Objective

Add two network interface in ubuntu 12.04 in aws and route traffic properly to either ip

Scope: Amazon EC2 Attach Elastic Network Interface (VPC)

Process

Start AMI in VPC
After boot attach secondary nic
Ensure both nic’s have an external IP associated with it
configure new /etc/network/interfaces
restart networking
stop network-manger
ssh back in (ssh will flip to the other elastic ip)
add new ip route
flush ip route table
restart networking

Manual Howto

# /etc/network/interfaces
# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet dhcp

auto eth1
iface eth1 inet static
address 10.1.0.102
netmask 255.255.255.0
network 10.1.0.0
broadcast 10.1.0.255

Now run:

echo "network manager stop may make the ssh connect flap to the other nic"
stop network-manager
/etc/init.d/networking restart
netstat -rn

If you’d like traffic that arrives on eth1 to also exit on eth1 (if your default route happens to be on eth0) then follow these steps:

Note: We are assuming in this scenario that eth1’s ip address is 10.1.0.102

echo "creating a new policy routing table entry within the /etc/iproute2/rt_tables"
echo "1 admin" >> /etc/iproute2/rt_tables

echo "adding entries to our new admin table"
ip route add 10.1.0.0 dev eth1 src 10.1.0.102 table admin
ip route add default via 10.1.0.1 dev eth1 table admin

echo "view of ip rule table before change are applied"
ip rule

echo "applying the rules on the admin table"
ip rule add from 10.1.0.102/32 table admin
ip rule add to 10.1.0.102/32 table admin

echo "view of ip rule table after change are applied"
ip rule

echo "flushing ip routing cache"
ip route flush cache

Example Script

#!/bin/bash
#
# Author: Steve Stonebraker
# Name: aws_fix_dual_nic_routing.sh
# url: https://github.com/ssstonebraker/braker-scripts/blob/master/working-scripts/aws_fix_dual_nic_routing.sh
# Requirement:
# -Two interfaces assigned in the AWS control panel and a private ip for each
# -Both interfaces should appear when typing ifconfig
# 
# Description:
# Script will:
# 1. Generate your new static /etc/network/interfaces
# 2. Restart networking
# 3. If you get an error then at this point you need to "stop network-manager" (ssh will probably flap to the other ip)
# 4. If ssh flapped then run the script again and ip route table will be set up properly

########################################
function print_status ()
{
    echo -e "\x1B[01;34m[*]\x1B[0m $1"
}

function print_good ()
{
    echo -e "\x1B[01;32m[*]\x1B[0m $1"
}

function print_error ()
{
    echo -e "\x1B[01;31m[*]\x1B[0m $1"
}

function print_notification ()
{
  echo -e "\x1B[01;33m[*]\x1B[0m $1"
}
function printline() {
hr=---------------------------------------------------------------\
----------------------------------------------------------------
printf '%s\n' "${hr:0:${COLUMNS:-$(tput cols)}}"
}
function proceed_if_root()
{
#Make sure only root can run our script
        if [[ $EUID -ne 0 ]]; then
           print_error "This script must be run as root" 1>&2
           exit 1
        fi
}
declare -i state_ok=0
declare -i state_warning=1
declare -i state_critical=2
declare -i state_unknown=3
declare -i state_dependent=4

# Make sure ip and egrep commands are valid
if [[ ! -x "$(type -p ip 2>/dev/null)" ]]; then
    echo "ERROR: 'ip' not executable"
    exit ${state_unknown}
fi

if [[ ! -x "$(type -p egrep 2>/dev/null)" ]]; then
    echo "ERROR: 'egrep' not executable"
    exit ${state_unknown}
fi


function system_is_link_up () {
  #determines if interface is up
  iface=$1
  ip link show dev ${iface} >&/dev/null
  if [ "$?" != "0" ]; then
    echo "CRITICAL - interface '${iface}' does NOT EXIST!"
    exit 2
  fi
  ip addr show dev ${iface} 2>/dev/null |  egrep "[[:space:]]${iface}:.*(,|<)UP(,|>)"  >&/dev/null
  if [ "$?" != "0" ]; then
    echo "CRITICAL - interface '${iface}' is not up"
    exit 2
  fi
  print_good "OK - ${iface} is configured and is UP"
}
function system_print_ip_for_interface {
  # returns the  IP assigned to interface passed
  # ex: system_print_ip_for_interface eth0
  echo $(ifconfig $1 | awk -F: '/inet addr:/ {print $2}' | awk '{ print $1 }')
}
function system_print_broadcast_for_interface {
  # returns the  IP assigned to interface passed
  # ex: system_print_ip_for_interface eth0
  echo $(/sbin/ifconfig $1 | grep 'inet addr:' | cut -d: -f3 | awk '{ print $1}')
}
function system_print_mask_for_interface {
  # returns the  IP assigned to interface passed
  # ex: system_print_ip_for_interface eth0
  echo $(/sbin/ifconfig $1 | grep 'inet addr:' | cut -d: -f4 | awk '{ print $1}')
}
function system_dns_search_domain {
  # returns the primary IP assigned to eth0
  echo $(grep "search" /etc/resolv.conf | cut -d' ' -f2)
}

system_is_link_up "eth0"
system_is_link_up "eth1"



proceed_if_root

#eth0
eth0IP=`system_print_ip_for_interface "eth0"`
eth0Broadcast=`system_print_broadcast_for_interface "eth0"`
eth0Mask=`system_print_mask_for_interface "eth0"`

