IP ALIASING ON A LINUX MACHINE
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Edit /etc/rc.d/rc.local:

#IP aliased                                       
/sbin/ifconfig lo 127.0.0.1
/sbin/ifconfig eth0 up
/sbin/ifconfig eth0 172.16.3.1
/sbin/ifconfig eth0:0 172.16.3.10
/sbin/ifconfig eth0:1 172.16.3.100
          
#IP routed       
/sbin/route add -net 127.0.0.0
/sbin/route add -net 172.16.3.0 dev eth0
/sbin/route add -host 172.16.3.1 dev eth0
/sbin/route add -host 172.16.3.10 dev eth0:0
/sbin/route add -host 172.16.3.100 dev eth0:1
/sbin/route add default gw 172.16.3.200

172.16.3.1 is the main IP #, while .10 and .100 are the aliases.
eth0:x where x=0,1,2,...n (max=256) is for the different IP #s.