Persist bridge-nf-call-iptables on Reboot

enable_bridge_netfilter.sh

#!/bin/bash

set -e

# Running `modprobe br_netfilter` does not persist.
echo 'br_netfilter' >> /etc/modules

# Running `sysctl net.bridge.bridge-nf-call-iptables=1` does not persist.
echo 'net.bridge.bridge-nf-call-iptables=1' >> /etc/sysctl.conf
echo 'net.bridge.bridge-nf-call-ip6tables=1' >> /etc/sysctl.conf

If this still doesn't work, try sudo apt remove --purge ufw, as ufw has rules that override sysctl.

If that still doesn't work, try sudo grep -rl net.bridge.bridge-nf-call-iptables /etc to find any other files that could be overriding it.