NAT

Command

NAT -- Network Address Translation commands.

Synopsis

NAT ADD STATIC <local>[:port] <global>[:port] [tcp | udp | mask]
NAT ADD OVERLOAD <local> <global> <subnet_mask>
NAT DROP <local>[:port] [tcp | udp]
NAT LIST

Description

The NAT commands control Network Address Translation, i.e. the process whereby the IP addresses contained in datagrams are manipulated to allow hosts on one network to communicate with hosts on a different network.

For example, hosts on a private intranet using unregistered 192.168.0.x addresses cannot communicate with hosts on the wider Internet because no-one would know where to route the return datagrams. NAT basically translates the unregistered addresses into registered ones and vice versa.

PAT (Port Address Translation) manipulates TCP and UDP service port numbers, for example to allow several hosts to share one IP address. The NAT commands are also used to configure PAT.

Options

NAT ADD adds an entry to the NAT table. There are two forms: STATIC and OVERLOAD.

STATIC is used to add static NAT and PAT entries, i.e. those where there is a one-to-one mapping between private and public IP addresses.
OVERLOAD is used only for dynamic PAT, where several hosts share one public IP address.

NAT DROP removes an entry from the NAT table.

NAT LIST lists the NAT table entries.

The arguments for NAT commands are as follows:

        <local>          Local private (unregistered) IP address.
        <global>         Globally recognised IP address.
        <port>           TCP or UDP service port number.
        <subnet_mask>    Bit pattern used for matching addresses.
                         e.g. 255.255.255.0

Examples

NAT ADD STATIC 192.168.0.2:87 44.131.91.2:23 tcp
NAT ADD OVERLOAD 192.168.0.0 44.131.91.3 255.255.255.240
NAT DROP 192.168.0.5:23 tcp

Files

The NAT ADD commands are usually used in IPROUTE.SYS, but may also be used in BOOTCMDS.SYS and at the command prompt.

Availability

Sysop-only.

See also

For more information about NAT please see the NAT section in the full manual.