Manpages

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.

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 {

};
/* Supported flags: */

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.

struct ng_nat_redirect_port {

};

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_LIST_REDIRECTS message.

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 {

};

Unique ID for this redirection is returned as response to this message.

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 {

};

Unique ID for this redirection is returned as response to this message.

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 automatically 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 connections are not affected).

NGM_NAT_ADD_SERVER (addserver)

Add another server to a pool. This is used to transparently offload 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 {

};

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 ng_nat_list_redirects.

struct ng_nat_listrdrs_entry {

};
struct ng_nat_list_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.

NGM_NAT_LIBALIAS_INFO (libaliasinfo)

Return internal statistics of libalias(3) instance as struct ng_nat_libalias_info.

struct ng_nat_libalias_info {

};
In case of ng_nat failed to retrieve a certain counter from its libalias instance, the corresponding field is returned as UINT32_MAX.

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 redirections. The description passed to and from node unchanged, together with ID providing a way for several entities to concurrently manipulate redirections in automated way.

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

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 [AT] FreeBSD.org>

BSD March 21, 2013 BSD