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

NAME

     enc -- Encapsulating Interface

SYNOPSIS

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

	   device enc

DESCRIPTION

     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 firewalls 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 head-
     ers.

EXAMPLES

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

	   tcpdump -i enc0

SEE ALSO

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

BSD
								 November 28, 2007							       BSD