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What NAT Does, 10.6.3 How NAT Works, Network Address Translation NAT

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Chapter 10 Network Address Translation (NAT) Note that inside/outside refers to the location of a host, while public/local refers to the IP address of a host used in a packet. Thus, an inside local address is the IP address of an inside host in a packet when the packet is still in the local network, while an inside public address is the IP address of the same inside host when the packet is on the WAN side. The following table summarizes this information. Table 26 NAT Definitions ITEM DESCRIPTION Inside This refers to the host on the LAN. Outside This refers to the host on the WAN. Local This refers to the packet address (source or destination) as the packet travels on the LAN. Public This refers to the packet address (source or destination) as the packet travels on the WAN. NAT never changes the IP address (either local or public) of an outside host. 10.6.2 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 public address) before forwarding the packet to the WAN side. When the response comes back, NAT translates the destination address (the inside public address) back to the inside local address before forwarding it to the original inside host. Note that the IP address (either local or public) of an outside host is never changed. The public 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 ZyXEL Device filters out all incoming inquiries, thus preventing intruders from probing your network. 10.6.3 How NAT Works Each packet has two addresses - a source address and a destination address. For outgoing packets, the inside local address is the source address on the LAN, and the inside public address is the source address on the WAN. For incoming packets, the inside local address is the destination address on the LAN, and the inside public address 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 ZyXEL 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. P-660R-Tx v3s User's Guide 89

Section	Page
User’s Guide	1
About This User's Guide	3
Document Conventions	5
Safety Warnings	7
Contents Overview	9
Table of Contents	11
List of Figures	19
List of Tables	23
Introduction	25
Introducing the ZyXEL Device	27
1.1 Overview	27
1.2 Ways to Manage the ZyXEL Device	27
1.3 Good Habits for Managing the ZyXEL Device	28
1.4 Applications for the ZyXEL Device	28
1.4.1 Internet Access	28
1.5 LEDs (Lights)	29
1.6 The RESET Button	30
1.6.1 Using the Reset Button	30
Introducing the Web Configurator	31
2.1 Overview	31
2.1.1 Accessing the Web Configurator	31
2.2 Web Configurator Main Screen	32
2.2.1 Navigation Panel	33
2.2.2 Main Window	34
Status	35
Device Information	37
3.1 Overview	37
3.2 The Device Info Screen	37
System Logs	39
4.1 Overview	39
4.2 The System Log Screen	39
Traffic Statistics	41
5.1 Overview	41
5.2 The Statistics Screen	41
Quick Start Wizard	43
Quick Start Wizard	45
6.1 Overview	45
6.2 Quick Start Wizard	45
Interface Setup	51
Internet Setup	53
7.1 Overview	53
7.1.1 What You Can Do in the Internet Screens	53
7.1.2 What You Need to Know About ADSL Internet Access	53
7.1.3 Before You Begin	54
7.2 The Internet Screen	55
7.2.1 Dynamic IP Address	56
7.2.2 Static IP Address	58
7.2.3 PPPoA/PPPoE	60
7.2.4 Bridge Mode	62
7.2.5 The PVCs Summary Screen	62
7.3 WAN Technical Reference	63
7.3.1 Encapsulation	63
7.3.2 Multiplexing	64
7.3.3 VPI and VCI	64
7.3.4 IP Address Assignment	64
7.3.5 Always-On Connection (PPP)	65
7.3.6 ATM QoS	65
7.3.7 ATM Traffic Classes	66
LAN Setup	67
8.1 Overview	67
8.1.1 What You Can Do in the LAN Screens	67
8.1.2 What You Need To Know About LAN	67
8.2 The LAN Screen	68
8.2.1 The DHCP IP Pool Summary Screen	70
8.3 LAN Technical Reference	71
8.3.1 LANs, WANs and the ZyXEL Device	71
8.3.2 DHCP Setup	71
8.3.3 DNS Server Addresses	72
8.3.4 LAN TCP/IP	72
8.3.5 RIP Setup	73
8.3.6 Multicast	74
Advanced Setup	75
Static Route	77
9.1 Overview	77
9.1.1 What You Can Do in the Static Route Screens	77
9.2 The Routing Table List Screen	78
9.2.1 The Static Route Screen	78
Network Address Translation (NAT)	81
10.1 Overview	81
10.1.1 What You Can Do in the NAT Screens	81
10.1.2 What You Need To Know About NAT	81
10.2 The NAT Screen	82
10.3 The DMZ Screen	83
10.4 The Virtual Server Screen	84
10.4.1 Configuring Servers Behind Port Forwarding (Example)	84
10.4.2 Configuring the Virtual Server Screen	85
10.5 The IP Address Mapping Screen	86
10.6 NAT Technical Reference	88
10.6.1 NAT Definitions	88
10.6.2 What NAT Does	89
10.6.3 How NAT Works	89
Quality of Service (QoS)	91
11.1 Overview	91
11.1.1 What You Can Do in the QoS Screens	92
11.1.2 What You Need to Know About QoS	92
11.2 The QoS Screen	93
11.2.1 The QoS Settings Summary Screen	95
11.3 QoS Technical Reference	96
11.3.1 IEEE 802.1p	96
11.3.2 IP Precedence	96
11.3.3 Automatic Priority Queue Assignment	97
ADSL	99
12.1 Overview	99
12.2 The ADSL Screen	99
Firewall	101
13.1 Overview	101
13.1.1 What You Can Do in the Firewall Screens	101
13.1.2 What You Need to Know About Firewall	101
13.2 The Firewall Screen	102
Access Management	103
Access Control	105
14.1 Access Control Overview	105
14.1.1 The Access Control Setup Screen	105
14.1.2 Access Control Interfaces	105
14.1.3 System Timeout	106
14.1.4 Configuring the Access Control Setup Screen	106
Filters	109
15.1 Overview	109
15.1.1 What You Can Do in the Filter Screens	109
15.1.2 What You Need to Know About Filtering	109
15.2 The IP/MAC Filter Screen	110
15.3 The Application Filter Screen	112
15.4 The URL Filter Screen	113
SNMP	115
16.1 Overview	115
16.1.1 Supported MIBs	116
16.2 The SNMP Screen	116
Universal Plug-and-Play (UPnP)	117
17.1 Overview	117
17.1.1 What You Can Do in the UPnP Screen	117
17.1.2 What You Need to Know About UPnP	117
17.2 The UPnP Screen	118
17.3 Installing UPnP in Windows Example	119
17.4 Using UPnP in Windows XP Example	122
Dynamic DNS Setup	129
18.1 Overview	129
18.1.1 What You Can Do in the DDNS Screen	129
18.1.2 What You Need To Know About DDNS	129
18.2 The Dynamic DNS Screen	130
CWMP	131
19.1 Overview	131
19.2 The CWMP Setup Screen	132
Maintenance	135
Administrator Settings	137
20.1 Overview	137
20.2 The Administrator Screen	137
Time Zone	139
21.1 Overview	139
21.2 The Time Zone Screen	139
Firmware	141
22.1 Overview	141
22.1.1 What You Need To Know About Firmware	141
22.1.2 Before You Begin	142
22.1.3 Firmware and Configuration Files Examples	142
22.2 The Firmware Screen	146
System Restart	149
23.1 Overview	149
23.2 The System Restart Screen	149
Diagnostic	151
24.1 Overview	151
24.2 The Diagnostic Screen	151
Troubleshooting and Product Specifications	153
Troubleshooting	155
25.1 Power, Hardware Connections, and LEDs	155
25.2 ZyXEL Device Access and Login	156
25.3 Internet Access	157
Product Specifications	159
26.1 Hardware Specifications	159
26.2 Firmware Specifications	159
26.3 Power Adaptor Specifications	162
Appendices and Index	165
Setting up Your Computer’s IP Address	167
Pop-up Windows, JavaScripts and Java Permissions	189
IP Addresses and Subnetting	197
Services	205
Legal Information	209

