Props to this site for the helpful info.
1. Configure your first static IP Address and Gateway information as normal inside of /etc/network/interfaces. If you have multiple static IP’s in the same subnet using the same gateway you should be fine to add them as sub-interfaces with no problems.
auto eth0
iface eth0 inet static
address 1.1.1.1
netmask 255.255.255.0
network 1.1.1.0
broadcast 1.1.1.255
dns-nameservers 2.2.2.2 3.3.3.3
dns-search yourdomain.com
gateway 1.1.1.2
2. Configure your additional static IP Addresses but leave off the Gateway information inside of /etc/network/interfaces – Linux will squawk at this
auto eth1
iface eth1 inet static
address 4.4.4.4
netmask 255.255.255.0
network 4.4.4.0
broadcast 4.4.4.255
auto eth1:1
iface eth1:1 inet static
address 5.5.5.5
netmask 255.255.255.0
network 5.5.5.0
broadcast 5.5.5.255
3. Restart Networking
4. Create a routing policy number and name for each additional static IP/Gateway combo. I will create two for this example.
echo "1 ether1" >> /etc/iproute2/rt_tables echo "2 ether1_1" >> /etc/iproute2/rt_tables
5. Add IP Routes for each of your Policies. Insert your Default Gateway after “default via”. You will want to add the entries in step numbers 5 and 6 to /etc/rc.local to retain the routes after a reboot.
ip route add 4.4.4.4/24 dev eth1 src 4.4.4.4 table ether1 ip route add default via 4.4.4.254 dev eth1 table ether1 ip route add 5.5.5.5/24 dev eth1:1 src 5.5.5.5 table ether1_1 ip route add default via 5.5.5.254 dev eth1:1 table ether1_1
6. Create To and From IP Rules for your entries
ip rule add from 4.4.4.4/32 table ether1 ip rule add to 4.4.4.4/32 table ether1 ip rule add from 5.5.5.5/32 table ether1 ip rule add to 5.5.5.5/32 table ether1
7. Useful commands for checking your routes and policies are:
netstat -anr ip rule show ip route show table ether1