Product specifications

Efficient Networks
®
Router family
Technical Reference Guide
Chapter 4: System Management
Efficient Networks
®
Page 4-17
Network Address Translation (NAT)
Network Address Translation (NAT) allows devices on the LAN to use private IP
addresses that aren’t recognized on the Internet. The router supports the following
NAT techniques:
NOTE:
Some applications that use IP or UDP protocols may have problems with Network
Address Translation. You may be able to avoid this problem by running in TCP mode
or by disabling NAT and running as a subnetwork to your ISP.
Supported applications include AOL chat, CUSeeMe, Doom, FTP, L2TP, HTTP, Kali
Netbios over IP, NetMeeting, PCanywhere, Quake, Quicktime Video, Real Audio,
RTSP, SGI Media Base, SMTP, StreamWorks, Telnet, TFTP, Unix commands (finger,
rcp, rshell, rlogin, whois) and VDO. To read more, see “NetMeeting (H.323) with NAT”
on page 4-27.
General NAT Rules
• IP routing must be enabled.
• NAT can be run globally or on a per-remote-router and per-Ethernet-interface
basis.
• Some operations will not work. Specifically, services that place IP address/
port information in the data may not work until the router examines their
packets and figures out what information in the data needs to be changed.
Remember that the router is remapping both IP addresses and ports.
• When using NAT with a remote router, either the remote ISP must supply the
IP address for NAT translation or the user must configure the IP address for
NAT translation locally.
• Any number of PCs on the LAN may have a connection to the same or
different remote routers at the same time. In reality, the number of PCs on
the LAN that can be supported is limited by the amount of memory
consumed by the router to maintain table information and by the number of
connections the router “thinks” are currently active. Theoretically, up to
64,000 active connections per protocol type—TCP/UDP—can be
concurrently running, if the table space is available.
Masquerading: One NAT IP address is assigned to many PC IP addresses.
Classic NAT: One NAT IP address is assigned to one PC IP address.
Selective NAT: Specified IP address is assigned based on packet destination.