help

[kanhu rauta]

Dear sir/madam,
>i have the following problem
--------------------------
>i have 3 system(a,b,c) connected by cross cable.thire connection is
a---->b------->c
the ip address are
system a:eth0::192.168.10.5 and 10.10.10.3
system  b:eth0::192.16810.7 and 10.10.10.7
system  b:eth1::192.168.18.7 and 10.10.10.5
system  c:eth0::192.168.18.5  and 10.10.10.5

mine objective   
===============
system b and c are shearing global ip(10.10.10.5).
server programe(tcp) is running on both system b and c
on b port::7500
on c port::5500
objective::system a request to get service from (10.10.10.5).this packet goto system b and b will check the destination ip along with the destination port ,
if port is 7500 it will accept the packet
else
b will forward to system c.
=============================

i have done
============
>enable ip_forward option in system b.
>modify the following files of kernel(system b only)
/usr/src/linux2.4.20-8/net/ipv4
ip_input.c
route.c
ip_output.c
==========================

problem faced by me
===================
if its udp packet this perfectely works.(system a can recive service from b or c depending on the port)

if its tcp packet then the problem
a sends syn-packet to b.
b checking the ip and port forwards it to c.
c sends the ack packet to b but b drops it
if i try to bipass the drop stastment by goto then system halts
=============================


any type of suggestion are invited
Regards
 kanhu.