#eth1
eth1IP=`system_print_ip_for_interface "eth1"`
eth1Broadcast=`system_print_broadcast_for_interface "eth1"`
eth1Mask=`system_print_mask_for_interface "eth1"`
eth1route=$(ip route | grep "default" |  cut -d " " -f3 | uniq)

#get network
IP=$(ifconfig eth1 | grep Mask | cut -d ':' -f2 | cut -d " " -f1)
Mask=$(ifconfig eth1 | grep Mask | cut -d ':' -f4 | cut -d " " -f1)
IFS=.
IPArray=($IP)
MaskArray=($Mask)
NetArray=()
Start=0
Max=$(( 255 * 255 * 255 * 255 ))
for key in "${!IPArray[@]}";
do
   NetArray[$key]=$(( ${IPArray[$key]} & ${MaskArray[$key]} ))
   Start=$(( $Start + (${NetArray[$key]} << (3-$key)*8) ))
done
IFS=

eth1Network="${NetArray[0]}.${NetArray[1]}.${NetArray[2]}.${NetArray[3]}"

dnsSearchDomain=`system_dns_search_domain`
print_status "eth0 info"
print_notification $eth0IP
print_notification $eth0Broadcast
print_notification $eth0Mask
printline
print_status "eth1 info"
print_notification $eth1IP
print_notification $eth1Broadcast
print_notification $eth1Mask
echo $eth1Network
printline
print_status "dns name servers"
printline
echo "" > /tmp/nameservers.tmp
  # if the user didn't provide a FQDN then just append hostname they provided


for nameserver in $(/bin/egrep \
'\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b' \
/etc/resolv.conf \
| /usr/bin/cut -d: -f2 \
| awk '{ print $2}'); do
printf " %s" "$nameserver" >> /tmp/nameservers.tmp
done

printedNameservers=$(sed ':a;N;$!ba;s/\n/ /g' /tmp/nameservers.tmp)

print_status "dns search domain"
print_notification "${dnsSearchDomain}"
printline
print_status "proposed /etc/network/interfaces file"
cat <<EOF > /tmp/proposed.interfaces
# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet dhcp

auto eth1
iface eth1 inet static
address ${eth1IP}
netmask ${eth1Mask}
network ${eth1Network}
broadcast ${eth1Broadcast}

dns-nameservers${printedNameservers}
dns-search ${dnsSearchDomain}
EOF

cat /tmp/proposed.interfaces

print_status "changing /etc/network/interfaces"
mv /tmp/proposed.interfaces /etc/network/interfaces

printline
print_good "restarting networking"
/etc/init.d/networking restart

print_status "If you got an error that is okay - you need to stop nework manager"
echo "ex: stop network-manager"


##Then to ensure that traffic that arrives on eth1 also exists on eth1:
printline
print_status "creating a new policy routing table entry within the /etc/iproute2/rt_tables"
echo "1 admin" >> /etc/iproute2/rt_tables

print_status "adding entries to our new admin table"
ip route add ${eth1Network} dev eth1 src ${eth1IP} table admin
ip route add default via ${eth1route} dev eth1 table admin

print_status "view of ip rule table before change are applied"
printline
ip rule
printline

print_status "view of routing table before changes are applied"
printline
netstat -rn
printline

print_status "applying the rules on the admin table"
ip rule add from ${eth1IP}/32 table admin
ip rule add to ${eth1IP}/32 table admin
# /sbin/ip rule del from 192.168.0.0/26 table 200

print_status "flushing ip routing cache"
ip route flush cache

print_status "view of ip rule table after change are applied"
printline
ip rule
printline

print_status "view of routing table after changes are applied"
printline
netstat -rn
printline

Example Script Output

[*] changing /etc/network/interfaces
----------------------------------------------------------------------------------------------
[*] restarting networking
 * Running /etc/init.d/networking restart is deprecated because it may not enable again some interfaces
 * Reconfiguring network interfaces...
ssh stop/waiting
ssh start/running, process 7092
ssh stop/waiting
ssh start/running, process 7225
   ...done.
[*] If you got an error that is okay - you need to stop nework manager
----------------------------------------------------------------------------------------------
[*] creating a new policy routing table entry within the /etc/iproute2/rt_tables
[*] adding entries to our new admin table
[*] view of ip rule table before change are applied
----------------------------------------------------------------------------------------------
0:      from all lookup local
32766:  from all lookup main
32767:  from all lookup default
----------------------------------------------------------------------------------------------
[*] view of routing table before changes are applied
----------------------------------------------------------------------------------------------
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
0.0.0.0         172.31.32.1     0.0.0.0         UG        0 0          0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth0
172.31.32.0     0.0.0.0         255.255.240.0   U         0 0          0 eth0
172.31.32.0     0.0.0.0         255.255.240.0   U         0 0          0 eth1
----------------------------------------------------------------------------------------------
[*] applying the rules on the admin table
[*] flushing ip routing cache
[*] view of ip rule table after change are applied
----------------------------------------------------------------------------------------------
0:      from all lookup local
32764:  from all to 172.31.32.101 lookup admin
32765:  from 172.31.32.101 lookup admin
32766:  from all lookup main
32767:  from all lookup default
----------------------------------------------------------------------------------------------
[*] view of routing table after changes are applied
----------------------------------------------------------------------------------------------
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
0.0.0.0         172.31.32.1     0.0.0.0         UG        0 0          0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth0
172.31.32.0     0.0.0.0         255.255.240.0   U         0 0          0 eth0
172.31.32.0     0.0.0.0         255.255.240.0   U         0 0          0 eth1
-----------------------------------------------------------------------------------

Script in Action

aws-add-two-network-interfaces-in-ubuntu-12-04-precise

AWS add two network interfaces in ubuntu 12.04 precise