can single linux box with dual gateway provide two separate connection ?

["J. Bakshi" <joydeep@infoservices.in>]

Hello list,

This is not the traditional load-balancing or fail over technique which
I like to achieve through iptables but the objective is different.  I
have 2 different ISP connections. The Linux server is presently using
one ISP as well as do ip-forward to make it available for the LAN
users.  I have achieved this by

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

iptables -A FORWARD -i ${WAN_IFACE} -o ${LAN_IFACE} -s 192.168.0.0/24 -m \
conntrack --ctstate NEW -j ACCEPT
iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
iptables -A POSTROUTING -t nat -j MASQUERADE
` ` `

cool. Now Some thing extra which I like to achieve. I like to put the
second ISP too into the server and use the above style iptables to
forward it to another lan card so that both the connection will be
available *separately* from the same server. Obviously server can choose
any one of these as its own gateway. Got the idea ? not a load-balancing
setup but the server will act as two separate modem actually to provide
two connections. I have followed

 http://www.generationip.com/documentation/network-documentation/93-howto-setup-multi-default-gateway-on-linux


to configure the routing tables for these two ISPs. Frankly telling you
I have become a little confused now. Shall I now simply apply the above
iptable rules for the two connections or some thing more is required to
achieve this ? Obviously I can continue doing experiment to know the
answer but the server where I am working is acting as the default
gateway;  hence my liberty is also restricted to do this very
experiment.  could any one help me out to come out from this very
confusing stage ?
Thanks

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