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NAME

     ng_nat - NAT netgraph node type

SYNOPSIS

     #include <netgraph/ng_nat.h>

DESCRIPTION

     An ng_nat node performs network address translation (NAT) of packets
     passing through it.  A nat node uses libalias(3) engine for packet
     aliasing.  At this moment it supports only the basic functionality of the
     library.

HOOKS

     This node type has two hooks:

     out     Packets received on this hook are considered outgoing and will be
             masqueraded to a configured address.

     in      Packets coming on this hook are considered incoming and will be
             dealiased.

CONTROL MESSAGES

     This node type supports the generic control messages, plus the following:

     NGM_NAT_SET_IPADDR (setaliasaddr)
             Configure aliasing address for a node.  After both hooks have
             been connected and aliasing address was configured, a node is
             ready for aliasing operation.

     NGM_NAT_SET_MODE (setmode)
             Set node’s operation mode using supplied struct ng_nat_mode.

             struct ng_nat_mode {
                     uint32_t        flags;
                     uint32_t        mask;
             };
             /* Supported flags: */
             #define NG_NAT_LOG                      0x01
             #define NG_NAT_DENY_INCOMING            0x02
             #define NG_NAT_SAME_PORTS               0x04
             #define NG_NAT_UNREGISTERED_ONLY        0x10
             #define NG_NAT_RESET_ON_ADDR_CHANGE     0x20
             #define NG_NAT_PROXY_ONLY               0x40
             #define NG_NAT_REVERSE                  0x80

     NGM_NAT_SET_TARGET (settarget)
             Configure target address for a node.  When an incoming packet not
             associated with any pre-existing aliasing link arrives at the
             host machine, it will be sent to the specified address.

SHUTDOWN

     This node shuts down upon receipt of a NGM_SHUTDOWN control message, or
     when both hooks are disconnected.

EXAMPLES

     In the following example, the packets are injected into a nat node using
     the ng_ipfw(4) node.

           # Create NAT node
           ngctl mkpeer ipfw: nat 60 out
           ngctl name ipfw:60 nat
           ngctl connect ipfw: nat: 61 in
           ngctl msg nat: setaliasaddr x.y.35.8

           # Divert traffic into NAT node
           ipfw add 300 netgraph 61 all from any to any in via fxp0
           ipfw add 400 netgraph 60 all from any to any out via fxp0

           # Let packets continue with after being (de)aliased
           sysctl net.inet.ip.fw.one_pass=0

     The ng_nat node can be inserted right after the ng_iface(4) node in the
     graph.  In the following example, we perform masquerading on a serial
     line with HDLC encapsulation.

           /usr/sbin/ngctl -f- <<-SEQ
                   mkpeer cp0: cisco rawdata downstream
                   name cp0:rawdata hdlc
                   mkpeer hdlc: nat inet in
                   name hdlc:inet nat
                   mkpeer nat: iface out inet
                   msg nat: setaliasaddr x.y.8.35
           SEQ
           ifconfig ng0 x.y.8.35 x.y.8.1

SEE ALSO

     libalias(3), ng_ipfw(4), natd(8), ngctl(8)

HISTORY

     The ng_nat node type was implemented in FreeBSD 6.0.

AUTHORS

     Gleb Smirnoff 〈glebius@FreeBSD.org