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.\" $OpenBSD: nat.conf.5,v 1.6 2001/07/10 11:05:40 dhartmei Exp $
.\"
.\" Copyright (c) 2001 Ian Darwin. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. The name of the author may not be used to endorse or promote products
.\" derived from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd June 26, 2001
.Dt NAT.CONF 5
.Os
.Sh NAME
.Nm nat.conf
.Nd network address translation configuration file for packet filtering
.Sh DESCRIPTION
The rules file for network address translation specify which addresses
are to be mapped and which are to be redirected.
.Pp
.A
.Li nat
rule specifies that IP addresses are to be changed as the
packet traverses the given interface.
This technique of network address translation (NAT, also called
.Dq IP masquerading
on Linux) allows a single IP address to support a large range of machines on
an inside network.
Although in theory any IP address can be used on the inside, it is strongly
recommended that one of the address ranges defined by RFC 1918 be used.
These netblocks are:
.Bd -literal
10.0.0.0 - 10.255.255.255 (all of net 10, i.e., 10/8)
172.16.0.0 - 172.31.255.255 (i.e, 172.16/12)
192.168.0.0 - 192.168.255.255 (i.e., 192.168/16)
.Ed
.Pp
An
.Li rdr
rule specifies an incoming connection to be redirected
to another host and optionally a different port.
.Sh GRAMMAR
Syntax for filter rules in BNF:
.Bd -literal
rule = nat_rule | rdr_rule
nat_rule = "nat" "on" [ "!" ] ifname [ protospec ] "from" ipspec
"to" ipspec "->" address
rdr_rule = "rdr" "on" [ "!" ] ifname [ protospec ] "from" ipspec
"to" ipspec portspec "->" address portspec
protospec = "proto" ( number | "tcp" | "udp" | "icmp" )
ipspec = "any" | host
host = [ "!" ] address [ "/" mask-bits ]
portspec = "port" ( number | name )
.Ed
.Pp
Rules are processed in the order written.
Each rule must be on a line by itself.
Comments begin with the character `#'; empty lines are ignored.
.Pp
An
.Li ifname
is a network name such as fxp4, ne0, or ep1.
An
.Li address
is an IP address.
If specified,
.Li mask-bits
refers to the number of bits in the netmask.
The negation character,
.Sq ! ,
may be used before an
.Li ifname
or an
.Li address .
The protocol specification is optional.
If it is omitted from a
.Li nat
rule, "tcp", "udp", and "icmp" connections will be translated.
If the protocol specification omitted from an
.Li rdr
rule, only "tcp" connections will be redirected.
.Sh EXAMPLES
This example maps incoming requests on port 80 to port 8080, on
which Apache Tomcat is running (I don't run Tomcat as root, therefore it
doesn't have permission to bind to port 80).
.Bd -literal
# map tomcat on 8080 to appear to be on 80
rdr on ne3 proto tcp from any to any port 80 -> 127.0.0.1 port 8080
.Ed
.Pp
In the example below, lo0 is the system loopback; the machine translates
all packets coming from 192.168.168.0/24 to 204.92.77.111 going out any
interface except the loopback.
This has the net effect of making traffic from the 192.168.168.0/24
network appear as though it is part of the Internet routeable address
204.92.77.111 to nodes behind any interface on the router.
.Bd -literal
nat on ! lo0 from 192.168.168.0/24 to any -> 204.92.77.111
.Ed
.Pp
In the example below, fxp1 is the outside interface; the machine sits between a
fake internal 144.19.74.* network, and a routable external IP of 204.92.77.100:
.Bd -literal
nat on fxp1 from 144.19.74/24 to any -> 204.92.77.100
.Ed
.Pp
This longer example uses both a NAT and a redirection. Interface
kue0 is the outside interface, and its external address is 157.161.48.183.
.Bd -literal
# --------------------------------------------------------------------
# NAT
# --------------------------------------------------------------------
# translate outgoing packets' source addresses (any protocol)
# in my case, any address but the gateway's external address is mapped
#
nat on kue0 ! 157.161.48.183 to any -> 157.161.48.183
# --------------------------------------------------------------------
# RDR
# --------------------------------------------------------------------
# translate incoming packets' destination addresses
# as an example, redirect a TCP and UDP port to an internal machine
# NOTE: the lines below are split for readability
#
rdr on kue0 proto tcp from any to 157.161.48.183/32 port 8080 \e
-> 10.1.2.151 port 22
rdr on kue0 proto udp from any to 157.161.48.183/32 port 8080 \e
-> 10.1.2.151 port 53
.Ed
.Sh FILES
.Bl -tag -width "/etc/nat.conf" -compact
.It Pa /etc/hosts
.It Pa /etc/nat.conf
.It Pa /etc/protocols
.It Pa /etc/services
.El
.Sh SEE ALSO
.Xr pf 4 ,
.Xr hosts 5 ,
.Xr pf.conf 5 ,
.Xr protocols 5 ,
.Xr services 5 ,
.Xr pfctl 8
.Sh HISTORY
The
.Nm
file format appeared in
.Ox 3.0 .
|
