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Network Address Translation (NAT) is a standard IP service which allows for the translation of one IP address into another IP address. NAT has been enhanced to provide a set of advanced services called SuperNAT. SuperNAT includes a powerful Proxy Service, Port Address translation (sometimes called PAT) and Application Specific Gateways (ASGs) as well as other capabilities defines below.
The standard NAT service defined in RFC 1631. An Internal (non globally unique) IP address is translated into an External (Globally unique) IP address defined in a SNMP MIB table (TABLE mode). Up to 32 such entries may be defined. Air-Frame provides a number of powerful enhancements to standard NAT to create a set of services called 'SuperNAT'.
An External IP address of 0.0.0.0 is used by Air-Frame to indicate that no forwarding service for the Internal IP address is to be provided, thus barring the Host/PC from external communications.
The Air-Frame 'Thin Proxy' service allows the user to map ALL internal IP addresses (unlimited number) to a single External (Globally unique) IP address. The External IP address may be Static (Fixed) or Dynamic as required. This provides what Steam Packet Radio defines as a 'Thin Proxy'. The term 'Thin Proxy' is used to indicate that, as a consequence of using this approach, substantial increases in performance can be obtained versus the 'bloat ware' associated with many Classic (PC based) Proxies. The only loss of functionality versus a Classic Proxy is that Web Page Caching services - provided by some Classic Proxies - is not provided by the Thin Proxy. The SuperNAT service also allows a range of user defined IP address to be excluded from the NAT service.
SuperNAT allows the user to define a standard set of NAT translations (up to 32 Internal to External IP address mapping) and to designate one of the External IP addresses as a Thin Proxy address i.e. ALL other Hosts/PCs not defined in the Internal to External map will use this as the Thin Proxy IP address. This feature is particularly useful where the user has a limited range of external IP addresses available to service a large number of PCs. Some of the IP addresses can be used to provide externally visible services e.g. DNS, FTP, WEB servers or Video Conferencing locations (these are Excluded from the NAT translation). All other hosts will be mapped to a single IP address (they are included in the NAT translation). This feature can also be used to define a single static Proxy IP in a LAN to LAN proxy environment.
A standard Proxy ('Thin Proxy' or 'Classic Proxy') service handles outgoing connections very effectively. If the user wishes to provide external access for certain purposes e.g. an FTP server, diagnostic access etc. it is impossible. SuperNAT allows a Port Map (sometimes called PAT or Port Address Translation) to be defined (with up to 16 entries). The Port Map allows the user to indicate that requests for a specific Port (or Range of Ports) will be handled by (mapped to) a specific Internal IP address. Using the PORT MAP it is possible to define any range of required services that use unique port numbers e.g. an FTP server, a Web server a DNS server etc., etc. may be mapped to one or more Internal PCs. This service allows a user with only a single External IP address to provide any combination of required services.
The Thin Proxy service detects and automatically enables requests from the local network for DHCP and NETBIOS services. This feature allows you to log into and access remote NETBIOS (or WINS) networks over the Internet or to use remote DHCP servers from behind the Proxy without the need for any further configuration.
The Proxy DNS feature is used in conjunction with the Thin Proxy service. This feature will allow you to configure all your PCs with a DNS address (typically of your Router) that does not have to change if you change ISP or want to use a different DNS service. The only change you have to make in the case of a DNS change is to your router’s configuration.
The Port Map feature is context sensitive (or 'statefull'). Many applications use secondary ports in their normal operation, that is they start communication using a 'well known' port but then transfer to another port. FTP especially does this. The standard FTP 'well known' Port Number is actually only the control port used to pass information e.g. filenames, directory names etc.. When the user selects a file to transfer, a new (random) port is set up at each end to handle the actual transfer. The Air-Frame Port Map feature inspects the FTP control commands, identifies the new port being opened, and automatically maps it to the same IP as used by the FTP control port.
NAT services are defined at the 'Logical Route' level. It is possible to define any Route to use NAT services. To illustrate, assume an Intranet where WarpTwo is being used as an concentrator for a group of LAN and remote Hosts (PCs). These IP addresses communicate with each without using a NAT service (an Intranet) when external communication is required WarpTwo forwards the traffic to another LAN router. This LAN to LAN route is defined as the NAT route and uses a NAT service. There are many other network scenarios where this capability can be used to both increase efficiency and to provide flexible responses to network needs.
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