Pi-hole, Google Wifi, and Device Names

One of the things that bothered me for quite some time with my Pi-Hole was that using it with Google Wifi (first gen), it wouldn’t automatically detect device hostnames. I’d done a lot of googling and never could get it to work even after a lot of different trials with multiple settings.

Eventually I gave up and instead wrote a command that would use nmap to help fill in the gaps, and output to /etc/pihole/custom.list:

if [ "$(id -u)" != "0" ]; then
	echo "This script must be run as root" 1>&2
	exit 1

echo -n "Looking up MAC and IPs"
for ip in "" "" ""; do
	echo -n .
	# This is very slow.
	nmap -sP "$ip"/20 > "$ip"-nmap.txt

# Mega-command to turn the nmap output into a CSV.
cat 192.168.?.0-nmap.txt \
	| sed '/^Starting Nmap/ d' \
	| sed '/^Host is up/ d' \
	| sed '/^Stats:/ d' \
	| sed '/^Ping Scan Timing:/ d' \
	| sed '/^Nmap done:/ d' \
	| sed -z 's/\nMAC/,MAC/g' \
	| sed -e 's/Nmap scan report for //g' \
	| sed -e 's/MAC Address: //g' \
	| sed -e 's/ (/,(/g' \
	| grep -Ev $'^[0-9.]+$' \
	| sort -u > ip-mac-mapping.csv

rm /etc/pihole/custom.list 2> /dev/null
while IFS=, read -r col1 col2 col3
	# Strip out opening and closing parenthesis.

	# Replace all non-alphanumeric characters with dashes.

	# Manually name some of the MACs I already know.
	case "$col2" in
		echo -n

	# For some reason, this one is still funky, so I'm adding in a special case for it.
	# Could have just been weird caching during my testing.
	case "$col1" in
		echo -n

	# The PiHole custom.list is supposed to follow the hosts standard, but it seems that
	# it is not happy with tabs and comments :sadpanda:
	echo "$col1	$col3 # $col2"
	echo "$col1 $col3" >> /etc/pihole/custom.list
done < ip-mac-mapping.csvCode language: PHP (php)

This will attempt to grab some info about all the devices on your network via nmap, but also allow you to manually override that per IP or per MAC. I have of course stripped out some devices and semi-anonymized my MACs in the above example.

The nmap can be pretty slow, especially if you’re running this on a first gen Raspberry Pi like I am.

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