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Bring natd into main source tree now that the

Browse Source 
pppd/natd combination works ok.

Submitted by:	Ari Suutari <ari.suutari@ps.carel.fi>
This commit is contained in:
Brian Somers 1997-06-22 04:19:08 +00:00
parent 3c631446d3
commit 24084f9bfc
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/cvs2svn/branches/ARI/; revision=26781
15 changed files with 3968 additions and 0 deletions
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# $Id:$
PROG= natd
SRCS= natd.c icmp.c
CFLAGS+=-Wall
LDADD= -lalias
DPADD= ${LIBALIAS}
MAN8= natd.8
.include <bsd.prog.mk>

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#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <errno.h>
#include <signal.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <machine/in_cksum.h>
#include <alias.h>
#include "natd.h"
int SendNeedFragIcmp (int sock, struct ip* failedDgram, int mtu)
{
char icmpBuf[IP_MAXPACKET];
struct ip* ip;
struct icmp* icmp;
int icmpLen;
int failBytes;
int failHdrLen;
struct sockaddr_in addr;
int wrote;
struct in_addr swap;
/*
* Don't send error if packet is
* not the first fragment.
*/
if (ntohs (failedDgram->ip_off) & ~(IP_MF | IP_DF))
return 0;
/*
* Dont respond if failed datagram is ICMP.
*/
if (failedDgram->ip_p == IPPROTO_ICMP)
return 0;
/*
* Start building the message.
*/
ip = (struct ip*) icmpBuf;
icmp = (struct icmp*) (icmpBuf + sizeof (struct ip));
/*
* Complete ICMP part.
*/
icmp->icmp_type = ICMP_UNREACH;
icmp->icmp_code = ICMP_UNREACH_NEEDFRAG;
icmp->icmp_cksum = 0;
icmp->icmp_void = 0;
icmp->icmp_nextmtu = htons (mtu);
/*
* Copy header + 64 bits of original datagram.
*/
failHdrLen = (failedDgram->ip_hl << 2);
failBytes = failedDgram->ip_len - failHdrLen;
if (failBytes > 8)
failBytes = 8;
failBytes += failHdrLen;
icmpLen = ICMP_MINLEN + failBytes;
memcpy (&icmp->icmp_ip, failedDgram, failBytes);
/*
* Calculate checksum.
*/
icmp->icmp_cksum = InternetChecksum ((u_short*) icmp, icmpLen);
/*
* Add IP header using old IP header as template.
*/
memcpy (ip, failedDgram, sizeof (struct ip));
ip->ip_v = 4;
ip->ip_hl = 5;
ip->ip_len = htons (sizeof (struct ip) + icmpLen);
ip->ip_p = IPPROTO_ICMP;
ip->ip_tos = 0;
swap = ip->ip_dst;
ip->ip_dst = ip->ip_src;
ip->ip_src = swap;
PacketAliasIn ((char*) ip, IP_MAXPACKET);
addr.sin_family = AF_INET;
addr.sin_addr = ip->ip_dst;
addr.sin_port = 0;
/*
* Put packet into processing queue.
*/
wrote = sendto (sock,
icmp,
icmpLen,
0,
(struct sockaddr*) &addr,
sizeof addr);
if (wrote != icmpLen)
Warn ("Cannot send ICMP message.");
return 1;
}

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.\" manual page [] for natd 1.4
.Dd 15 April 1997
.Os FreeBSD
.Dt NATD 8
.Sh NAME
.Nm natd
.Nd
Network Address Translation Daemon
.Sh SYNOPSIS
.Nm
.Op Fl ldsmvu
.Op Fl permanent_link
.Op Fl dynamic
.Op Fl i Ar inport
.Op Fl o Ar outport
.Op Fl p Ar port
.Op Fl a Ar address
.Op Fl i Ar interface
.Op Fl f Ar configfile
.Nm
.Op Fl log
.Op Fl deny_incoming
.Op Fl use_sockets
.Op Fl same_ports
.Op Fl verbose
.Op Fl unregistered_only
.Op Fl permanent_link
.Op Fl dynamic
.Op Fl inport Ar inport
.Op Fl outport Ar outport
.Op Fl port Ar port
.Op Fl alias_address Ar address
.Op Fl interface Ar interface
.Op Fl config Ar configfile
.Sh DESCRIPTION
This program provides a Network Address Translation facility for use
with
.Xr divert 4
sockets under FreeBSD. Most of the command line options are available
in a single character short form or in a long form. Use of the long
form is encouraged as it makes things clearer to the casual observer.
