IPTABLES POSTROUTING Load balancing help

Question

Hi there,
I have an interface with 5 IP addresses assigned to it (as virtual adapters) let's call them x1,x2,x3,x4 and x5.
Currently I have SNAT POSTROUTING forwarding rules from local source range to specific public ip address. Below is an example for the current rule
-A POSTROUTING -s 10.8.0.0/24 -j SNAT --to-source x1.x1.x1.x1
What I would like to achieve is that new established local connections will be postrouted and assigned to one of the IPs above (x1/x2/x3/x4/x5) randomly / round robin. I tired to look for a solution online but I didn't find any information for how to do so. I almost sure its feasible.
Many thanks for your help guys!
Amit

Answer 1

fukawi2 wrote:
I haven't tested, but this should do it:
Alternatively, but this may lead to bias towards x5:
I understand it differently: iptable rules are independent and traversed in order, so the unbiased chain should be
iptables -t nat -N OUTPUT_LB
iptables -t nat -A OUTPUT_LB -m statistic --mode nth --every 5 --packet 0 -j SNAT --to x1
iptables -t nat -A OUTPUT_LB -m statistic --mode nth --every 4 --packet 0 -j SNAT --to x2
iptables -t nat -A OUTPUT_LB -m statistic --mode nth --every 3 --packet 0 -j SNAT --to x3
iptables -t nat -A OUTPUT_LB -m statistic --mode nth --every 2 --packet 0 -j SNAT --to x4
iptables -t nat -A OUTPUT_LB -j SNAT --to x5
iptables -t nat -A OUTPUT -m state --state NEW -j OUTPUT_LB
iptables -t nat -N OUTPUT_LB
iptables -t nat -A OUTPUT_LB -m statistic --mode random --probability 0.20000 -j SNAT --to x1
iptables -t nat -A OUTPUT_LB -m statistic --mode random --probability 0.25000 -j SNAT --to x2
iptables -t nat -A OUTPUT_LB -m statistic --mode random --probability 0.33333 -j SNAT --to x3
iptables -t nat -A OUTPUT_LB -m statistic --mode random --probability 0.50000 -j SNAT --to x4
iptables -t nat -A OUTPUT_LB -j SNAT --to x5
iptables -t nat -A OUTPUT -m state --state NEW -j OUTPUT_LB