Implementing Site-to-Site IPSec Between a Cisco Router and Linux FreeS/WAN

It has been estimated that 80% of all Internet traffic passes through a Cisco router in reaching its ultimate destination.1 For small-to-medium sized B2B intranets and extranets that are geographically dispersed, the FreeS/WAN IPSec implementation, running on the Linux operating system, offers a secure, cost-effective, robust, and high performance open source solution to successfully interface with this large existing Cisco population. This paper begins by providing a brief overview of IPSec. It then discusses the major features, differences, and issues surrounding Cisco's IOS IPSec offering versus the FreeS/WAN offering. Finally, it describes an example implementation and step-by-step procedure that can be used to set up an IPSec site-to-site VPN between a Cisco 2621 IPSec-enabled router and an Intel Architecture-based computer running Linux with the FreeS/WAN 1.9 IPSec implementation.

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