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NAME

       firehol-nat - set up NAT and port redirections

SYNOPSIS

       { nat to-destination | dnat [to] } ipaddr[:port] [rule-params]

       { nat to-source | snat [to] } ipaddr[:port] [rule-params]

       { nat redirect-to | redirect [to] } port[-range] [rule-params]

DESCRIPTION

       Destination NAT is provided by nat to-destination and its synonym dnat.

       Source NAT is provided by nat to-source and its synonym snat.

       Redirection  to  a  port  on the local host is provided by nat redirect-to and its synonym
       redirect.

       The port part of the new address is optional with SNAT and DNAT; if not specified it  will
       not be changed.

       When  you apply NAT to a packet, the Linux kernel will track the changes it makes, so that
       when it sees replies the transformation will be applied in the  opposite  direction.   For
       instance  if  you  changed  the destination port of a packet from 80 to 8080, when a reply
       comes back, its source is set as 80.  This means  the  original  sender  is  not  aware  a
       transformation is happening.

              Note

              The rule-params are used only to determine the traffic that will be matched for NAT
              in these commands, not to permit traffic to flow.

              Applying NAT does not automatically create rules to allow the traffic to pass.  You
              will  still  need  to include client or server entries in an interface or router to
              allow the traffic.

              When using dnat or redirect, the transformation is in the PREROUTING chain  of  the
              NAT  table  and  happens  before normal rules are matched, so your client or server
              rule should match the "modified" traffic.

              When using snat, the transformation is in the POSTROUTING chain of  the  NAT  table
              and  happens  after  normal rules are matched, so your client or server rule should
              match the "unmodified" traffic.

              See              the              netfilter              flow               diagram
              (http://upload.wikimedia.org/wikipedia/commons/3/37/Netfilter-packet-flow.svg)   if
              you would like to see how network packets are processed by the kernel in detail.

       The nat helper takes one of the following sub-commands:

       to-destination ipaddr[:port]
              Defines a Destination NAT (DNAT).  Commonly thought of  as  port-forwarding  (where
              packets  destined  for  the  firewall  with a given port and protocol are sent to a
              different IP address and possibly port), DNAT is much more  flexible  in  that  any
              number  of  parameters  can  be  matched  before  the  destination  information  is
              rewritten.

              ipaddr[:port] is the destination address to be set in packets matching rule-params.

              If no rules are given, all forwarded traffic will be matched.  outface  should  not
              be  used in DNAT since the information is not available at the time the decision is
              made.

              ipaddr[:port] accepts any --to-destination values that  iptables(8)  accepts.   Run
              iptables -j DNAT --help  for  more  information.   Multiple  ipaddr[:port]  may  be
              specified by separating with spaces and enclosing with quotes.

       to-source ipaddr[:port]
              Defines a Source NAT (SNAT).  SNAT is similar to masquerading but is more efficient
              for  static  IP  addresses.   You  can use it to give a public IP address to a host
              which does not have one behind the firewall.  See also firehol-masquerade(5).

              ipaddr[:port] is the source address to be set in packets matching rule-params.

              If no rules are given, all forwarded traffic will be matched.  inface should not be
              used  in  SNAT  since  the information is not available at the time the decision is
              made.

              ipaddr[:port]  accepts  any  --to-source  values  that  iptables(8)  accepts.   Run
              iptables -j SNAT --help  for  more  information.   Multiple  ipaddr[:port]  may  be
              specified by separating with spaces and enclosing with quotes.

       redirect-to port[-range]
              Redirect matching traffic to the local machine.  This is typically  useful  if  you
              want to intercept some traffic and process it on the local machine.

              port[-range]  is  the  port  range  (from-to)  or single port that packets matching
              rule-params will be redirected to.

              If no rules are given, all forwarded traffic will be matched.  outface  should  not
              be used in REDIRECT since the information is not available at the time the decision
              is made.

EXAMPLES

               # Port forwarding HTTP
               dnat to 192.0.2.2 proto tcp dport 80

               # Port forwarding HTTPS on to a different port internally
               dnat to 192.0.2.2:4443 proto tcp dport 443

               # Fix source for traffic leaving the firewall via eth0 with private address
               snat to 198.51.100.1 outface eth0 src 192.168.0.0/24

               # Transparent squid (running on the firewall) for some hosts
               redirect to 8080 inface eth0 src 198.51.100.0/24 proto tcp dport 80

               # Send to 192.0.2.1
               #  - all traffic arriving at or passing through the firewall
               nat to-destination 192.0.2.1

               # Send to 192.0.2.1
               #  - all traffic arriving at or passing through the firewall
               #  - which WAS going to 203.0.113.1
               nat to-destination 192.0.2.1 dst 203.0.113.1

               # Send to 192.0.2.1
               #  - TCP traffic arriving at or passing through the firewall
               #  - which WAS going to 203.0.113.1
               nat to-destination 192.0.2.1 proto tcp dst 203.0.113.1

               # Send to 192.0.2.1
               #  - TCP traffic arriving at or passing through the firewall
               #  - which WAS going to 203.0.113.1, port 25
               nat to-destination 192.0.2.1 proto tcp dport 25 dst 203.0.113.1

SEE ALSO

       · firehol(1) - FireHOL program

       · firehol.conf(5) - FireHOL configuration

       · firehol-interface(5) - interface definition

       · firehol-router(5) - router definition

       · firehol-params(5) - optional rule parameters

       · firehol-masquerade(5) - masquerade helper

       · FireHOL Website (http://firehol.org/)

       · FireHOL Online PDF Manual (http://firehol.org/firehol-manual.pdf)

       · FireHOL Online HTML Manual (http://firehol.org/manual)

       · NAT HOWTO (http://www.netfilter.org/documentation/HOWTO/NAT-HOWTO-6.html)

       · netfilter  flow  diagram  (http://upload.wikimedia.org/wikipedia/commons/3/37/Netfilter-
         packet-flow.svg)

AUTHORS

       FireHOL Team.