.Pp
.Nm Natd
normally runs in the background as a daemon. It is passed raw IP packets
as they travel into and out of the machine, and will possibly change these
before re-injecting them back into the IP packet stream.
.Pp
.Nm Natd
changes all packets destined for another host so that their source
IP number is that of the current machine. For each packet changed
in this manner, an internal table entry is created to record this
fact. The source port number is also changed to indicate the
table entry applying to the packet. Packets that are received with
a target IP of the current host are checked against this internal
table. If an entry is found, it is used to determine the correct
target IP number and port to place in the packet.
.Pp
The following command line options are available.
.Bl -tag -width Fl
.It Fl log | l
Log various aliasing statistics and information to the file
.Pa /var/log/alias.log .
This file is truncated each time natd is started.
.It Fl deny_incoming | d
Reject packets destined for the current IP number that have no entry
in the internal translation table.
.It Fl use_sockets | s
Allocate a
.Xr socket 2
in order to establish an FTP data or IRC DCC send connection. This
option uses more system resources, but guarantees successful connections
when port numbers conflict.
.It Fl same_ports | m
Try to keep the same port number when altering outgoing packets.
With this option, protocols such as RPC will have a better chance
of working. If it is not possible to maintain the port number, it
will be silently changed as per normal.
.It Fl verbose | v
Don't call
.Xr fork 2
or
.Xr daemon 3
on startup. Instead, stay attached to the controling terminal and
display all packet alterations to the standard output. This option
should only be used for debugging purposes.
.It Fl unregistered_only | u
Only alter outgoing packets with an unregistered source address.
According to rfc 1918, unregistered source addresses are 10.0.0.0/8,
172.16.0.0/12 and 192.168.0.0/16.
.It Fl redirect_port Ar linkspec
Redirect incoming connections arriving to given port to another host and port.
Linkspec is of the form
proto targetIP:targetPORT [aliasIP:]aliasPORT [remoteIP[:remotePORT]]
where proto is either tcp or udp, targetIP is the desired target IP
number, targetPORT is the desired target PORT number, aliasPORT
is the requested PORT number and aliasIP is the aliasing address.
RemoteIP and remotePORT can be used to specify the connection
more accurately if necessary.
For example, the argument
.Ar tcp inside1:telnet 6666
means that tcp packets destined for port 6666 on this machine will
be sent to the telnet port on the inside1 machine.
.It Fl redirect_address Ar localIP publicIP
Redirect traffic for public IP address to a machine on the local
network. This function is known as "static NAT". Normally static NAT
is useful if your ISP has allocated a small block of IP addresses to you,
but it can even be used in the case of single address:
redirect_address 10.0.0.8 0.0.0.0
The above command would redirect all incoming traffic
to machine 10.0.0.8.
If several address aliases specify the same public address
as follows
redirect_address 192.168.0.2 public_addr
redirect_address 192.168.0.3 public_addr
redirect_address 192.168.0.4 public_addr
the incoming traffic will be directed to the last
translated local address (192.168.0.4), but outgoing
traffice to the first two addresses will still be aliased
to specified public address.
