:

  sudo systemctl status NetworkManager
  

• If you see it’s inactive or throwing errors, restart and enable it:

  sudo systemctl start NetworkManager
  sudo systemctl enable NetworkManager
  

  This ensures the service starts automatically on boot too.

2. Reset NetworkManager Configuration #

Old cached settings from your previous install might be interfering. Let’s wipe them clean:

• Back up existing configs first (just in case):

  sudo mv /etc/NetworkManager/NetworkManager.conf /etc/NetworkManager/NetworkManager.conf.bak
  sudo mv /var/lib/NetworkManager /var/lib/NetworkManager.bak
  

• Restart NetworkManager to generate fresh configs:

  sudo systemctl restart NetworkManager
  

  Now try connecting to your home WiFi again.

3. Switch to a Different DHCP Client #

Ubuntu uses dhclient by default, but sometimes swapping to dhcpcd resolves compatibility issues with certain routers:

• Install dhcpcd5:

  sudo apt update && sudo apt install dhcpcd5
  

• Modify NetworkManager to use this new client:

  sudo nano /etc/NetworkManager/NetworkManager.conf
  

  Add this line under the [main] section:

  dhcp=dhcpcd
  

• Save the file (press Ctrl+O, hit Enter, then Ctrl+X), then restart NetworkManager:

  sudo systemctl restart NetworkManager
  

4. Troubleshoot Your Home Router #

Don’t rule out the router being the culprit—even if it worked before:

• Reboot the router: Unplug it for 30 seconds, plug it back in, and wait 5 minutes before testing the connection.
• Check DHCP pool limits: Log into your router’s admin panel (usually at 192.168.1.1 or 192.168.0.1) and make sure the DHCP address pool isn’t full. If it is, expand the range or release unused IPs.
• Verify MAC filtering: If your router has MAC address filtering enabled, confirm your Ubuntu machine’s WiFi MAC address is on the allowed list. You can find your MAC with:

  ip link show | grep wlan0
  

  (Replace wlan0 with your actual WiFi interface name if needed.)

5. Diagnose DHCP Traffic with Packet Capture #

To narrow down where the issue lies, capture DHCP traffic:

• Run this command in the terminal (replace wlan0 with your WiFi interface):

  sudo tcpdump -i wlan0 port 67 or port 68
  

• Try connecting to your home WiFi while the capture runs. You’ll see:
  • If you see DHCPDISCOVER messages but no DHCPOFFER, the router isn’t responding—focus on router troubleshooting.
  • If you don’t see any DHCPDISCOVER messages at all, the problem is on the Ubuntu side, so revisit the earlier steps.

6. Manually Specify DHCP Server Address #

If all else fails, force your Ubuntu machine to use your router as the DHCP server:

• Open Network Settings, select your home WiFi network, and click "Settings".
• Go to the IPv4 tab, change the method from "Automatic (DHCP)" to "Automatic (DHCP) addresses only".
• In the "DHCP server" field, enter your router’s IP address (usually 192.168.1.1 or 192.168.0.1).
• Save the settings and reconnect.

内容的提问来源于stack exchange，提问作者James B