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I read this tutorial, however I am considering a method to load balancing for Internet connection by applying iptables rule on 2 interfaces. The following is my iptables rule.

#!/bin/sh



IPT="/sbin/iptables"



LAN='ens38'

WAN='ens33'

OPT='ens37'



LAN_NET="192.168.100.0/24"



$IPT -F

$IPT -X

$IPT -t nat -F



$IPT -P INPUT DROP

$IPT -P OUTPUT DROP

$IPT -P FORWARD DROP





$IPT -A FORWARD -i $LAN -o $WAN -j ACCEPT

$IPT -A FORWARD -i $LAN -o $OPT -j ACCEPT





$IPT -A FORWARD -i $WAN -o $LAN -j ACCEPT

$IPT -A FORWARD -i $OPT -o $LAN -j ACCEPT



$IPT -t nat -A POSTROUTING -o $WAN -j MASQUERADE

$IPT -t nat -A POSTROUTING -o $OPT -j MASQUERADE





# Load balancing rules (Split 50/50 between fwmark 1/2)

$IPT -t mangle -N balance1

$IPT -t mangle -A balance1 -m connmark ! --mark 0 -j RETURN

$IPT -t mangle -A balance1 -m state --state ESTABLISHED,RELATED -j RETURN

$IPT -t mangle -A balance1 -m statistic --mode nth --every 2 --packet 0 -j CONNMARK --set-mark 1

$IPT -t mangle -A balance1 -m statistic --mode nth --every 2 --packet 1 -j CONNMARK --set-mark 2



# Check to see if we have already marked a packet

$IPT -t mangle -A PREROUTING  -m state --state ESTABLISHED,RELATED -j CONNMARK --restore-mark

$IPT -t mangle -A OUTPUT      -m state --state ESTABLISHED,RELATED -j CONNMARK --restore-mark



# Mark incoming connections to return on the interface they came in on

$IPT -t mangle -A PREROUTING          -i $WAN                     -m state --state NEW  -j CONNMARK --set-mark 1

$IPT -t mangle -A PREROUTING          -i $OPT                     -m state --state NEW  -j CONNMARK --set-mark 2



# New outgoing packets

$IPT -t mangle -A PREROUTING  -i $LAN          -p tcp --dport 80 -m state --state NEW  -j balance1

$IPT -t mangle -A PREROUTING  -i $LAN          -p tcp --dport 443 -m state --state NEW  -j balance1

# $IPT -t mangle -A OUTPUT                       -p tcp --dport  80 -m state --state NEW  -j balance1



# Choose our route and save the mark

$IPT -t mangle -A PREROUTING  -m connmark --mark 1 -j MARK --set-mark 1

$IPT -t mangle -A PREROUTING  -m connmark --mark 2 -j MARK --set-mark 2

$IPT -t mangle -A PREROUTING  -m state --state NEW -m connmark ! --mark 0  -j CONNMARK --save-mark





echo 1 > /proc/sys/net/ipv4/ip_forward

I defined 2 table wan and opt in /etc/iproute2/rt_tables like the following:

[root@R1 ~]# cat /etc/iproute2/rt_tables 

#

# reserved values

#

255 local

254 main

253 default

0   unspec

#

# local

#

1   wan

2   opt

This is the script that I add route for iproute:

LAN_DEV='ens38'

WAN_DEV='ens33'

OPT_DEV='ens37'



WAN_GW="192.168.84.2"

OPT_GW="192.168.0.1"



LAN_NET="192.168.100.0/24"





ip rule add fwmark 1 table wan

ip rule add fwmark 2 table opt



# Add default route for table wan and opt

ip route add default via $WAN_GW dev $WAN_DEV table wan

ip route add default via $OPT_GW dev $OPT_DEV table opt



# Add LAN route for table wan and opt



ip route add $LAN_NET dev $LAN_DEV table opt

ip route add $LAN_NET dev $LAN_DEV table wan

As I understood from this guide, restore-mark and save-mark restore and save the packet mark from the connection mark. So the rules apply for every packet in a connection. For example: I have a connection A. iptables rules count every 4 packets in connection A and mark it 1,2,1,2.

How can I mark a connection separately in case I have many connections. For example: I have 3 connections A,B,C and I want to count and mark them like: 1,2,3.

Actually, this rule uses route from WAN (ens33) only. When the packet come in to router. It not route to OPT (ens37) which I can not explain.

You need a rule to accept the connections already known, without re-marking them.

This way, only the new connections will trigger the counter.

iptables -A PREROUTING -t mangle -j CONNMARK --restore-mark

iptables -A PREROUTING -t mangle -m mark ! --mark 0 -j ACCEPT

iptables -A PREROUTING -t mangle -m mark --mark 0 -m nth --counter 1 

--every 3 --packet 1 -j MARK --set-mark 1

iptables -A PREROUTING -t mangle -m mark --mark 0 -m nth --counter 1 

--every 3 --packet 2 -j MARK --set-mark 2

iptables -A PREROUTING -t mangle -m mark --mark 0 -m nth --counter 1 

--every 3 --packet 3 -j MARK --set-mark 3

iptables -A POSTROUTING -t mangle -j CONNMARK --save-mark