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 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
headers.
EXAMPLES
To see the packets the processed via ipsec(4), adjust the sysctl(8) vari‐
ables according to your need and run:
tcpdump -i enc0
SEE ALSOtcpdump(1), bpf(4), ipf(4), ipfw(4), ipsec(4), pf(4), tcpdump(8)BSD November 28, 2007 BSD
