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Old 10-14-2009, 12:24 PM   #1
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Ip4 in IP6 encapsulator/decapsulator and raw socket

Hi all,

I try to implement an IPv4 in IPv6 encapsulator/decapsulator on my own. I know that ip4ip6 tunnel exists in Linux but I need to do it for some special features
So in order to do that, I use libipq (which is quite obsolete I know).
The principle is the following:

IPv4/IPv6                    IPv4/IPv6
Host A     --------------->  Host B
@IPv4A                       @IPv4B
@IPv6A                       @IPv6B

Host A pings host B in IPv4 (ping @IPv4B).
With libipq, I encapsulate the V4 ping in V6 which gives the following packet: [@IPv6A @IPv6B][@IPv4A @IPv4B][ICMPv4].
Host B receives the IPv4 in IPv6 ping. I decapsulate the IPv6 header with libipq. It gives me the following IPv4 echo request: [@IPv4A @IPv4B][ICMPv4].
Then with a raw socket where sin->addr is set to @IPv4B, I "send" the IPv4 echo request in order to have the right echo reply.
The kernel produces me an echo reply but it's where the problem begins. The echo reply has as source addr @IPv4B which is logical but also @IPv4B as destination address wereas I'm waiting @IPv4A to reply to the ping. I dont understand why. I think it has something to deal with the fact that the IPv4 echo reply is "generated locally" when I decaspulate the IPv6 header but I dont get it... Note also that I just decapsulate/encapsulate the header, I never manipulate src or dst address.
The problem come I think from the raw socket and the question could be:
Is it possible to generate a packet locally and to reply to another host?
I try raw socket with PF_INET (so I don't have to handle L2 layer), but also with AF_PACKET (so I fill the L2 header with the right value) but wathever I try, it is still not working...
If you have any tips for solving that, that would be great.

Thank you,



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