NAME
enc —
Encapsulating Interface
SYNOPSIS
To compile this driver into the kernel, place the following line in your kernel configuration file:
device encDESCRIPTION
Theenc 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