Ping reply not getting to LAN machines but getting in Linux router Gateway

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http://serverfault.com – I have configured Ubuntu 12.04 as Gateway machine.its having two interfaces eth0 with ip and eth1 connected to modem with ip address DHCP). ip-forwarding is enabled in router box. Client machine is configured as: ip address and gateway Client machines can ping router box( when pinged reply is not reaching Client machines but reply is getting in router box but not getting forwarded to client machines.Can any one please help me with this.Y reply packets are not reaching client machine (HowTos)