Businesses today are looking to the Internet for wide area network (WAN) solutions that in the recent past they could get only by choosing Frame Relay or T1 dedicated links. To achieve the security that is required for corporate users, virtual private networks (VPNs) can be used to guarantee that traffic is securely tunneled over the Internet. Up to now, most VPNs have been provisioned using Layer 2 technologies, such as Frame Relay and asynchronous transfer mode (ATM).

These technologies provided secure tunnels, were resistant to Denial-of-Service (DoS) and intrusion attacks, and provided address and routing separation. The problem with Layer 2 VPN technology is that it does not scale well. As the network grows, the number of required virtual circuits achieving optimal routing scales non-linearly. It is also difficult to provide traffic engineering using a Layer 2 VPN approach.

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