Technical data

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NAT (Network Address Translation)
The router supports classic NAT (one NAT IP address assigned to one PC IP address) and a NAT technique
known as masquerading (one single NAT IP address assigned to many PC IP addresses).
General NAT Rules
1. IP Routing must be enabled.
2. NAT can be run on a per-remote-router basis.
3. Any number of PCs on the LAN may be going to the same or different remote routers at the same time. In
reality, the number of PCs on the LAN that can be supported is limited by how much memory the router
consumes maintaining table information -AND- by how many connections are currently active.
4. Some operations will NOT work. Specifically, services that place IP address/port information in the data
MAY NOT WORK until the router examines their packets and figures out what information in the data needs
to be changed. Remember that the router is remapping both IP addresses and ports.
5. When using NAT with a remote router, either the remote ISP MUST supply the IP address for NAT
translation -or- the user MUST configure the IP address for NAT translation locally.
6. Any number of PCs on the LAN may have a connection to the same or different remote routers at the same
time. In reality, the number of PCs on the LAN that can be supported is limited by the amount of memory
consumed by the router to maintain table information -AND- by the number of connections the router
“thinks” are currently active. Theoretically, up to 64,000 active connections per protocol type - TCP/UDP -
can be concurrently running, if the table space is available.
Masquerading (one single NAT IP address shared by many PC IP
addresses)
With this form of NAT, multiple local (PC) IP addresses are mapped to a single global IP address. Many local
(PCs) IP addresses are therefore hidden behind a single global IP address. The advantage of this type of NAT is
that users only need one global IP address, but the entire local LAN can still access the Internet. This NAT
technique requires not only remapping IP addresses but also TCP and UDP ports.
Each PC on the LAN side has an IP address and mask. When the router connects to an ISP, the router appears to
be a HOST with one IP address and mask. The IP address that the router uses to communicate with the ISP is
obtained dynamically (with PPP/IPCP or DHCP) or is statically configured. When the PC connects to the ISP, the
IP address and Port used by the PC are remapped to the IP address assigned to the router. This remapping is done
dynamically.