How to monitor network traffic on my USG via Wireshark

I’m currently trying to figure out some internal network issues¹ and for that need to monitor the traffic of a specific device on my network. I’m using a Unifi USG as my router (behind the ISP’s Fritzbox that I consider hostile since it’s not mine). I found this post on reddit that explains how to capture traffic on the USG via tcpdump and send it through the SSH session to Wireshark on my laptop:

ssh admin@192.168.1.1 'sudo tcpdump -f -i eth1 -w - src 192.168.1.12' | wireshark -k -i - 

I could confirm that this works and created a small script to make it easier to use by throwing this into ~/.local/bin/gatedump²:

#!/bin/bash

ARGS="$@"
TCPDUMP="sudo tcpdump -f -w - $ARGS"

ssh usg "$TCPDUMP" | wireshark -k -i -

This now allows me to easily run tcpdump remotely with custom arguments, e.g. gatedump -i eth1 host 192.168.1.123, and have it fire up Wireshark automatically. Wish me luck I’ll now be able to figure out what’s going on on my network, because it’s driving me up the wall.

Update from 2023-12-06: In case you are wondering how this story ended, the issue resolved itself with the next OS update of my partner’s iPhone. So whatever caused it, it’s gone now, and I hope for good.