ZyXEL Communications P-334WT Support Notes page 5

source address and TCP/UDP source port numbers are written 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 true destination. This is because SUA keeps a table of the IP addresses and port numbers
of the local systems currently using it.
11. 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 implementation and trade name for functioning PAT
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 a 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 rectify the illegal address
problem mentioned above without going through each and every host.
The design 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 the multiple hosts inside. It does more than IP address
translation, so that multiple hosts on the LAN can access the Internet at the same time.
12. How many network users can the SUA/NAT support?
The Prestige does not limit the number of the users but the number of the sessions. The Prestige 334WT
supports 2048 sessions that you can use the 'ip nat iface enif1' command in menu 24.8 to view the
current active sessions.
13. What are Device filters and Protocol filters?
In ZyNOS, the filters have been separated into two groups. One group is called 'device filter group', and
the other is called 'protocol filter group'. Generic filters belong to the 'device filter group', TCP/IP and
IPX filters belong to the 'protocol filter group'.
14. Why can't I configure device filters or protocol filters?
In ZyNOS, you can not mix different filter groups in the same filter set.
15. How can I protect against IP spoofing attacks?
The P-334WT's firewall will automatically detect the IP spoofing and drop it if the firewall is turned on.