Ip Tools; Address Translation; Nat, Pat, Or Super Nat - 3Com OfficeConnect Remote 812 Cli User's Manual

IP Tools

Address
Translation

NAT, PAT, or Super NAT ?

The OCR 812 CLI provides a standard set of IP utility programs including Ping,
TELNET and RLOGIN.
Public IP addresses are registered and can be used within a public network (e.g.,
the Internet). Due to the limitation of IP version 4 address space and the growth of
the Internet, public addresses are becoming more scarce. One solution to this
problem is to use private addresses on small LANs and to use Address Translation
when accessing devices on the public network. Address Translation changes an
IP frame's private address to a public address at the gateway of a public network
(i.e., the OCR 812).
Under PAT, the router maintains a table of active port numbers in order to


support simultaneous connections from different workstations on the LAN with
one public IP address. This public address is the WAN interface address of the
Remote Site profile. The WAN interface address can be statically configured or
dynamically learned (PPP).
Under NAT, the router maintains a table of active IP addresses in order to


support simultaneous connections from different workstations on the LAN with
one or more public IP addresses. For NAT, one or more public addresses are
assigned to you by your service provider. The OCR 812 uses NAT to statically or
dynamically assign public addresses to workstations on your private LAN.
Please do not use the WAN IP address as one of your NAT public addresses.
Under Super NAT, the router maintains a table of active IP addresses in order


to support simultaneous connections from different workstations on the LAN
with one or more public IP addresses. The OCR 812 uses NAT to statically or
dynamically assign public addresses to workstations on your private LAN.
Essentially, Super NAT is a combination of NAT and PAT. If NAT is configured,
NAT is used first (address assignment is static and/or dynamic). If additional
local workstations try to access the public network, PAT is then used. In this
way, Super NAT ensures that local workstations can always access the public
network.
NAT, PAT, and Super NAT can each be used to ensure optimal address translation.
Network conditions are the primary factor to be considered when determining
which address translation method should be used.
To determine which form of address translation is best for you, please observe the
following guidelines:
NAT should be used when the ISP assigns multiple public IP addresses to the


site. NAT is enabled by default, but the user can manually select and enable
NAT using CLI commands.
NAT allows the use of more IP clients than would be permitted if you were to
dynamically and statically map private IP addresses to one public address.
When NAT is enabled, a limited number of private clients may access the public
network (the number of private clients is determined by the number of
available public IP addresses.)
PAT should be used when the ISP assigns one public IP address to the site. The


user can manually select and enable PAT using CLI commands.

Address Translation

6-19