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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
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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
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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.
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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

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