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Date:      Fri, 18 Jan 2002 00:05:31 -0500
From:      "James F. Hranicky" <jfh@cise.ufl.edu>
To:        security@freebsd.org
Subject:   IPSEC into network behind the primary router
Message-ID:  <20020118050532.ECC9A6BAA@mail.cise.ufl.edu>

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I'd like to be able to set up an IPSEC gateway into my current 
network setup without making sweeping changes to the network
topology, something like:


                                  ---------- [net 1]-|
                                  |                  |
                                  |                  |
   [internet]------[primary router] -------- [net 2]-|
                          |       |                  |
                          |       |                  |
                          |       ---------- [net 3]-|
                          |                          |
                          |                          |
                      [ipsec tunnel box]--------------


What I'm wondering is if the following is possible:


   [ipsec client]
       |                          ---------- [net 1] 1.1.1.0/24
       |                          |                 
       |                          M                 
   [internet]------[primary router] N------- [net 2] 1.1.2.0/24
                          A   B   O                 
                          |   |   |                 
                          |   |   ---------- [net 3] 1.1.3.0/24
                          |   |                     
                          |   |
                          |   |
                          |   |
                          |   |
                          X   Y
                    [ipsec tunnel/nat box]


		    A = 1.1.4.1/30
                    X = 1.1.4.2/30

		    B = 1.1.4.5/30
		    Y = 1.1.4.6/30

The scenario:

	- random ipsec client initiates an ipsec tunnel with
	  the ipsec tunnel box attached to my primary router

	- the packet hits interface X and is decrypted. The ipsec
	  server decrypts the packet and finds it's destined for 
	  [net 1] with a source of [ipsec client]. 

	- interface Y is set up nat, and the routing tables send
	  packets destined for [nets 123] out interface Y with 
	  a source of Y and packets destined for [ipsec client]
	  back out through interface X -- this way, packets
	  originally from [ipsec client] don't go out interfaces
	  [MNO] by mistake.

I suppose if this doesn't work I'm left with transport mode and a
gateway machine, or changing how I currently do routing for my site.

Any help appreciated,

----------------------------------------------------------------------
| Jim Hranicky, Senior SysAdmin                   UF/CISE Department |
| E314D CSE Building                            Phone (352) 392-1499 |
| jfh@cise.ufl.edu                      http://www.cise.ufl.edu/~jfh |
----------------------------------------------------------------------

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