.It Fl permanent_link Ar linkspec
Create a permanent entry in the internal alias table. Linkspec is
of the form
proto targetIP:targetPORT sourceIP:sourcePORT aliasPORT
where proto is either tcp or udp, targetIP is the desired target IP
number, targetPORT is the desired target PORT number, sourceIP and
sourcePORT match the incoming packet, and aliasPORT is the requested
PORT number. Values of zero are considered as wildcards. For example,
the argument
.Ar tcp inside1:telnet outside1:0 6666
means that tcp packets destined for port 6666 on this machine from the
outside1 machine (any port) will be sent to the telnet port on the
inside1 machine.
New installations are encouraged to use redirect_port instead.
.It Fl dynamic
If the
.Fl n
or
.Fl interface
option is used,
.Nm natd
will monitor the routing socket for alterations to the
.Ar interface
passed. If the interfaces IP number is changed,
.Nm natd
will dynamically alter its concept of the alias address.
.It Fl i | inport Ar inport
Read from and write to
.Ar inport ,
treating all packets as packets coming into the machine.
.It Fl o | outport Ar outport
Read from and write to
.Ar outport ,
treating all packets as packets going out of the machine.
.It Fl p | port Ar port
Read from and write to
.Ar port ,
distinguishing packets as incoming our outgoing using the rules specified in
.Xr divert 4 .
If
.Ar port
is not numeric, it is searched for in the
.Pa /etc/services
database using the
.Xr getservbyname 3
function. If this flag is not specified, the divert port named natd will
be used as a default. An example entry in the
.Pa /etc/services
database would be:
natd 6668/divert # Network Address Translation socket
Refer to
.Xr services 5
for further details.
.It Fl a | alias_address Ar address
Use
.Ar address
as the alias address. If this option is not specified, the
.Fl n
or
.Fl interface
option must be used.
.It Fl n | interface Ar interface
Use
.Ar interface
to determine the alias address. If there is a possibility that the
IP number associated with
.Ar interface
may change, the
.Fl dynamic
flag should also be used. If this option is not specified, the
.Fl a
or
.Fl alias_address
flag must be used.
.It Fl f | config Ar configfile
Read configuration from
.Ar configfile .
.Ar Configfile
contains a list of options, one per line in the same form as the
long form of the above command line flags. For example, the line
alias_address 158.152.17.1
would specify an alias address of 158.152.17.1. Options that don't
take an argument are specified with an option of
.Ar yes
or
.Ar no
in the configuration file. For example, the line
log yes
is synonomous with
.Fl log .
Empty lines and lines beginning with '#' are ignored.
.El
.Sh RUNNING NATD
The following steps are necessary before attempting to run
.Nm natd :
.Bl -enum
.It
Get FreeBSD version 2.2 or higher. Versions before this do not support
.Xr divert 4
sockets.
.It
Build a custom kernel with the following options:
options IPFIREWALL
options IPDIVERT
Refer to the handbook for detailed instructions on building a custom
kernel.
.It
Ensure that your machine is acting as a gateway. This can be done by
specifying the line
gateway=YES
in
.Pa /etc/sysconfig ,
or using the command
sysctl -w net.inet.ip.forwarding=1
.It
If you wish to use the
.Fl n
or
.Fl interface
flags, make sure that your interface is already configured. If, for
example, you wish to specify tun0 as your
.Ar interface ,
and you're using
.Xr ppp 8
on that interface, you must make sure that you start
.Nm ppp
prior to starting
.Nm natd .
.It
Create an entry in
.Pa /etc/services :
natd 6668/divert # Network Address Translation socket
This gives a default for the
.Fl p
or
.Fl port
flag.
.El
.Pp
Running
.Nm natd
is fairly straight forward. The line
natd -interface ed0
should suffice in most cases (substituting the correct interface name). Once
.Nm natd
is running, you must ensure that traffic is diverted to natd:
.Bl -enum
.It
You will need to adjust the
.Pa /etc/rc.firewall
script to taste. If you're not interested in having a firewall, the
following lines will do:
/sbin/ipfw -f flush
/sbin/ipfw add divert 6668 all from any to any via ed0
/sbin/ipfw add pass all from any to any
The second line depends on your interface and assumes that you've updated
.Pa /etc/services
as above. If you specify real firewall rules, it's best to specify
line 2 at the start of the script so that
.Nm natd
sees all packets before they are dropped by the firewall. The firewall
rules will be run again on each packet after translation by
.Nm natd ,
minus any divert rules.
