On Fri, 2012-01-27 at 15:31 +0530, Prashant Batra (prbatra) wrote:

So, it's clear that linux gateway is able to protect the data and send
to the connected gateway (ESP packets to outer IPs). And the second
gateway is responding with ESP packet which is decoded on linux gateway
and sent to the ip stack again by linux kernel (ICMP reply). But the
reply doesn't reach the host on left subnet.

Didn't somebody else have a similar problem recently? He found that it
worked using one internet provider but not another. If you're not seeing
anything received in tcpdump in the left subnet, then I would suspect
that the packet is getting lost in the WAN somewhere. What happens when
you ping in the other direction?

Andy