Bulk email, SMTP Outgoing IP Rotator using iptables

 

i got 5 Public IPs. i’m Gonna configure them, so Postfix can use multiple interfaces/ips for outgoing smtp connections.

First we need creating Interface aliases for those 5 public IPs.

 

# cd /etc/sysconfig/network-scripts/

# cp ifcfg-eth0 ifcfg-eth0:1

Edit ifcfg-eth0:1

 

# vi ifcfg-eth0\:1

 

DEVICE=eth0 <-- default device

HWADDR=XX:XX:XX:XX:XX:XX

ONBOOT=yes

TYPE=Ethernet

BOOTPROTO=none

IPADDR=202.XXX.XX.2 <-- default eth0 IP address

PREFIX=24

GATEWAY=202.XXX.XX.1

DNS1=202.XXX.XX.XX

Change DEVICE and IPADDR parameters

 

DEVICE=eth0:1 <-- device alias #1

HWADDR=XX:XX:XX:XX:XX:XX

ONBOOT=yes

TYPE=Ethernet

BOOTPROTO=none

IPADDR=202.XXX.XX.3 <-- IP alias #1

PREFIX=24

GATEWAY=202.XXX.XX.1

DNS1=202.XXX.XX.XX

 

We can continue with next interfaces for IP aliases same way as mention above.
when we were done, bring those IP aliases up.

#ifup eth0:1

#ifup eth0:2

#ifup eth0:3

#ifup eth0:4

......

next interfaces

 

#ifconfig

eth0      Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX 

          inet addr:202.XXX.XX.2  Bcast:202.XXX.XX.255  Mask:255.255.255.0

          inet6 addr: fe80::20c:29ff:feb0:e91/64 Scope:Link

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

          RX packets:598678 errors:0 dropped:0 overruns:0 frame:0

          TX packets:26348 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:1000

          RX bytes:49088016 (46.8 MiB)  TX bytes:7707579 (7.3 MiB)

 

eth0:1    Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX 

          inet addr:202.XXX.XX.3  Bcast:202.XXX.XX.255  Mask:255.255.255.0

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

 

eth0:2    Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX 

          inet addr:202.XXX.XX.4  Bcast:202.XXX.XX.255  Mask:255.255.255.0

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

 

eth0:3    Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX 

          inet addr:202.XXX.XX.5  Bcast:202.XXX.XX.255  Mask:255.255.255.0

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

 

......

and so on

There’s no particular configuration need to adjust in postfix.
Now the iptables part.make sure your iptables support for statistic match module

# iptables -m statistic -h

......

......

......

statistic match options:

 --mode mode                    Match mode (random, nth)

 random mode:

 --probability p                 Probability

 nth mode:

 --every n                       Match every nth packet

 --packet p                      Initial counter value (0 <= p <= n-1, default 0)

Next continue with iptables rule for rotating source IP addresses.

# iptables -t nat -I POSTROUTING -m state --state NEW -p tcp --dport 25 -o eth0 -m statistic --mode nth --every 5 -j SNAT --to-source 202.XXX.XX.2 # iptables -t nat -I POSTROUTING -m state --state NEW -p tcp --dport 25 -o eth0 -m statistic --mode nth --every 5 -j SNAT --to-source 202.XXX.XX.3 # iptables -t nat -I POSTROUTING -m state --state NEW -p tcp --dport 25 -o eth0 -m statistic --mode nth --every 5 -j SNAT --to-source 202.XXX.XX.4 # iptables -t nat -I POSTROUTING -m state --state NEW -p tcp --dport 25 -o eth0 -m statistic --mode nth --every 5 -j SNAT --to-source 202.XXX.XX.5 # iptables -t nat -I POSTROUTING -m state --state NEW -p tcp --dport 25 -o eth0 -m statistic --mode nth --every 5 -j SNAT --to-source 202.XXX.XX.6