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How NAT Works, NAT Application

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Chapter 11 Network Address Translation (NAT) 11.9.3 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 VMG 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 88 How NAT Works LAN 192.168.1.13 192.168.1.12 SA 192.168.1.10 NAT Table 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 SA IGA1 WAN Inside Local Address (ILA) 192.168.1.11 192.168.1.10 Inside Global Address (IGA) 11.9.4 NAT Application The following figure illustrates a possible NAT application, where three inside LANs (logical LANs using IP alias) behind the VMG can communicate with three distinct WAN networks. VMG3925-B10B User's Guide 166

Section	Page
VMG3925-B10B	1
Contents Overview	3
Table of Contents	5
User’s Guide	14
Introducing the VMG	15
1.1 Overview	15
1.2 Ways to Manage the VMG	15
1.3 Good Habits for Managing the VMG	15
1.4 Applications for the VMG	16
1.4.1 Internet Access	16
1.4.2 VMG’s USB Support	16
1.5 LEDs (Lights)	17
1.6 The RESET Button	19
1.7 Wireless Access	19
1.7.1 Using the Wi-Fi and WPS Buttons	19
The Web Configurator	21
2.1 Overview	21
2.1.1 Accessing the Web Configurator	21
2.2 Web Configurator Layout	23
2.2.1 Title Bar	23
2.2.2 Navigation Panel	24
Quick Start	28
3.1 Overview	28
3.2 Quick Start Setup	28
Tutorials	30
4.1 Overview	30
4.2 Setting Up an ADSL PPPoE Connection	30
4.3 Setting Up a Secure Wireless Network	33
4.3.1 Configuring the Wireless Network Settings	33
4.3.2 Using WPS	34
4.3.3 Without WPS	38
4.4 Setting Up Multiple Wireless Groups	39
4.5 Configuring Static Route for Routing to Another Network	42
4.6 Configuring QoS Queue and Class Setup	44
4.7 Access the VMG Using DDNS	48
4.7.1 Registering a DDNS Account on www.dyndns.org	48
4.7.2 Configuring DDNS on Your VMG	49
4.7.3 Testing the DDNS Setting	49
4.8 Configuring the MAC Address Filter	49
4.9 Access Your Shared Files From a Computer	50
Technical Reference	52
Network Map and Status Screens	53
5.1 Overview	53
5.2 The Network Map Screen	53
5.3 The Status Screen	54
Broadband	57
6.1 Overview	57
6.1.1 What You Can Do in this Chapter	57
6.1.2 What You Need to Know	58
6.1.3 Before You Begin	60
6.2 The Broadband Screen	61
6.2.1 Add/Edit Internet Connection	62
6.3 The 3G Backup Screen	70
6.4 The Advanced Screen	74
6.5 The 802.1x Screen	76
6.5.1 Modify 802.1X Settings	77
6.6 Technical Reference	78
Wireless	84
7.1 Overview	84
7.1.1 What You Can Do in this Chapter	84
7.1.2 What You Need to Know	84
7.2 The General Screen	85
7.2.1 No Security	87
7.2.2 Basic (WEP Encryption)	87
7.2.3 More Secure (WPA(2)-PSK)	88
7.3 The Guest / More AP Screen	89
7.3.1 Edit Guest / More AP	90
7.4 The WPS Screen	92
7.5 The WMM Screen	94
7.6 The WDS Screen	95
7.6.1 WDS Scan	96
7.7 The Others Screen	97
7.8 The Channel Status Screen	98
7.9 Technical Reference	99
7.9.1 Wireless Network Overview	99
7.9.2 Additional Wireless Terms	101
7.9.3 Wireless Security Overview	101
7.9.4 Signal Problems	103
7.9.5 BSS	104
7.9.6 MBSSID	104
7.9.7 Preamble Type	105
7.9.8 Wireless Distribution System (WDS)	105
7.9.9 WiFi Protected Setup (WPS)	105
Home Networking	113