.It
Enable your firewall by setting
firewall=YES
in
.Pa /etc/sysconfig .
This tells the system startup scripts to run the
.Pa /etc/rc.firewall
script. If you don't wish to reboot now, just run this by hand from the
console. NEVER run this from a virtual session unless you put it into
the background. If you do, you'll lock yourself out after the flush
takes place, and execution of
.Pa /etc/rc.firewall
will stop at this point - blocking all accesses permanently. Running
the script in the background should be enough to prevent this disaster.
.El
.Sh SEE ALSO
.Xr socket 2 ,
.Xr getservbyname 2 ,
.Xr divert 4 ,
.Xr services 5 ,
.Xr ipfw 8
.Sh AUTHORS
This program is the result of the efforts of many people at different
times:
Divert sockets: Archie Cobbs <archie@whistle.com>
Packet aliasing: Charles Mott <cmott@srv.net>
IRC support & misc additions: Eivind Eklund <eivind@dimaga.com>
Natd: Ari Suutari <ari.suutari@ps.carel.fi>
Glue: Brian Somers <brian@awfulhak.org>

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5
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#define PIDFILE "/var/run/natd.pid"
extern void Quit (char* msg);
extern void Warn (char* msg);
extern int SendNeedFragIcmp (int sock, struct ip* failedDgram, int mtu);

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#
# Configuration file for natd.
#
#
# Logging to /var/log
#
log no
#
# Incoming connections.
#
deny_incoming no
#
# Use sockets to avoid port clashes.
#
use_sockets no
#
# Avoid port changes if possible. Makes rlogin work
# in most cases.
#
same_port yes
#
# Verbose mode. Enables dumping of packets and disables
# forking to background.
#
verbose no
#
# Divert port. Can be a name in /etc/services or numeric value.
#
port 32000
#
# Interface name or address being aliased. Either one,
# not both is required.
#
# alias_address 192.168.0.1
interface ep0
#
# Alias unregistered addresses or all addresses.
#
unregistered_only no
#
# Configure permanent links. If you use host names instead
# of addresses here, be sure that name server works BEFORE
# natd is up - this is usually not the case. So either use
# numeric addresses or hosts that are in /etc/hosts.
#
# Map connections coming to port 30000 to telnet in my_private_host.
# Remember to allow the connection /etc/rc.firewall also.
#permanent_link tcp my_private_host:telnet 0.0.0.0:0 30000
#
# Map connections coming from host.xyz.com to port 30001 to
# telnet in another_host.
#permanent_link tcp another_host:telnet host.xyz.com:0 30001

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#!/bin/sh
if [ $# != 1 ]
then
echo "usage: natd.test ifname"
exit 1
fi
ipfw flush
ipfw add divert 32000 ip from any to any via $1
ipfw add pass ip from any to any
./natd -port 32000 -interface $1 -verbose

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# natd.c icmp.c
natd.o: natd.c /usr/include/stdlib.h /usr/include/machine/ansi.h \
/usr/include/machine/types.h /usr/include/sys/cdefs.h \
/usr/include/stdio.h /usr/include/unistd.h /usr/include/sys/types.h \
/usr/include/machine/endian.h /usr/include/sys/unistd.h \
/usr/include/string.h /usr/include/ctype.h /usr/include/runetype.h \
/usr/include/sys/socket.h /usr/include/sys/time.h /usr/include/time.h \
