Echelon i.LON 600 LonWorks/IP Server - Manual (Page 89)

Section 3: Appendixes
Home Network
192.168.1.100
192.168.1.101
192.168.1.1
NAT
Gateway
LAN Side
WAN Side
131.28.203.17
ISP Internet
WAN Side Address is
Assigned by ISP
Figure 41. NAT Gateway Structure
The below steps illustrate the NAT process:
1. Using one of your home PCs, open Internet Explorer and type
www.echelon.com. Your PC will send a connection initiation (SYN flagged)
TCP packet to www.echelon.com (which it has previously resolved to an IP
address using DNS). The Ethernet frame containing the packet is addressed to
the private interface of the LAN side of the NAT gateway (your PC's default
gateway).
Headers contain:
Source IP: 192.168.1.100 (your PC)
Destination IP: 205.229.51.8 (www.echelon.com)
2. The NAT gateway receives the frame and changes the source IP addresses (and
checksums) in the packet headers (IP and TCP) from your computer's private
address to a public address and forwards the packet to the Internet.
Headers contain:
Source IP: 131.23.203.17 (example global address provided by your ISP)
Destination IP: 205.229.51.8 (www.echelon.com)
3. The Echelon Web site replies with a TCP SYN / ACK flagged packet IP
addressed to your home global address. (e.g. 131.23.203.17)
Headers contain:
Source IP: 205.229.51.8
Destination IP: 131.23.203.17
4. The NAT gateway receives this information and changes the destination IP
addresses (and checksums) to your PC's private address before sending it to your
PC.
i.LON 600 User’s Guide 81