TechNote: VPN Configuration Case Studies
1-8 VPN Concepts, Tips, and Techniques
Version 1.0, July 2003
It is also important to make sure the addresses do not overlap or conflict. That is, each set of
addresses should be separate and distinct.
It will also be important to know the subnet mask of both gateway LAN Connections. Use the
worksheet in Appendix A to gather the necessary address and subnet mask information to aid in
the configuration and troubleshooting process.
Firewalls
It is important to understand that many gateways are also firewalls. VPN tunnels cannot function
properly if firewall settings disallow all incoming traffic. Please refer to the firewall instructions
for both gateways to understand how to open specific protocols, ports, and addresses that you
intend to allow.
Setting Up a VPN Tunnel Between Gateways
A SA, frequently called a tunnel, is the set of information that allows two entities (networks, PCs,
routers, firewalls, gateways) to “trust each other” and communicate securely as they pass
information over the Internet.
Table 1-1. WAN (Internet/Public) and LAN (Internal/Private) Addressing
Gateway LAN or WAN VPNC Example Address
Gateway A LAN (Private) 10.5.6.1
Gateway A WAN (Public) 14.15.16.17
Gateway B LAN (Private) 22.23.24.25
Gateway B WAN (Public) 172.23.9.1
Table 1-2. Subnet Addressing
Gateway LAN or WAN Interface Name Example Subnet Mask
Gateway A LAN (Private) Subnet Mask A 255.255.255.0
Gateway B LAN (Private) Subnet Mask B 255.255.255.0
Intro2VPN.fm Page 8 Sunday, November 23, 2003 12:57 PM
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