NG_NAT(4) BSD Kernel Interfaces Manual NG_NAT(4)NAMEng_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 alias‐
ing.
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.
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_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 {
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
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 {
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
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 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
ng_nat_list_redirects.
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[];
};
#define NG_NAT_REDIRPROTO_ADDR (IPPROTO_MAX + 3)
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.
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 ALSOlibalias(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⟩
BSD March 1, 2008 BSD
