Echelon i.LON 600 LonWorks/IP Server - Manual (Page 88)

Section 3: Appendixes
Network Address Translation (NAT)
Network Address Translation (NAT) allows multiple computers (hosts) to share one IP
address. The address is normally set up at the gateway between a private network and the
Internet; allowing the computers on the private network to share a global, ISP assigned
address. This is achieved by modifying the headers of each packet traveling through the
NAT gateway. At a minimum, an IP address in each packet header is replaced (translated).
For outbound packets (to the Internet), source addresses are translated from private to
public. For inbound packets, destination addresses are translated from public to private.
Internal
(Private)
Network
Internet
NAT
Gateway
Figure 40. NAT Networking
Simple Home Network Example
If you have a home network, and you have DSL or cable Internet access, you can setup
all of your computers to communicate on the same IP address (assigned by your ISP)
with the help of an NAT gateway.
Usually, addresses used in the private network (your home) are taken from the range of
addresses designated as “reserved” by the Internet Assigned Numbers Authority (IANA).
The subnets reserved for private use are:
10.x.x.x or 10/8 (Class A)
172.16.x.x - 172.31.x.x or 172.16/12 (Class B)
192.168.x.x or 192.168/16 (Class C)
169.254.x.x or 169.254/16 – “Auto-configuration”
Note that the reserved addresses are reusable, not globally unique and therefore not
routable on the Internet.
NAT translates the source addresses of outbound messages (sent by computers on your
home network) to a single address, making all of the computers on your home network
look like a single computer with a single IP address. When your home network receives
messages from an outside network, the NAT gateway “maps” the response to the proper
computer on your home network by changing the destination of the response to the
correct internal address. See
Figure 41 .
80 Using NAT, DNS, DHCP & DDNS with a L ON W ORKS Network