3Com OfficeConnect Remote 812 manual Address Translation

Address Translation 6-19

IP Tools The OCR 812 CLI provides a standard set of IP utility programs including Ping, TELNET and RLOGIN.

Address Translation

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).

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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, or Super NAT ? 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.