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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 IPv4 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 {
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 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 {
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.
NGM_NAT_LIBALIAS_INFO (libaliasinfo)
Return internal statistics of libalias(3) instance as struct ng_nat_libalias_info.
struct ng_nat_libalias_info {
uint32_t icmpLinkCount;
uint32_t udpLinkCount;
uint32_t tcpLinkCount;
uint32_t sctpLinkCount;
uint32_t pptpLinkCount;
uint32_t protoLinkCount;
uint32_t fragmentIdLinkCount;
uint32_t fragmentPtrLinkCount;
uint32_t sockCount;
};
In case of ng_nat failed to retrieve a certain counter from its libalias instance, the corresponding
field is returned as UINT32_MAX.
NGM_NAT_SET_DLT (setdlt)
Sets the data link type on the in and out hooks. Currently, supported types are DLT_RAW (raw IP
datagrams , no offset applied, the default) and DLT_EN10MB (Ethernet). DLT_ definitions can be found
in <net/bpf.h>. If you want to work on the ipfw(8) level you must use no additional offset by
specifying DLT_RAW. If, however, you attach ng_nat to a network interface directly and EN10MB is
specified, then the extra offset will be applied to take into account link-level header. In this
mode the ng_nat would also inspect appropriate type field in the Ethernet header and pass-through
any datagrams that are not IP packets.
NGM_NAT_GET_DLT (getdlt)
This control message returns the current data link type of the in and out hooks.
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
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
The ng_nat node can also be attached directly to the physical interface via ng_ether(4) node in the
graph. In the following example, we perform masquerading on a Ethernet interface connected to a public
network.
ifconfig igb0 inet x.y.8.35 netmask 0xfffff000
route add default x.y.0.1
/usr/sbin/ngctl -f- <<-SEQ
mkpeer igb0: nat lower in
name igb0:lower igb0_NAT
connect igb0: igb0_NAT: upper out
msg igb0_NAT: setdlt 1
msg igb0_NAT: setaliasaddr x.y.8.35
SEQ
SEE ALSO
libalias(3), ng_ipfw(4), natd(8), ngctl(8), ng_ether(8)
HISTORY
The ng_nat node type was implemented in FreeBSD 6.0.
AUTHORS
Gleb Smirnoff <glebius@FreeBSD.org>
Debian December 12, 2018 NG_NAT(4)