Prestige 2302 Support Notes
What is SUA? When should I use SUA?
SUA (Single User Account) is a unique feature supported by the Prestige to allow more than one person to access the Internet concurrently for the cost of a single user account.
When Prestige acting as SUA receives a packet from a local client destined for the outside Internet, it replaces the source address in the IP packet header with its own address and the source port in the TCP or UDP header with another value chosen out of a local pool. It then recomputed the appropriate header checksums and forwards the packet to the Internet as if it originated from the Prestige using the WAN IP address assigned by the ISP. When reply packets from the Internet are received by the Prestige, the original IP source address and TCP/UDP source port numbers are written back into the destination fields of the packet (since it is now moving in the opposite direction), the checksums are recomputed, and the packet is delivered to its intended destination. This is because SUA keeps a table of the IP addresses and port numbers of the local systems currently using it.
What is the difference between NAT and SUA?
NAT is a generic name defined in RFC 1631 'The IP Network Address Translator (NAT)'. SUA (Internet Single User Account) is ZyXEL's proprietary implementation and trade name for the PAT feature which is a specific type of NAT. SUA (or PAT for NAT) translates address into port mapping.
The primary motivation for RFC 1631 is that there is not enough IP address to go around. In addition, many corporations simply did not bother to obtain legal (globally unique) IP addresses for their networks and now finding themselves unable to connect to the Internet.
Basically, NAT is the process of translating one address to another. A NAT implementation can be as simple as substituting an IP address with another. This allows a network to solve the illegal address problem mentioned above without going through each and every host.
The goal of ZyXEL's SUA is to minimize the Internet access cost in a small office environment by using a single IP address to represent multiple hosts on the LAN. It does more than IP address translation, so that multiple hosts on the LAN can access the Internet at the same time.
How many network users does SUA/NAT support?
The Prestige does not limit the number of the users but the number of the sessions for Internet access. The Prestige supports 1024 sessions. You can view the current active sessions using the 'ip nat iface enif0 disp' command in SMT menu 24.8.
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All contents copyright (c) 2005 ZyXEL Communications Corporation.
