Allows passthrough for bridges, wireless access-point's and range extenders

adapter-passthrough

#!/bin/bash

if [ "$EUID" -ne 0 ]
	then echo "Must be root"
	exit
fi

ADAPTER="eth0"

# Allow overriding from eth0 by passing in a single argument
if [ $# -eq 1 ]; then
    ADAPTER="$1"
fi

#Uncomment net.ipv4.ip_forward
sed -i -- 's/#net.ipv4.ip_forward/net.ipv4.ip_forward/g' /etc/sysctl.conf
#Change value of net.ipv4.ip_forward if not already 1
sed -i -- 's/net.ipv4.ip_forward=0/net.ipv4.ip_forward=1/g' /etc/sysctl.conf
#Activate on current system
echo 1 > /proc/sys/net/ipv4/ip_forward

iptables -t nat -A POSTROUTING -o $ADAPTER -j MASQUERADE  
iptables -A FORWARD -i $ADAPTER -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT  
iptables -A FORWARD -i wlan0 -o $ADAPTER -j ACCEPT

Thanks a lot, I've tried several ways, but finally I just use your code, and it works!

@vicatcu yeah raspbian stretch has some awful decisions including the renaming of adapters. Try working with https://gist.github.com/Lewiscowles1986/390d4d423a08c4663c0ada0adfe04cdb as well to allow you to set /etc/network/interfaces as you've indicated you have here.

Big Picture

• the script accepts an interface, it's documented above, use it for whatever your eth0 is called.
• this is only designed for raspbian without edits (although it should work on most vanilla debian-based distro's)
• the script linked helps get interfaces started if you've edited /etc/network/interfaces in a debian-based distro using the raspbian setup (to skip any networking if a single interface is defined in /etc/network/interfaces ...)