RaspberryPi:DebuggingConnectivity

Debugging Connections

This section is a work in progress. As more common issues are reported by students, this section will be expanded. It's important to note that most connectivity problems come down to an incorrectly configured file, where you may have missed a space, or misspelled something.

Note for Windows Users

If you are having trouble accessing the internet from your Pi using the Ethernet Passthrough technique, it’s likely the Windows bridge needs a reset. Change the IPv4 address of your Ethernet port to “Obtain an IP address automatically”, then on your WiFi connection, disable sharing, click okay, and then re-enable sharing. Go back to the IP configuration of your Ethernet post, and double check the IP to see if it’s been assigned 192.168.137.1. If not, you will need to change it using the “Advanced settings” button.

Ping

Ping sends a packet to a particular host (in this case the Pi), and measures the time taken for a response from that host.

To use the ping command, open a command prompt window or terminal and type the following:

$ ping 192.168.137.15

If that host is unreachable (the Pi hasn’t booted yet or is incorrectly configured), a message will show that the host is unreachable. If everything was correctly configured, you should get

Reply from 192.168.137.15: bytes=32 time<1ns TTL=64

This means your Pi and computer are both correctly configured.

NB: Don’t be surprised if you can’t ping a Windows machine from your Pi. Windows blocks the specific type of packet required for a ping in the firewall.

WiFi

See if you can see wireless networks.

$ iwlist wlan0 scan

If you cannot connect via WiFi, enter into a shell on the Pi and run:

$ journalctl -u wpa_supplicant | grep wlan0
$ journalctl -u dhcpcd.service | grep wlan0

This will output the log files and notify you of any incorrect configurations in wpa_supplicant.

The following command will force the interface to be up (if it can be):

sudo ifconfig wlan0 up

If all else fails, reboot and try again. Some services can be restarted without restarting the Pi, for example:

sudo systemctl restart dhcpcd

Test wpa_supplicant config by killing the process, and running it in debug mode:

sudo killall wpa_supplicant
sudo /sbin/wpa_supplicant -d -c/etc/wpa_supplicant/wpa_supplicant.conf -Dnl80211,wext -iwlan0

"Failure resolving URLs" or "unknown host"

If you try to ping a website from the Pi and it fails, but pinging a IP such as 8.8.8.8 works as expected, it is likely an issue with DNS configuration. Open the resolv.conf file:

$ sudo nano /etc/resolv.conf

And edit it to read the following:

nameserver 8.8.8.8
nameserver 192.168.137.1

8.8.8.8 is the IP of Google’s DNS server. A DNS (Domain Name Service) server is responsible for converting human-readable addressed (for example google.co.za) to something the network architecture can understand (172.217.170.67, in this example).

If you still get this error, try running the following command:

$ sudo route add default gw 192.168.137.1

Where the IP supplied is the IP of the computer or router you are connected to.