[Openswan Users] NAT-T Does not work with Linux Kernel 2.6.18?

[Mehran Toreihi]

Dear all,
We are using Openswan 2.4.8 (KLIPS + NAT_T)
The Network topology is as follow:
192.168.0.0/24---------left_vpn(10.0.0.0/8)---------NATRouter---------Router---------NAT
Router--------right_vpn(
20.0.0.0/8)-------200.0.0.0/24
Using Redhat Linux 9.0 (Kernel 2.4.20) our configuration worked correctly as
expected and the two networks (192 and 200) could ping each other, but using
CentOS-5.2 (Kernel 2.6.18) with the same configuration, the tunnel
establishes but no ping. The packet reaches the other network. tcpdump on
the middle router shows udp nat-t encapsulation(ESP) going to the other end
but no reply. The other vpn does not do anything with the packet. Any
solutions appreciated. There is no firewall on any system or between. Any
help would be appreciated.
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