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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	      0x00000001    0x00000002     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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