Access VPN modes can be either compulsory or voluntary. Because tunnels are always imposed, they are transparent to users. This solution provides consistent security. When sessions must cross several provider networks, each provider must agree to sustain VPN services, or they are lost. Cisco is working with providers to enable peering agreements that honor VPN tunnels and other attributes to provide consistent service across multiple shared networks.
Voluntary mode gives users the ability to set up VPNs at their discretion.
They have client software that initiates both the tunnel and encryption, so encapsulated traffic is invisible to the provider network. While this solution is transparent to the provider network and is one way to cross multiple provider networks, it also limits a provider's ability to offer value-added services such as priority handling. Voluntary VPNs originate at the client, which controls the connection to ensure VPN transport across multiple provider networks. Intranet and Extranet VPNs Intranet VPNs extend intranet resources and applications from a central office to employees in regional or branch offices. Extranet VPNs extend selected resources and applications to users outside a company, such as suppliers, customers, and partners.