8.1 Overview	113
8.1.1 What You Can Do in this Chapter	113
8.1.2 What You Need To Know	114
8.1.3 Before You Begin	115
8.2 The LAN Setup Screen	115
8.3 The Static DHCP Screen	119
8.4 The UPnP Screen	120
8.4.1 Turning On UPnP in Windows 7 Example	121
8.5 The Additional Subnet Screen	122
8.6 The STB Vendor ID Screen	124
8.7 The Wake on LAN Screen	124
8.8 The TFTP Server Name Screen	125
8.9 Technical Reference	125
8.9.1 LANs, WANs and the VMG	125
8.9.2 DHCP Setup	126
8.9.3 DNS Server Addresses	126
8.9.4 LAN TCP/IP	127
Routing	129
9.1 Overview	129
9.2 The Routing Screen	129
9.2.1 Add/Edit Static Route	130
9.3 The DNS Route Screen	131
9.3.1 The DNS Route Add Screen	131
9.4 The Policy Route Screen	132
9.4.1 Add/Edit Policy Route	133
9.5 RIP	134
9.5.1 The RIP Screen	134
Quality of Service (QoS)	135
10.1 Overview	135
10.1.1 What You Can Do in this Chapter	135
10.2 What You Need to Know	136
10.3 The Quality of Service General Screen	137
10.4 The Queue Setup Screen	138
10.4.1 Adding a QoS Queue	139
10.5 The Classification Setup Screen	140
10.5.1 Add/Edit QoS Class	141
10.6 The QoS Shaper Setup Screen	145
10.6.1 Add/Edit a QoS Shaper	146
10.7 The QoS Policer Setup Screen	146
10.7.1 Add/Edit a QoS Policer	147
10.8 Technical Reference	148
Network Address Translation (NAT)	153
11.1 Overview	153
11.1.1 What You Can Do in this Chapter	153
11.1.2 What You Need To Know	153
11.2 The Port Forwarding Screen	154
11.2.1 Add/Edit Port Forwarding	156
11.3 The Applications Screen	157
11.3.1 Add New Application	157
11.4 The Port Triggering Screen	158
11.4.1 Add/Edit Port Triggering Rule	160
11.5 The DMZ Screen	161
11.6 The ALG Screen	161
11.7 The Address Mapping Screen	162
11.7.1 Add/Edit Address Mapping Rule	163
11.8 The Sessions Screen	164
11.9 Technical Reference	164
11.9.1 NAT Definitions	165
11.9.2 What NAT Does	165
11.9.3 How NAT Works	166
11.9.4 NAT Application	166
Dynamic DNS Setup	169
12.1 Overview	169
12.1.1 What You Can Do in this Chapter	169
12.1.2 What You Need To Know	169
12.2 The DNS Entry Screen	170
12.2.1 Add/Edit DNS Entry	170
12.3 The Dynamic DNS Screen	171
Vlan Group	172
13.1 Overview	172
13.1.1 What You Can Do in this Chapter	172
13.2 The Vlan Group Screen	172
13.2.1 Add/Edit a VLAN Group	173
Interface Group	174
14.1 Overview	174
14.1.1 What You Can Do in this Chapter	174
14.2 The Interface Group Screen	174
14.2.1 Interface Group Configuration	175
14.2.2 Interface Grouping Criteria	177
USB Service	179
15.1 Overview	179
15.1.1 What You Can Do in this Chapter	179
15.1.2 ().What You Need To Know	179
15.1.3 Before You Begin	180
15.2 The File Sharing Screen	180
15.2.1 The Add New User Screen	181
15.3 The Media Server Screen	182
Firewall	184
16.1 Overview	184
16.1.1 What You Can Do in this Chapter	184
16.1.2 What You Need to Know	185
16.2 The Firewall Screen	185
16.3 The Protocol Screen	186
16.3.1 Add/Edit a Service	187
16.4 The Access Control Screen	188
16.4.1 Add/Edit an ACL Rule	189
16.5 The DoS Screen	190
MAC Filter	192
17.1 Overview	192
17.2 The MAC Filter Screen	192
Parental Control	194
18.1 Overview	194
18.2 The Parental Control Screen	194
18.2.1 Add/Edit a Parental Control Profile	195
Scheduler Rule	198
19.1 Overview	198
