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amitbareket

Member

Registered: 2014-11-26

Posts: 1

IPTABLES POSTROUTING Load balancing help

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

branch

Member

Registered: 2014-03-16

Posts: 209

Re: IPTABLES POSTROUTING Load balancing help

I havn't tried this, but I would let the routing table do the load balancing for outgoing packets and match the source addresses to the outgoing interface so that responses always come from the same interface a request went out. So the iptables rules would look something like:
-A POSTROUTING -o x1 -s 10.8.0.0/24 -j SNAT --to-source x1.x1.x1.x1
-A POSTROUTING -o x2 -s 10.8.0.0/24 -j SNAT --to-source x2.x2.x2.x2
etc.

fukawi2

Ex-Administratorino

From: .vic.au

Registered: 2007-09-28

Posts: 6,231

Website

Re: IPTABLES POSTROUTING Load balancing help

I haven't tested, but this should do it:

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 5 --packet 1 -j SNAT --to x2
iptables -t nat -A OUTPUT_LB -m statistic --mode nth --every 5 --packet 2 -j SNAT --to x3
iptables -t nat -A OUTPUT_LB -m statistic --mode nth --every 5 --packet 3 -j SNAT --to x4
iptables -t nat -A OUTPUT_LB -m statistic --mode nth --every 5 --packet 4 -j SNAT --to x5
iptables -t nat -A OUTPUT -m state --state NEW -j OUTPUT_LB

Alternatively, but this may lead to bias towards x5:

iptables -t nat -N OUTPUT_LB
iptables -t nat -A OUTPUT_LB -m statistic --mode random --probability 0.2 -j SNAT --to x1
iptables -t nat -A OUTPUT_LB -m statistic --mode random --probability 0.2 -j SNAT --to x2
iptables -t nat -A OUTPUT_LB -m statistic --mode random --probability 0.2 -j SNAT --to x3
iptables -t nat -A OUTPUT_LB -m statistic --mode random --probability 0.2 -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

Last edited by fukawi2 (2014-11-30 22:03:56)

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aesiris

Member

Registered: 2012-02-25

Posts: 97

Re: IPTABLES POSTROUTING Load balancing help

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

fukawi2

Ex-Administratorino

From: .vic.au

Registered: 2007-09-28

Posts: 6,231

Website

Re: IPTABLES POSTROUTING Load balancing help

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 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

Yes, my maths aren't the greatest, but that makes sense. I think using nth would still be more even, depends if the OP really wants "random" balancing, or just load-balancing.

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