Billion BiPAC-5112S Router Manual PDF (Setup & Configuration Guide)

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WAN.

7.1.2 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. With no servers defined,

your BIPAC-5100/5100W 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).

7.1.3 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 BIPAC-5100/5100W keeps track of the original addresses

and port numbers so incoming reply packets can have their original values restored. The

following figure illustrates this.

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7.1.4 NAT Application

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

LANs using IP Alias) behind the BIPAC-5100/5100W can communicate with three distinct

WAN networks. More examples follow at the end of this chapter.

7.1.5 NAT Mapping Types

NAT supports five types of IP/port mapping. They are:

1. One to One: In One-to-One mode, the BIPAC-5100/5100W maps one local IP address to

one global IP address.

2. Many to One: In Many-to-One mode, the BIPAC-5100/5100W maps multiple local IP

addresses to one global IP address. This is equivalent to SUA (for instance, PAT, port

address translation), Billion’s Single User Account feature that previous Billion routers

supported (the SUA Only option in today’s routers).

3. Many to Many Overload: In Many-to-Many Overload mode, the BIPAC-5100/5100W maps

the multiple local IP addresses to shared global IP addresses.

4. Many-to-Many No Overload: In Many-to-Many No Overload mode, the BIPAC-5100/5100W

maps each local IP address to a unique global IP address.

5. Server: This type allows you to specify inside servers of different services behind the NAT to

be accessible to the outside world.

The following table summarizes these types.

TYPE

IP MAPPING

One-to-One

ILA1

IGA1

Many-to-One (SUA/PAT)

ILA1

IGA1

ILA2

IGA1

…

Many-to-Many Overload

ILA1

IGA1

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ILA2

IGA2

ILA3

IGA1

ILA4

IGA2

…

Many-to-Many No Overload

ILA1

IGA1

ILA2

IGA2

ILA3

IGA3

…

Server

Server 1 IP

IGA1

Server 2 IP

IGA1

Server 3 IP

IGA1

7.2 SUA (Single User Account) Versus NAT

SUA (Single User Account) is a implementation of a subset of NAT that supports two types of

mapping, Many-to-One and Server. The BIPAC-5100/5100W also supports Full Feature NAT

to map multiple global IP addresses to multiple private LAN IP addresses of clients or servers

using mapping types as outlined in

7.3 SUA Server

A SUA server set is a list of inside (behind NAT on the LAN) servers, for example, web or FTP,

that you can make visible to the outside world even though SUA makes your whole inside

network appear as a single computer to the outside world.

You may enter a single port number or a range of port numbers to be forwarded, and the local

IP address of the desired server. The port number identifies a service; for example, web

service is on port 80 and FTP on port 21. In some cases, such as for unknown services or

where one server can support more than one service (for example both FTP and web service),

it might be better to specify a range of port numbers. You can allocate a server IP address that

corresponds to a port or a range of ports.

Many residential broadband ISP accounts do not allow you to run any server processes (such

as a Web or FTP server) from your location. Your ISP may periodically check for servers and

may suspend your account if it discovers any active services at your location. If you are unsure,

refer to your ISP.

Default Server IP Address

In addition to the servers for specified services, NAT supports a default server IP address. A

default server receives packets from ports that are not specified in this screen.

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7.3.1 Port Forwarding: Services and Port Numbers

A NAT server set is a list of inside (behind NAT on the LAN) servers, for example, web or FTP,

that you can make accessible to the outside world even though NAT makes your whole inside

network appear as a single machine to the outside world.

Use the SUA Server page to forward incoming service requests to the server(s) on your local

network. You may enter a single port number or a range of port numbers to be forwarded, and

the local IP address of the desired server. The port number identifies a service; for example,

web service is on port 80 and FTP on port 21. In some cases, such as for unknown services or

where one server can support more than one service (for example both FTP and web service),

it might be better to specify a range of port numbers.

In addition to the servers for specified services, NAT supports a default server. A service

request that does not have a server explicitly designated for it is forwarded to the default server.

If the default is not defined, the service request is simply discarded.

The most often used port numbers are shown in the following table. Please refer to RFC 1700

for further information about port numbers.

SERVICES

PORT NUMBER

ECHO

7

FTP (File Transfer Protocol)

21

SMTP (Simple Mail Transfer Protocol)

25

DNS (Domain Name System)

53

Finger

79

HTTP (Hyper Text Transfer protocol or WWW, Web)

80

POP3 (Post Office Protocol)

110

NNTP (Network News Transport Protocol)

119

SNMP (Simple Network Management Protocol)

161

SNMP trap

162

PPTP (Point-to-Point Tunneling Protocol)

1723

7.3.2 Configuring Servers Behind SUA (Example)

Let's say you want to assign ports 22-25 to one server, port 80 to another and assign a default

server IP address of 192.168.1.35 as shown in the next figure.

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7.4 Selecting the NAT Mode

Click NAT to open the following screen.

The following table describes the labels in this screen.

LABEL

DESCRIPTION

None

Select this radio button to disable NAT.

SUA Only

Select this radio button if you have just one public WAN IP address for your

BIPAC-5100/5100W. The BIPAC-5100/5100W uses Address Mapping Set 1 in the

NAT - Edit SUA/NAT Server Set

screen.

Edit Details

Click this link to go to the

NAT - Edit SUA/NAT Server Set

screen.

Full Feature

Select this radio button if you have multiple public WAN IP addresses for your

BIPAC-5100/5100W.

Edit Details

Click this link to go to the

NAT - Address Mapping Rules

screen.

Apply

Click

Apply

to save your configuration.

7.5 Configuring SUA Server

Click NAT, Select SUA Only and click Edit Details to open the following screen.

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