BitWise Dual-IP Technology Overview
by Kevin Hock, BitWise Client Programmer
Document Revision 1.2, April 19th, 2005

Overview

	BitWise is designed as an Internet and an Intranet messenger.  
That is to say, BitWise can be used on the Internet, or on an 
Intranet/LAN/VPN without sending your conversations and files over 
the Internet.  This gives BitWise a distinct advantage over most 
other instant messaging systems which are not able to make 
connections on an Intranet/VPN but instead continue to unnecessarily 
send data over the Internet.

What is dual about Dual-IP Technology?

	Every computer connected to a network or the Internet has a 
unique IP address, similar to how each home has a unique phone 
number.  However, when a computer is connected to a LAN, its IP 
address only needs to be unique to the LAN.  A device such as a 
router or gateway must be used to get onto the Internet to translate 
between Internet and LAN addresses.  Many networks use Network 
Address Translation, which gives non-routable LAN IP addresses such 
as 192.168.1.100.  Therefore, a computer on a LAN actually has two 
relevant IP addresses: its own non-routable IP address on the LAN, 
and the IP address of the router or gateway connecting it to the 
Internet.  The Dual-IP Technology refers to those two IP addresses 
hereinafter as the Internet IP and the LAN IP.

How does BitWise use the Dual-IP Technology?

	When you connect to any other device or machine on the Internet, 
such as a web server, a mail server, or the BitWise server, that 
server uses your Internet IP address to transmit data back to you.  
If your computer is connected directly to the Internet, then it has 
only an Internet IP address.  The BitWise server will give this 
address to your contacts so that they are able to establish a direct 
connection with you.
	If your computer is on a LAN, the BitWise server will see the 
Internet IP address of the router connecting you to the Internet.  
The BitWise server records that address as your Internet IP address 
that others on the Internet would use to connect to you.  However, 
your PC also detects its IP address and sends its perception of its 
IP to the server.  If the addresses are different, your computer is 
noted as using a LAN and your computer's IP is recorded as the LAN IP 
by the BitWise server.
	If the server has noted that you have both an Internet and a LAN 
IP address, the address it gives to each of your contacts depends on 
their Internet and LAN IP address.  If a contact has a different 
Internet IP address, meaning that they are not on your LAN, that 
contact is given your Internet IP address.  If a contact has the same 
Internet IP address as you, then that contact is on your LAN and is 
given your LAN IP address.  In either case, the correct IP address is 
given to establish a direct connection to you.  Note that the BitWise 
server does not give out your LAN IP address unless the Internet IP 
addresses match, so no one outside of your LAN will be able to 
"eavesdrop" on your LAN structure.

Does BitWise allow for VPNs that connect all locations?

	Yes, BitWise can be used over a VPN by enabling a Professional 
setting called VPN mode.  When using VPN mode, the Internet IP 
addresses are ignored, and only the LAN (VPN) addresses are used for 
establishing direct connections.  This deviates from the behavior 
described above, but provides Professional Networks with a powerful 
connection option not available in BitWise Personal.  This mode can 
be enabled or disabled anytime using Web Services by the Master 
Account.

	Consider a brief example: Office A connects to the Internet via a 
router with Internet IP 4.5.6.7, and all PCs at Office A are given 
LAN/VPN addresses of 192.168.1.x.  Office B connects to the Internet 
via a router with Internet IP 7.6.5.4, and all PCs at Office B are 
given LAN/VPN addresses of 192.168.2.x.  Without the VPN mode 
enabled, connections between offices would be routed via the Internet 
as originally described and are will not pass through the NAT router 
at each location, leading to direct connection failures.  With the 
VPN mode enabled, only the 192.168.x.x. addresses are used, and the 
direct connections will be routed through the VPN rather than over 
the Internet.

Auto-Detecting the LAN IP address and overriding the LAN IP

	BitWise detects your computer's IP address by querying your 
operating system for the IP address(es) currently assigned to the 
network interface(s) in your computer.  Most systems have only one 
network interface, so only one IP address will be returned.  On 
systems with multiple network interfaces, BitWise will display a list 
of IP addresses assigned to the computer and ask you select which one 
should be used as the BitWise LAN IP.  You can reselect the LAN IP 
address by entering the Setup prior to logging in and clicking Detect 
LAN IP.

	There may be some situations where the IP address for reaching 
your computer is the address of a router, gateway or other device.  
You can override an auto-detected IP address by entering the Setup 
prior to logging in and clicking Override LAN IP.  Enter the IP 
address in dotted decimal notation that you want BitWise to use for 
your LAN IP.  BitWise will confirm the IP address by displaying it 
back to you.  Once you confirm your entry, BitWise will use that IP 
address as your LAN IP until you override it again or use the Detect 
LAN IP feature to reselect one of the auto-detected IP addresses.