41

6.5 Configuring WAN Setup

To change your BIPAC-5100/5100W’s WAN remote node settings, click WAN. The screen

differs by the encapsulation.

6.5.1 PPP Half Bridge

When the PPP Half Bridge is enabled the BIPAC-5100/5100W becomes invisible. The DHCP

server will duplicate the WAN IP address from the ISP to the local client PC. Only one PC is

able to access the Internet using half bridge mode.

Half bridge mode can only be used when a single IP address has been assigned by the ISP, it

is not suitable for services that provide multiple IP addresses. Half bridge mode is used when

the use of NAT or NAPT is not desired and there is a single computer attached to the

BIPAC-5100/5100W ADSL Gateway.

6.5.2 When to use Half Bridge mode

When using a separate firewall that will be protecting the network, half bridge mode will allow

the firewall to appear on the internet using the publicly accessible IP address assigned by the

ISP. This configuration will allow the dedicated firewall to have full control of the inbound and

outbound traffic and is the intended purpose for this mode.

Some applications that embed the IP address of the computer in the data are not compatible

with NAT or NAPT and so the computer requires a real public IP address. However the number

of applications that are not compatible with NAT/NAPT are reducing as developers address the

42

issues. Before deciding to use half bridge mode please check to see if the application can be

made to work using the virtual server port forwarding feature on the BIPAC-5100/5100W.

Using NAT/NAPT is preferable as it provides the first line of defence against attack from

hackers/crackers and allows the connection of more than one computer.

The following table describes the labels in this screen.

LABEL

DESCRIPTION

43

Name

Enter the name of your Internet Service Provider, e.g., MyISP. This information is for

identification purposes only.

Mode

Select

Routing

(default) from the drop-down list box if your ISP allows multiple

computers to share an Internet account. Otherwise select

Bridge

.

Encapsulation

Select the method of encapsulation used by your ISP from the drop-down list box.

Choices vary depending on the mode you select in the

Mode

field.

If you select

Bridge

in the

Mode

field, select either

PPPoA

or

RFC 1483

.

If you select

Routing

in the

Mode

field, select

PPPoA

,

RFC 1483

,

ENET ENCAP

or

PPPoE

.

Multiplex

Select the method of multiplexing used by your ISP from the drop-down list. Choices

are

VC

or

LLC

.

Virtual Circuit ID

VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier) define a virtual circuit.

Refer to the appendix for more information.

VPI The valid range for the VPI is 0 to 255. Enter the VPI assigned to you.

VCI The valid range for the VCI is 32 to 65535 (0 to 31 is reserved for local management

of ATM traffic). Enter the VCI assigned to you.

ATM QoS Type

Select

CBR

(Continuous Bit Rate) to specify fixed (always-on) bandwidth for voice or

data traffic. Select

UBR

(Unspecified Bit Rate) for applications that are non-time

sensitive, such as e-mail. Select

VBR

(Variable Bit Rate) for bursty traffic and

bandwidth sharing with other applications.

VBR

is not available on all models.

Cell Rate

Cell rate configuration often helps eliminate traffic congestion that slows transmission

of real time data such as audio and video connections.

Peak Cell Rate Divide the DSL line rate (bps) by 424 (the size of an ATM cell) to find the Peak Cell

Rate (PCR). This is the maximum rate at which the sender can send cells. Type the

PCR here.

Sustain Cell Rate The Sustain Cell Rate (SCR) sets the average cell rate (long-term) that can be

transmitted. Type the SCR, which must be less than the PCR.

Maximum Burst

Size

Maximum Burst Size (MBS) refers to the maximum number of cells that can be sent at

the peak rate. Type the MBS, which is less than 65535.

Login Information

(PPPoA and PPPoE encapsulation only)

Service Name (PPPoE only) Type the name of your PPPoE service here.

User Name Enter the user name exactly as your ISP assigned. If assigned a name in the form

user@domain

where domain identifies a service name, then enter both components

exactly as given.

Password A static IP address is a fixed IP that your ISP gives you. A dynamic IP address is not

fixed; the ISP assigns you a different one each time you connect to the Internet. The

Single User Account feature can be used with either a dynamic or static IP address.

44

Select

Obtain an IP Address Automatically

if you have a dynamic IP address;

otherwise select

Static IP Address

and type your ISP assigned IP address in the

IP

Address

field below.

Connection

(PPPoA and

PPPoE

encapsulation only)

The schedule rule(s) have priority over your

Connection

settings.

Nailed-Up

Connection

Select

Nailed-Up Connection

when you want your connection up all the time. The

BIPAC-5100/5100W will try to bring up the connection automatically if it is

disconnected.

Connect on

Demand

Select

Connect on Demand

when you don't want the connection up all the time and

specify an idle time-out in the

Max Idle Timeout

field.

Max Idle Timeout Specify an idle time-out in the

Max Idle Timeout

field when you select

Connect on

Demand

. The default setting is 0, which means the Internet session will not timeout.

Subnet Mask

(ENET ENCAP

encapsulation only)

Enter a subnet mask in dotted decimal notation.

Refer to the

Subnetting

appendix in the to calculate a subnet mask If you are

implementing subnetting.

ENET ENCAP

Gateway (ENET

ENCAP

encapsulation only)

You must specify a gateway IP address (supplied by your ISP) when you select

ENET

ENCAP

in the

Encapsulation

field.

TCP MSS Option

(PPPoA/PPPoE,

Routing mode only)

This will increase the current MSS limit to the number specified, hence the tweak test

will report Max Packet Size as the specified number plus 40*. The catch is that every

time your PPPoE disconnects and re-connects it will revert back to MSS limit of 1400

(Max packet size of 1440) and needs to be entered after PPPoE connects again. This

function does not work before PPPoE connects.

*Referring to RFC879, the MSS value = MTU - 40, so by limiting the MSS value,

you will get limited MTU value.

Back

Click

Back

to return to the previous screen.

Apply

Click

Apply

to save the changes.

Cancel

Click

Cancel

to begin configuring this screen afresh.

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Chapter 7

Network Address Translation (NAT)

802.11b is only supported for the BIPAC-5100W

This chapter discusses how to configure NAT on the

BIPAC-5100/5100W

.

7.1 NAT Overview

NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP address of a

host in a packet, for example, the source address of an outgoing packet, used within one

network to a different IP address known within another network.

7.1.1 NAT Definitions

Inside/outside denotes where a host is located relative to the BIPAC-5100/5100W, for example,

the computers of your subscribers are the inside hosts, while the web servers on the Internet

are the outside hosts.

Global/local denotes the IP address of a host in a packet as the packet traverses a router, for

example, the local address refers to the IP address of a host when the packet is in the local

network, while the global address refers to the IP address of the host when the same packet is

traveling in the WAN side.

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

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

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

address (IGA) is the IP address of the same inside host when the packet is on the WAN side.

The following table summarizes this information.

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.

Global

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