Chapter 10 Network Address Translation (NAT)
B222s User’s Guide
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10.5.2 What NAT Does
In the simplest form, NAT changes the source IP address in a packet received from a subscriber
(the inside local address) to another (the inside global address) before forwarding the packet to the
WAN side. When the response comes back, NAT translates the destination address (the inside
global address) back to the inside local address before forwarding it to the original inside host. Note
that the IP address (either local or global) of an outside host is never changed.
The global IP addresses for the inside hosts can be either static or dynamically assigned by the ISP.
In addition, you can designate servers, for example, a web server and a Telnet server, on your local
network and make them accessible to the outside world. If you do not define any servers, NAT
offers the additional benefit of firewall protection. With no servers defined, your LTE Device filters
out all incoming inquiries, thus preventing intruders from probing your network. For more
information on IP address translation, refer to RFC 1631, The IP Network Address Translator (NAT).
10.5.3 How NAT Works
Each packet has two addresses – a source address and a destination address. For outgoing packets,
the ILA (Inside Local Address) is the source address on the LAN, and the IGA (Inside Global
Address) is the source address on the WAN. For incoming packets, the ILA is the destination
address on the LAN, and the IGA is the destination address on the WAN. NAT maps private (local)
IP addresses to globally unique ones required for communication with hosts on other networks. It
replaces the original IP source address (and TCP or UDP source port numbers for Many-to-One and
Many-to-Many Overload NAT mapping) in each packet and then forwards it to the Internet. The LTE
Device keeps track of the original addresses and port numbers so incoming reply packets can have
their original values restored. The following figure illustrates this.
Figure 57
How NAT Works
192.168.1.13
192.168.1.10
192.168.1.11
192.168.1.12
SA
192.168.1.10
SA
IGA1
Inside Local
IP Address
192.168.1.10
192.168.1.11
192.168.1.12
192.168.1.13
Inside Global
IP Address
IGA 1
IGA 2
IGA 3
IGA 4
NAT Table
WAN
LAN
Inside Local
Address (ILA)
Inside Global
Address (IGA)
Summary of Contents for B222s
Page 4: ...Contents Overview B222s User s Guide 4 ...
Page 12: ...Table of Contents B222s User s Guide 12 ...
Page 13: ...13 PART I User s Guide ...
Page 14: ...14 ...
Page 28: ...28 ...
Page 78: ...Chapter 7 Routing B222s User s Guide 78 ...
Page 82: ...Chapter 8 DNS Route B222s User s Guide 82 ...
Page 102: ...Chapter 10 Network Address Translation NAT B222s User s Guide 102 ...
Page 114: ...Chapter 12 Firewall B222s User s Guide 114 ...
Page 120: ...Chapter 14 Parental Control B222s User s Guide 120 ...
Page 125: ...Chapter 15 VoIP B222s User s Guide 125 ...
Page 144: ...Chapter 15 VoIP B222s User s Guide 144 ...
Page 154: ...Chapter 17 Traffic Status B222s User s Guide 154 ...
Page 156: ...Chapter 18 User Account B222s User s Guide 156 ...
Page 170: ...Chapter 24 Backup Restore B222s User s Guide 170 ...
Page 172: ...Chapter 25 Diagnostic B222s User s Guide 172 ...
Page 218: ...Appendix B Setting Up Your Computer s IP Address B222s User s Guide 218 ...
Page 228: ...Appendix C Pop up Windows JavaScript and Java Permissions B222s User s Guide 228 ...
Page 252: ...Appendix E Common Services B222s User s Guide 252 ...