From mboxrd@z Thu Jan  1 00:00:00 1970
From: Cong Wang <xiyou.wangcong@gmail.com>
Subject: Re: Question: routing packets via specific router in LAN?
Date: Mon, 3 Sep 2012 08:28:37 +0000 (UTC)
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On Mon, 03 Sep 2012 at 06:04 GMT, Yi Li <lovelylich@gmail.com> wrote:
> Hi All,
> I have server --- router ---client three machines,
> and they all have only one ip in the same LAN.
> I want to instruct the packets flowing through the router when the
> server and client communicates.
> I have do the following things to setup:
> on the server:
> # ip route add to unicast CLIENT_IP/32 via ROUTER_IP dev eth0
> # echo 0 > /proc/sys/net/ipv4/conf/all/accept_redirects
> # echo 0 > /proc/sys/net/ipv4/conf/eth0/accept_redirects
>
> on the client:
> /*modify route table*/
> # ip route add to unicast SERVER_IP/32 via ROUTER_IP dev eth0
> /*disable icmp-redirects accept*/
> # echo 0 > /proc/sys/net/ipv4/conf/all/accept_redirects
> # echo 0 > /proc/sys/net/ipv4/conf/eth0/accept_redirects
>
> on the router:
> /*enable forwarding*/
> # echo 1 > /proc/sys/net/ipv4/ip_forwarding
> /*disable icmp-redirects*/
> # echo 0 > /proc/sys/net/ipv4/conf/all/send_redirects
> # echo 0 > /proc/sys/net/ipv4/conf/eth0/send_redirects
>

Try to add some iptables rules like:

iptables -A FORWARD -j ACCEPT -s CLIENT_IP/xx -d  SERVER_IP/xx