[LARTC] Two outbound internet links, using one network interface

[Dashamir Hoxha]

Pio Mendez wrote:
>
>  
>
>     >Pio Mendez wrote:
>     >>PREROUTING chain is not traversed by local traffic, but OUTPUT
>     >>chain does.
>     >
>     >I think that OUTPUT is traversed after routing decision is taken, so
>     >it is still the same problem.
>
>
>     I'm using OUTPUT chain in production environment to balance squid
>     box traffic between 2 ISP, so I'm sure that you can reroute output
>     packets using mangle OUTPUT chain.
>
>     After traversing mangle and nat OUTPUT chains there is another
>     routing process. Please check this diagram:
>
>     http://www.imagestream.com/~josh/PacketFlow.png
>     <http://www.imagestream.com/%7Ejosh/PacketFlow.png>
>
Pio Mendez is right. I have just tested it and it works.
Now the script becomes something like this:

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ip link set eth0 up
ip address flush eth0
ip address add $IP1 dev eth0
ip address add $IP2 dev eth0

route add to default via $GATEWAY1

ip route flush table 2
ip route show table main | grep -Ev ^default \
 | while read ROUTE ; do ip route add table 2 $ROUTE ; done
ip route add table 2 default via $GATEWAY2

ip rule del fwmark 2 table 2   2>/dev/null
ip rule add fwmark 2 table 2

iptables -t mangle -N MARK-RULES
iptables -t mangle -A PREROUTING -j MARK-RULES
iptables -t mangle -A OUTPUT -j MARK-RULES

PORT_LIST="22 53"
for PORT in $PORT_LIST
do
 iptables -t mangle -A MARK-RULES -m tcp -p tcp -dport $PORT -j MARK 
--set-mark 0x2
done

iptables -t nat -A POSTROUTING -o eth0 -m mark --mark 0x2 -j SNAT 
--to-source $IP2
iptables -t nat -A POSTROUTING -o eth0 -j SNAT --to-source $IP1
------------8<---------------------------------