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 headers.

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)

Debian                                          November 28, 2007                                         ENC(4)