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ENC(4)		       FreeBSD 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	traf-
     fic 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)

FreeBSD	11.1		       November	28, 2007		  FreeBSD 11.1


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