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ENC(4)			 BSD Kernel Interfaces Manual			ENC(4)

     enc — Encapsulating Interface

     To compile this driver into the kernel, place the following line in your
     kernel configuration file:

	   device enc

     The enc interface is a software loopback mechanism that allows hosts or
     firewalls to filter ipsec(4) traffic using any firewall package that
     hooks in via the pfil(9) framework.

     The enc interface allows an administrator to see incoming and outgoing
     packets before and after they will be or have been processed by ipsec(4)
     via tcpdump(1).

     The “enc0” interface inherits all IPsec traffic.  Thus all IPsec traffic
     can be filtered based on “enc0”, and all IPsec traffic could be seen by
     invoking tcpdump(1) on the “enc0” interface.

     What can be seen with tcpdump(1) and what will be passed on to the fire‐
     walls via the pfil(9) framework can be independently controlled using the
     following sysctl(8) variables:

     Name			      Defaults	    Suggested
     net.enc.out.ipsec_bpf_mask	      0x00000003    0x00000001
     net.enc.out.ipsec_filter_mask    0x00000001    0x00000001
     net.enc.in.ipsec_bpf_mask	      0x00000001    0x00000002
     net.enc.in.ipsec_filter_mask     0x00000001    0x00000002

     For the incoming path a value of 0x1 means “before stripping off the
     outer header” and 0x2 means “after stripping off the outer header”.  For
     the outgoing path 0x1 means “with only the inner header” and 0x2 means
     “with outer and inner headers”.

     incoming path					    |------|
     ---- IPsec processing ---- (before) ---- (after) ----> |	   |
							    | Host |
     <--- IPsec processing ---- (after) ----- (before) ---- |	   |
     outgoing path					    |------|

     Most people will want to run with the suggested defaults for
     ipsec_filter_mask and rely on the security policy database for the outer

     To see the packets the processed via ipsec(4), adjust the sysctl(8) vari‐
     ables according to your need and run:

	   tcpdump -i enc0

     tcpdump(1), bpf(4), ipf(4), ipfw(4), ipsec(4), pf(4), tcpdump(8)

BSD			       November 28, 2007			   BSD

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