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5.5.1 PPP Half Bridge
When the PPP Half Bridge is enabled the BIPAC-5100S 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-5100S ADSL Gateway.
5.5.2 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
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-5100S. 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.