NG_NAT(4) FreeBSD Kernel Interfaces Manual NG_NAT(4)
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
#define NG_NAT_UNREGISTERED_CGN 0x100
The corresponding libalias flags can be found by replacing the
NG_NAT prefix with PKT_ALIAS.
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>
FreeBSD 13.1-RELEASE-p6 January 24, 2021 FreeBSD 13.1-RELEASE-p6
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