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Date:      Mon, 08 Apr 2002 14:43:50 -0700
From:      Lars Eggert <larse@ISI.EDU>
To:        Julian Elischer <julian@elischer.org>
Cc:        "Rogier R. Mulhuijzen" <drwilco@drwilco.net>, mgt@hytekblue.com, freebsd-net@FreeBSD.ORG
Subject:   Re: IPsec tunnel mode
Message-ID:  <3CB20F16.3000904@isi.edu>
References:  <Pine.BSF.4.21.0204081425380.52929-100000@InterJet.elischer.org>

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Julian Elischer wrote:
> Assign the required address to the netgraph interface and then 
> use the IP-over-UDP example in the netgraph examples.

Good idea. IP-over-UDP has advantages when it comes to firewall- and 
NAT-traversal. IP-over-IP has the advantage that it looks like IPsec 
tunnel mode on the wire and to the receiver, so it can interoperate.

> On Mon, 8 Apr 2002, Lars Eggert wrote:
> 
> 
>>Rogier R. Mulhuijzen wrote:
>> >> http://www.x-itec.de/projects/tuts/ipsec-howto.txt
>> >
>> > Unfortunately this howto, like any other mention of IPsec &
>> > tunneling on the net uses the gif interface. Which is IPoverIP, and
>> > this does not seem to match with  IPsec tunnel devices.
>>
>>There are no IPsec tunnel devices in KAME. IPsec defines "security
>>associations" (SAs), which are not represented as devices in the routing
>>table in KAME. Thus, you can't use routes to direct traffic into these
>>tunnel mode SAs, you need to set up your security policies with the
>>correct selectors (think firewall-like matching).
>>
>>*Many* tutorials on the net do not understand this disctinction, and
>>tell you to set up an IPIP tunnel (using a gif) and an IPsec tunnel
>>mode SA in parallel. This is a bad hack, since you (ab)use a side effect
>>of creating an IPIP tunnel device (it can be used for route entries) to
>>redirect traffic into your (separate) tunnel mode SA. Very roughly, you
>>set up the IPIP tunnel, then yank out the packets destined for it during 
>>outbound processing and force them over an IPsec tunnel mode SA.
>>
>>Use EITHER IPsec tunnel mode alone OR IPIP tunnels and IP transport
>>mode (draft-touch-ipsec-vpn). Mixing both can work in some scenarios 
>>where the dependencies between side effects are just right, but in 
>>general, it's a broken approach.
>>
>>Lars
>>-- 
>>Lars Eggert <larse@isi.edu>               Information Sciences Institute
>>http://www.isi.edu/larse/              University of Southern California
>>
> 



-- 
Lars Eggert <larse@isi.edu>               Information Sciences Institute
http://www.isi.edu/larse/              University of Southern California

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