Configures a secondary network interface (Debian Jessie)

nic.sh

#!/bin/bash

set -e

gateway_ip=$(ip route show default | awk '/default/ {print $3}')
eth1_ip=$(ip addr show eth1 | grep "inet\b" | awk '{print $2}' | cut -d/ -f1)

echo "Configuring secondary IP (eth1) ..."

# Print stuff
echo "Gateway IP: ${gateway_ip}"
echo "Secondary IP: ${eth1_ip}"

# Enable DHCP autoconfiguration
if ! grep -q "auto eth1" /etc/network/interfaces; then
  sed -i '/auto eth0/a auto eth1' /etc/network/interfaces
  echo ".. dhcp autoconfigure enabled"
else
  echo ".. dhcp autoconfigure already enabled, skipping"
fi

# Restart networking service
echo ".. restarting network service"
service networking restart

# Add an entry to the route table
if ! grep -q "eth1_rt" /etc/iproute2/rt_tables; then
  echo "2 eth1_rt" >> /etc/iproute2/rt_tables
  echo ".. route table entry added"
else
  echo ".. route table entry exists, skipping"
fi

# Add the default route for eth1
if ! ip route list table eth1_rt 2>/dev/null | grep -q ${gateway_ip}; then
  ip route add default via ${gateway_ip} dev eth1 table eth1_rt
  echo ".. default route added"
else
  echo ".. default route exists, skipping"
fi

# Add rule to route traffic with a source of "eth1_ip" to the eth1 route table
if ! ip rule show | grep -q ${eth1_ip}; then
  ip rule add from ${eth1_ip} lookup eth1_rt prio 1000
  echo ".. ip rule added"
else
  echo ".. ip rule exists, skipping"
fi

echo "Configuration complete!"