To change the default network for docker

setup-bridge.sh

#!/bin/bash -e

IFADDR="192.168.3.1/24"

if [[ ! ip link show docker0 ]]; then
  ip link add docker0 type bridge
  ip addr add "$IFADDR" dev docker0
  ip link set docker0 up
  iptables -t nat -A POSTROUTING -s "$IFADDR" ! -d "$IFADDR" -j MASQUERADE
fi

echo 1 > /proc/sys/net/ipv4/ip_forward 

teardown-bridge.sh

#!/bin/bash -e

iptables -t nat -F
ifconfig docker0 down
brctl delbr docker0