Match case Limit results 1 per page

Chapter 10 Network Address Translation (NAT)

P-660R-Tx v3s User’s Guide

Note that inside/outside refers to the location of a host, while public/local refers to the IP

address of a host used in a packet. Thus, an inside local address is the IP address of an inside

host in a packet when the packet is still in the local network, while an inside public address is

the IP address of the same inside host when the packet is on the WAN side. The following

table summarizes this information.

NAT never changes the IP address (either local or public) of an outside host.

10.6.2

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 public address) before forwarding

the packet to the WAN side. When the response comes back, NAT translates the destination

address (the inside public address) back to the inside local address before forwarding it to the

original inside host. Note that the IP address (either local or public) of an outside host is never

changed.

The public 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

ZyXEL Device filters out all incoming inquiries, thus preventing intruders from probing your

network.

10.6.3

How NAT Works

Each packet has two addresses – a source address and a destination address. For outgoing

packets, the inside local address is the source address on the LAN, and the inside public

address is the source address on the WAN. For incoming packets, the inside local address is

the destination address on the LAN, and the inside public address 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 ZyXEL 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.

Table 26

NAT Definitions

ITEM

DESCRIPTION

Inside

This refers to the host on the LAN.

Outside

This refers to the host on the WAN.

Local

This refers to the packet address (source or destination) as the packet travels on the

LAN.

Public

This refers to the packet address (source or destination) as the packet travels on the

WAN.