/usr/include/errno.h /usr/include/signal.h /usr/include/sys/signal.h \
/usr/include/machine/signal.h /usr/include/machine/trap.h \
/usr/include/netdb.h /usr/include/netinet/in.h \
/usr/include/netinet/in_systm.h /usr/include/netinet/ip.h \
/usr/include/machine/in_cksum.h /usr/include/netinet/tcp.h \
/usr/include/sys/ioctl.h /usr/include/sys/ttycom.h \
/usr/include/sys/ioccom.h /usr/include/sys/filio.h \
/usr/include/sys/sockio.h /usr/include/net/if.h \
/usr/include/net/route.h /usr/include/net/radix.h \
/usr/include/arpa/inet.h /usr/include/syslog.h /usr/include/alias.h \
natd.h
icmp.o: icmp.c /usr/include/stdlib.h /usr/include/machine/ansi.h \
/usr/include/machine/types.h /usr/include/sys/cdefs.h \
/usr/include/stdio.h /usr/include/unistd.h /usr/include/sys/types.h \
/usr/include/machine/endian.h /usr/include/sys/unistd.h \
/usr/include/string.h /usr/include/ctype.h /usr/include/runetype.h \
/usr/include/sys/socket.h /usr/include/sys/time.h /usr/include/time.h \
/usr/include/errno.h /usr/include/signal.h /usr/include/sys/signal.h \
/usr/include/machine/signal.h /usr/include/machine/trap.h \
/usr/include/netdb.h /usr/include/netinet/in.h \
/usr/include/netinet/in_systm.h /usr/include/netinet/ip.h \
/usr/include/netinet/ip_icmp.h /usr/include/machine/in_cksum.h \
/usr/include/alias.h natd.h

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# $Id:$
PROG= natd
SRCS= natd.c icmp.c
CFLAGS+=-Wall
LDADD= -lalias
DPADD= ${LIBALIAS}
MAN8= natd.8
.include <bsd.prog.mk>

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#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <errno.h>
#include <signal.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <machine/in_cksum.h>
#include <alias.h>
#include "natd.h"
int SendNeedFragIcmp (int sock, struct ip* failedDgram, int mtu)
{
char icmpBuf[IP_MAXPACKET];
struct ip* ip;
struct icmp* icmp;
int icmpLen;
int failBytes;
int failHdrLen;
struct sockaddr_in addr;
int wrote;
struct in_addr swap;
/*
* Don't send error if packet is
* not the first fragment.
*/
if (ntohs (failedDgram->ip_off) & ~(IP_MF | IP_DF))
return 0;
/*
* Dont respond if failed datagram is ICMP.
*/
if (failedDgram->ip_p == IPPROTO_ICMP)
return 0;
/*
* Start building the message.
*/
ip = (struct ip*) icmpBuf;
icmp = (struct icmp*) (icmpBuf + sizeof (struct ip));
/*
* Complete ICMP part.
*/
icmp->icmp_type = ICMP_UNREACH;
icmp->icmp_code = ICMP_UNREACH_NEEDFRAG;
icmp->icmp_cksum = 0;
icmp->icmp_void = 0;
icmp->icmp_nextmtu = htons (mtu);
/*
* Copy header + 64 bits of original datagram.
*/
failHdrLen = (failedDgram->ip_hl << 2);
failBytes = failedDgram->ip_len - failHdrLen;
if (failBytes > 8)
failBytes = 8;
failBytes += failHdrLen;
icmpLen = ICMP_MINLEN + failBytes;
memcpy (&icmp->icmp_ip, failedDgram, failBytes);
/*
* Calculate checksum.
*/
icmp->icmp_cksum = InternetChecksum ((u_short*) icmp, icmpLen);
/*
* Add IP header using old IP header as template.
*/
memcpy (ip, failedDgram, sizeof (struct ip));
ip->ip_v = 4;
ip->ip_hl = 5;
ip->ip_len = htons (sizeof (struct ip) + icmpLen);
ip->ip_p = IPPROTO_ICMP;
ip->ip_tos = 0;
swap = ip->ip_dst;
ip->ip_dst = ip->ip_src;
ip->ip_src = swap;
PacketAliasIn ((char*) ip, IP_MAXPACKET);
addr.sin_family = AF_INET;
addr.sin_addr = ip->ip_dst;
addr.sin_port = 0;
/*
* Put packet into processing queue.
