.\"	$OpenBSD: enc.4,v 1.20 2005/04/17 12:31:38 jmc Exp $
.\"
.\" Copyright (c) 1999 Angelos D. Keromytis
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.\"    must display the following acknowledgement:
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.Dd October 7, 1999
.Dt ENC 4
.Os
.Sh NAME
.Nm enc
.Nd Encapsulating Interface
.Sh SYNOPSIS
.Cd "pseudo-device enc" Op Ar count
.Sh DESCRIPTION
The
.Nm
interface is a software loopback mechanism that allows hosts or
firewalls to filter
.Xr ipsec 4
traffic using
.Xr pf 4 .
The
.Xr vpn 8
manpage shows an example of such a setup.
.Pp
The
.Nm
interface allows an administrator
to see outgoing packets before they have been processed by
.Xr ipsec 4 ,
or incoming packets after they have been similarly processed, via
.Xr tcpdump 8 .
.Pp
The
.Dq enc0
interface inherits all IPsec traffic.
Thus all IPsec traffic can be filtered based on
.Dq enc0 ,
and all IPsec traffic could be seen by invoking
.Xr tcpdump 8
on the
.Dq enc0
interface.
.Sh EXAMPLES
To see all outgoing packets before they have been processed via
.Xr ipsec 4 ,
or all incoming packets after they have been similarly processed:
.Pp
.Dl # tcpdump -i enc0
.Sh SEE ALSO
.Xr bpf 4 ,
.Xr inet 4 ,
.Xr ipsec 4 ,
.Xr netintro 4 ,
.Xr pf 4 ,
.Xr tcpdump 8 ,
.Xr vpn 8