Using iptables to forward traffic destined for specific ip via specific interface

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http://serverfault.com – I want to forward traffic destined for a specific ip from my internal network via a specific interface. I have two interfaces which are currently load balanced. I need all requests for a certain ip to go out via eth0 otherwise my external ip changes and sessions are dropped. eg. all requests from to ip on port 443 must go out via interface eth0. How can I do this with iptables? (HowTos)