*/
wrote = sendto (sock,
icmp,
icmpLen,
0,
(struct sockaddr*) &addr,
sizeof addr);
if (wrote != icmpLen)
Warn ("Cannot send ICMP message.");
return 1;
}

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.\" manual page [] for natd 1.4
.Dd 15 April 1997
.Os FreeBSD
.Dt NATD 8
.Sh NAME
.Nm natd
.Nd
Network Address Translation Daemon
.Sh SYNOPSIS
.Nm
.Op Fl ldsmvu
.Op Fl permanent_link
.Op Fl dynamic
.Op Fl i Ar inport
.Op Fl o Ar outport
.Op Fl p Ar port
.Op Fl a Ar address
.Op Fl i Ar interface
.Op Fl f Ar configfile
.Nm
.Op Fl log
.Op Fl deny_incoming
.Op Fl use_sockets
.Op Fl same_ports
.Op Fl verbose
.Op Fl unregistered_only
.Op Fl permanent_link
.Op Fl dynamic
.Op Fl inport Ar inport
.Op Fl outport Ar outport
.Op Fl port Ar port
.Op Fl alias_address Ar address
.Op Fl interface Ar interface
.Op Fl config Ar configfile
.Sh DESCRIPTION
This program provides a Network Address Translation facility for use
with
.Xr divert 4
sockets under FreeBSD. Most of the command line options are available
in a single character short form or in a long form. Use of the long
form is encouraged as it makes things clearer to the casual observer.
.Pp
.Nm Natd
normally runs in the background as a daemon. It is passed raw IP packets
as they travel into and out of the machine, and will possibly change these
before re-injecting them back into the IP packet stream.
.Pp
.Nm Natd
changes all packets destined for another host so that their source
IP number is that of the current machine. For each packet changed
in this manner, an internal table entry is created to record this
fact. The source port number is also changed to indicate the
table entry applying to the packet. Packets that are received with
a target IP of the current host are checked against this internal
table. If an entry is found, it is used to determine the correct
target IP number and port to place in the packet.
.Pp
The following command line options are available.
.Bl -tag -width Fl
.It Fl log | l
Log various aliasing statistics and information to the file
.Pa /var/log/alias.log .
This file is truncated each time natd is started.
.It Fl deny_incoming | d
Reject packets destined for the current IP number that have no entry
in the internal translation table.
.It Fl use_sockets | s
Allocate a
.Xr socket 2
in order to establish an FTP data or IRC DCC send connection. This
option uses more system resources, but guarantees successful connections
when port numbers conflict.
.It Fl same_ports | m
Try to keep the same port number when altering outgoing packets.
With this option, protocols such as RPC will have a better chance
of working. If it is not possible to maintain the port number, it
will be silently changed as per normal.
.It Fl verbose | v
Don't call
.Xr fork 2
or
.Xr daemon 3
on startup. Instead, stay attached to the controling terminal and
display all packet alterations to the standard output. This option
should only be used for debugging purposes.
.It Fl unregistered_only | u
Only alter outgoing packets with an unregistered source address.
According to rfc 1918, unregistered source addresses are 10.0.0.0/8,
172.16.0.0/12 and 192.168.0.0/16.
.It Fl redirect_port Ar linkspec
Redirect incoming connections arriving to given port to another host and port.
Linkspec is of the form
proto targetIP:targetPORT [aliasIP:]aliasPORT [remoteIP[:remotePORT]]
where proto is either tcp or udp, targetIP is the desired target IP
number, targetPORT is the desired target PORT number, aliasPORT
is the requested PORT number and aliasIP is the aliasing address.
RemoteIP and remotePORT can be used to specify the connection
more accurately if necessary.
For example, the argument
.Ar tcp inside1:telnet 6666
means that tcp packets destined for port 6666 on this machine will
be sent to the telnet port on the inside1 machine.
