I would like to make both Network A and B have the same subnet. I did a changes to my config pls correct if this will work.
 
#Network A
/sbin/echo 1 > /proc/sys/net/ipv4/ip_forward
/sbin/ipchains -A forward -s 192.168.1.0/24 -j MASQ
#/sbin/ipchains -A forward -s 192.168.2.0/24 -j MASQ   # this will be omitted
/sbin/insmod ip_gre

/sbin/ip tunnel add alas mode gre remote x.x.x.x local y.y.y.y ttl 255
/sbin/ip link set netb up
/sbin/ip addr add 192.168.1.1 dev netb
/sbin/ip route add 192.168.1.0/24 dev netb   # this option dont work coz theres an existing route in routing table and the routing table is set to eth1 interface. so if i force                                                                        to add it using "route add -net 192.168.1.0  netmask 255.255.255.0 dev neta"
                                                                  it cant ping the internal ip's only the tunnel is working :(
 
 
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#Network B
/sbin/echo 1 > /proc/sys/net/ipv4/ip_forward
#/sbin/ipchains -A forward -s 192.168.2.0/24 -j MASQ  # this will be omitted
/sbin/ipchains -A forward -s 192.168.1.0/24 -j MASQ
 
/sbin/insmod ip_gre
/sbin/ip tunnel add text mode gre remote y.y.y.y local x.x.x.x ttl 255
/sbin/ip link set neta up
/sbin/ip addr add 192.168.1.2 dev neta
/sbin/ip route add 192.168.1.0/24 dev neta    # this option dont work coz theres an existing route in routing table and the routing table is set to eth1 interface. so if i force                                                                     to add it using "route add -net 192.168.1.0  netmask 255.255.255.0 dev neta"
                                                                  it cant ping the internal ip's only the tunnel is working :(
 
Pls check correct this config if its possible to work. Thanks