19.2 The Scheduler Rule Screen	198
19.2.1 Add/Edit a Schedule	198
Certificates	200
20.1 Overview	200
20.1.1 What You Can Do in this Chapter	200
20.2 What You Need to Know	200
20.3 The Local Certificates Screen	200
20.3.1 Create Certificate Request	201
20.3.2 Load Signed Certificate	203
20.4 The Trusted CA Screen	204
20.4.1 View Trusted CA Certificate	204
20.4.2 Import Trusted CA Certificate	205
Log	207
21.1 Overview	207
21.1.1 What You Can Do in this Chapter	207
21.1.2 What You Need To Know	207
21.2 The System Log Screen	208
21.3 The Security Log Screen	208
Traffic Status	210
22.1 Overview	210
22.1.1 What You Can Do in this Chapter	210
22.2 The WAN Status Screen	210
22.3 The LAN Status Screen	211
22.4 The NAT Status Screen	212
ARP Table	213
23.1 Overview	213
23.1.1 How ARP Works	213
23.2 ARP Table Screen	213
Routing Table	215
24.1 Overview	215
24.2 The Routing Table Screen	215
Multicast Status	217
25.1 Overview	217
25.2 The IGMP Status Screen	217
25.3 The MLD Status Screen	217
xDSL Statistics	219
26.1 The xDSL Statistics Screen	219
3G Statistics	222
27.1 Overview	222
27.2 The 3G Statistics Screen	222
System	224
28.1 Overview	224
28.2 The System Screen	224
User Account	225
29.1 Overview	225
29.2 The User Account Screen	225
29.2.1 The User Account Add/Edit Screen	225
Remote Management	227
30.1 Overview	227
30.2 The Remote MGMT Screen	227
30.3 The Trust Domain Screen	228
30.4 The Add Trust Domain Screen	228
TR-064	230
31.1 Overview	230
31.2 The TR-064 Screen	230
TR-069 Client	231
32.1 Overview	231
32.2 The TR-069 Client Screen	231
SNMP	233
33.1 Overview	233
33.2 The SNMP Screen	233
Time Settings	235
34.1 Overview	235
34.2 The Time Screen	235
E-mail Notification	237
35.1 Overview	237
35.2 The Email Notification Screen	237
35.2.1 Email Notification Edit	237
Log Setting	239
36.1 Overview	239
36.2 The Log Settings Screen	239
36.2.1 Example E-mail Log	240
Firmware Upgrade	242
37.1 Overview	242
37.2 The Firmware Screen	242
Backup Restore	245
38.1 Overview	245
38.2 The Backup Restore Screen	245
38.3 The ROM-D Screen	247
38.4 The Reboot Screen	247
Diagnostic	248
39.1 Overview	248
39.1.1 What You Can Do in this Chapter	248
39.2 What You Need to Know	248
39.3 Ping & TraceRoute & NsLookup	249
39.4 802.1ag	249
39.5 OAM Ping	250
Troubleshooting	253
40.1 Power, Hardware Connections, and LEDs	253
40.2 VMG Access and Login	254
40.3 Internet Access	256
40.4 Wireless Internet Access	257
40.5 USB Device Connection	258
40.6 UPnP	258
Appendices	260
Customer Support	261
Wireless LANs	267
IPv6	280
Services	288
Legal Information	292

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Chapter 11 Network Address Translation (NAT)

VMG3925-B10B User’s Guide

166

11.9.3

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

VMG 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 88

How NAT Works

11.9.4

NAT Application

The following figure illustrates a possible NAT application, where three inside LANs (logical LANs

using IP alias) behind the VMG can communicate with three distinct WAN networks.

192.168.1.13

192.168.1.10

192.168.1.11

192.168.1.12

192.168.1.10

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)