.It Fl redirect_address Ar localIP publicIP
Redirect traffic for public IP address to a machine on the local
network. This function is known as "static NAT". Normally static NAT
is useful if your ISP has allocated a small block of IP addresses to you,
but it can even be used in the case of single address:
redirect_address 10.0.0.8 0.0.0.0
The above command would redirect all incoming traffic
to machine 10.0.0.8.
If several address aliases specify the same public address
as follows
redirect_address 192.168.0.2 public_addr
redirect_address 192.168.0.3 public_addr
redirect_address 192.168.0.4 public_addr
the incoming traffic will be directed to the last
translated local address (192.168.0.4), but outgoing
traffice to the first two addresses will still be aliased
to specified public address.
.It Fl permanent_link Ar linkspec
Create a permanent entry in the internal alias table. Linkspec is
of the form
proto targetIP:targetPORT sourceIP:sourcePORT aliasPORT
where proto is either tcp or udp, targetIP is the desired target IP
number, targetPORT is the desired target PORT number, sourceIP and
sourcePORT match the incoming packet, and aliasPORT is the requested
PORT number. Values of zero are considered as wildcards. For example,
the argument
.Ar tcp inside1:telnet outside1:0 6666
means that tcp packets destined for port 6666 on this machine from the
outside1 machine (any port) will be sent to the telnet port on the
inside1 machine.
New installations are encouraged to use redirect_port instead.
.It Fl dynamic
If the
.Fl n
or
.Fl interface
option is used,
.Nm natd
will monitor the routing socket for alterations to the
.Ar interface
passed. If the interfaces IP number is changed,
.Nm natd
will dynamically alter its concept of the alias address.
.It Fl i | inport Ar inport
Read from and write to
.Ar inport ,
treating all packets as packets coming into the machine.
.It Fl o | outport Ar outport
Read from and write to
.Ar outport ,
treating all packets as packets going out of the machine.
.It Fl p | port Ar port
Read from and write to
.Ar port ,
distinguishing packets as incoming our outgoing using the rules specified in
.Xr divert 4 .
If
.Ar port
is not numeric, it is searched for in the
.Pa /etc/services
database using the
.Xr getservbyname 3
function. If this flag is not specified, the divert port named natd will
be used as a default. An example entry in the
.Pa /etc/services
database would be:
natd 6668/divert # Network Address Translation socket
Refer to
.Xr services 5
for further details.
.It Fl a | alias_address Ar address
Use
.Ar address
as the alias address. If this option is not specified, the
.Fl n
or
.Fl interface
option must be used.
.It Fl n | interface Ar interface
Use
.Ar interface
to determine the alias address. If there is a possibility that the
IP number associated with
.Ar interface
may change, the
.Fl dynamic
flag should also be used. If this option is not specified, the
.Fl a
or
.Fl alias_address
flag must be used.
.It Fl f | config Ar configfile
Read configuration from
.Ar configfile .
.Ar Configfile
contains a list of options, one per line in the same form as the
long form of the above command line flags. For example, the line
alias_address 158.152.17.1
would specify an alias address of 158.152.17.1. Options that don't
take an argument are specified with an option of
.Ar yes
or
.Ar no
in the configuration file. For example, the line
log yes
is synonomous with
.Fl log .
Empty lines and lines beginning with '#' are ignored.
.El
.Sh RUNNING NATD
The following steps are necessary before attempting to run
.Nm natd :
.Bl -enum
.It
Get FreeBSD version 2.2 or higher. Versions before this do not support
.Xr divert 4
sockets.
.It
Build a custom kernel with the following options:
options IPFIREWALL
options IPDIVERT
Refer to the handbook for detailed instructions on building a custom
kernel.
.It
Ensure that your machine is acting as a gateway. This can be done by
specifying the line
gateway=YES
in
.Pa /etc/sysconfig ,
or using the command
sysctl -w net.inet.ip.forwarding=1
.It
If you wish to use the
.Fl n
or
.Fl interface
flags, make sure that your interface is already configured. If, for
example, you wish to specify tun0 as your
.Ar interface ,
and you're using
.Xr ppp 8
on that interface, you must make sure that you start
.Nm ppp
prior to starting
.Nm natd .
