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NG_NAT(4)		 BSD Kernel Interfaces Manual		     NG_NAT(4)

     ng_nat — NAT netgraph node type

     #include <netgraph/ng_nat.h>

     An ng_nat node performs network address translation (NAT) of packets
     passing through it.  A nat node uses libalias(3) engine for packet alias‐

     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

     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.

     NGM_NAT_REDIRECT_PORT (redirectport)
	     Redirect incoming connections arriving to given port(s) to
	     another host and port(s).	The following struct
	     ng_nat_redirect_port must be supplied as argument.

	     #define NG_NAT_DESC_LENGTH	     64
	     struct ng_nat_redirect_port {
		     struct in_addr  local_addr;
		     struct in_addr  alias_addr;
		     struct in_addr  remote_addr;
		     uint16_t	     local_port;
		     uint16_t	     alias_port;
		     uint16_t	     remote_port;
		     uint8_t	     proto;
		     char	     description[NG_NAT_DESC_LENGTH];

	     Redirection is assigned an unique ID which is returned as
	     response to this message, and information about redirection added
	     to list of static redirects which later can be retrieved by

     NGM_NAT_REDIRECT_ADDR (redirectaddr)
	     Redirect traffic for public IP address to a machine on the local
	     network.  This function is known as static NAT.  The following
	     struct ng_nat_redirect_addr must be supplied as argument.

	     struct ng_nat_redirect_addr {
		     struct in_addr  local_addr;
		     struct in_addr  alias_addr;
		     char	     description[NG_NAT_DESC_LENGTH];

	     Unique ID for this redirection is returned as response to this

     NGM_NAT_REDIRECT_PROTO (redirectproto)
	     Redirect incoming IP packets of protocol proto (see protocols(5))
	     to a machine on the local network.	 The following struct
	     ng_nat_redirect_proto must be supplied as argument.

	     struct ng_nat_redirect_proto {
		     struct in_addr  local_addr;
		     struct in_addr  alias_addr;
		     struct in_addr  remote_addr;
		     uint8_t	     proto;
		     char	     description[NG_NAT_DESC_LENGTH];

	     Unique ID for this redirection is returned as response to this

     NGM_NAT_REDIRECT_DYNAMIC (redirectdynamic)
	     Mark redirection with specified ID as dynamic, i.e., it will
	     serve for exactly one next connection and then will be automati‐
	     cally deleted from internal links table.  Only fully specified
	     links can be made dynamic.	 The redirection with this ID is also
	     immediately deleted from user-visible list of static redirects
	     (available through NGM_NAT_LIST_REDIRECTS message).

     NGM_NAT_REDIRECT_DELETE (redirectdelete)
	     Delete redirection with specified ID (currently active connec‐
	     tions are not affected).

     NGM_NAT_ADD_SERVER (addserver)
	     Add another server to a pool.  This is used to transparently off‐
	     load network load on a single server and distribute the load
	     across a pool of servers, also known as LSNAT (RFC 2391).	The
	     following struct ng_nat_add_server must be supplied as argument.

	     struct ng_nat_add_server {
		     uint32_t	     id;
		     struct in_addr  addr;
		     uint16_t	     port;

	     First, the redirection is set up by NGM_NAT_REDIRECT_PORT or
	     NGM_NAT_REDIRECT_ADDR.  Then, ID of that redirection is used in
	     multiple NGM_NAT_ADD_SERVER messages to add necessary number of
	     servers.  For redirections created by NGM_NAT_REDIRECT_ADDR, the
	     port is ignored and could have any value.	Original redirection's
	     parameters local_addr and local_port are also ignored after
	     NGM_NAT_ADD_SERVER was used (they are effectively replaced by
	     server pool).

     NGM_NAT_LIST_REDIRECTS (listredirects)
	     Return list of configured static redirects as struct

	     struct ng_nat_listrdrs_entry {
		     uint32_t	     id;	     /* Anything except zero */
		     struct in_addr  local_addr;
		     struct in_addr  alias_addr;
		     struct in_addr  remote_addr;
		     uint16_t	     local_port;
		     uint16_t	     alias_port;
		     uint16_t	     remote_port;
		     uint16_t	     proto;	     /* Valid proto or NG_NAT_REDIRPROTO_ADDR */
		     uint16_t	     lsnat;	     /* LSNAT servers count */
		     char	     description[NG_NAT_DESC_LENGTH];
	     struct ng_nat_list_redirects {
		     uint32_t		     total_count;
		     struct ng_nat_listrdrs_entry redirects[];

	     Entries of the redirects array returned in the unified format for
	     all redirect types.  Ports are meaningful only if protocol is
	     either TCP or UDP and static NAT redirection (created by
	     NGM_NAT_REDIRECT_ADDR) is indicated by proto set to
	     NG_NAT_REDIRPROTO_ADDR.  If lsnat servers counter is greater than
	     zero, then local_addr and local_port are also meaningless.

     NGM_NAT_PROXY_RULE (proxyrule)
	     Specify a transparent proxying rule (string must be supplied as
	     argument).	 See libalias(3) for details.

     In all redirection messages local_addr and local_port mean address and
     port of target machine in the internal network, respectively.  If
     alias_addr is zero, then default aliasing address (set by
     NGM_NAT_SET_IPADDR) is used.  Connections can also be restricted to be
     accepted only from specific external machines by using non-zero
     remote_addr and/or remote_port.  Each redirection assigned an ID which
     can be later used for redirection manipulation on individual basis (e.g.,
     removal).	This ID guaranteed to be unique until the node shuts down (it
     will not be reused after deletion), and is returned to user after making
     each new redirection or can be found in the stored list of all redirec‐
     tions.  The description passed to and from node unchanged, together with
     ID providing a way for several entities to concurrently manipulate redi‐
     rections in automated way.

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

     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
	   ifconfig ng0 x.y.8.35 x.y.8.1

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

     The ng_nat node type was implemented in FreeBSD 6.0.

     Gleb Smirnoff ⟨⟩

BSD				 March 1, 2008				   BSD

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