.It
Create an entry in
.Pa /etc/services :
natd 6668/divert # Network Address Translation socket
This gives a default for the
.Fl p
or
.Fl port
flag.
.El
.Pp
Running
.Nm natd
is fairly straight forward. The line
natd -interface ed0
should suffice in most cases (substituting the correct interface name). Once
.Nm natd
is running, you must ensure that traffic is diverted to natd:
.Bl -enum
.It
You will need to adjust the
.Pa /etc/rc.firewall
script to taste. If you're not interested in having a firewall, the
following lines will do:
/sbin/ipfw -f flush
/sbin/ipfw add divert 6668 all from any to any via ed0
/sbin/ipfw add pass all from any to any
The second line depends on your interface and assumes that you've updated
.Pa /etc/services
as above. If you specify real firewall rules, it's best to specify
line 2 at the start of the script so that
.Nm natd
sees all packets before they are dropped by the firewall. The firewall
rules will be run again on each packet after translation by
.Nm natd ,
minus any divert rules.
.It
Enable your firewall by setting
firewall=YES
in
.Pa /etc/sysconfig .
This tells the system startup scripts to run the
.Pa /etc/rc.firewall
script. If you don't wish to reboot now, just run this by hand from the
console. NEVER run this from a virtual session unless you put it into
the background. If you do, you'll lock yourself out after the flush
takes place, and execution of
.Pa /etc/rc.firewall
will stop at this point - blocking all accesses permanently. Running
the script in the background should be enough to prevent this disaster.
.El
.Sh SEE ALSO
.Xr socket 2 ,
.Xr getservbyname 2 ,
.Xr divert 4 ,
.Xr services 5 ,
.Xr ipfw 8
.Sh AUTHORS
This program is the result of the efforts of many people at different
times:
Divert sockets: Archie Cobbs <archie@whistle.com>
Packet aliasing: Charles Mott <cmott@srv.net>
IRC support & misc additions: Eivind Eklund <eivind@dimaga.com>
Natd: Ari Suutari <ari.suutari@ps.carel.fi>
Glue: Brian Somers <brian@awfulhak.org>

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#define PIDFILE "/var/run/natd.pid"
extern void Quit (char* msg);
extern void Warn (char* msg);
extern int SendNeedFragIcmp (int sock, struct ip* failedDgram, int mtu);

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#
# Configuration file for natd.
#
#
# Logging to /var/log
#
log no
#
# Incoming connections.
#
deny_incoming no
#
# Use sockets to avoid port clashes.
#
use_sockets no
#
# Avoid port changes if possible. Makes rlogin work
# in most cases.
#
same_port yes
#
# Verbose mode. Enables dumping of packets and disables
# forking to background.
#
verbose no
#
# Divert port. Can be a name in /etc/services or numeric value.
#
port 32000
#
# Interface name or address being aliased. Either one,
# not both is required.
#
# alias_address 192.168.0.1
interface ep0
#
# Alias unregistered addresses or all addresses.
#
unregistered_only no
#
# Configure permanent links. If you use host names instead
# of addresses here, be sure that name server works BEFORE
# natd is up - this is usually not the case. So either use
# numeric addresses or hosts that are in /etc/hosts.
#
# Map connections coming to port 30000 to telnet in my_private_host.
# Remember to allow the connection /etc/rc.firewall also.
#permanent_link tcp my_private_host:telnet 0.0.0.0:0 30000
#
# Map connections coming from host.xyz.com to port 30001 to
# telnet in another_host.
#permanent_link tcp another_host:telnet host.xyz.com:0 30001

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#!/bin/sh
if [ $# != 1 ]
then
echo "usage: natd.test ifname"
exit 1
fi
ipfw flush
ipfw add divert 32000 ip from any to any via $1
ipfw add pass ip from any to any
./natd -port 32000 -interface $1 -verbose