Explanation/Reference:
Section: Enterprise Network Design Explanation
Explanation:
A Generic Routing Encapsulation (GRE) tunnel through the Internet would not offer a guaranteed level of service. GRE is a tunneling protocol designed to encapsulate any Layer 3 protocol for transport through an IP network. Although a GRE tunnel can be used to connect to sites across a public network, such as the Internet, GRE does not have any inherent Quality of Service (QoS) mechanisms that can guarantee a level of service to any of the packets that flow through the tunnel. Because any traffic that flows through the Internet is delivered on a best-effort basis, WAN solutions that use the Internet, such as GRE tunnels, are better suited as backup strategies for WAN links that can guarantee a level of service.
Asynchronous Transfer Mode (ATM) and Frame Relay virtual circuits can provide a guaranteed level of service. Because ATM and Frame Relay virtual circuits pass through a network that has inherent QoS capabilities, each virtual circuit can guarantee a level of service to its endpoints. The service provider network is responsible for ensuring that the service level agreement (SLA) for each circuit is maintained at all times.
Similarly, a Multiprotocol Label Switching (MPLS) overlay virtual private network (VPN) can provide a guaranteed level of service. MPLS overlay VPNs are provided by a service provider and are established on an infrastructure that can ensure a level of service for all traffic that passes through the service provider network.
Reference:
CCDA 200-310 Official Cert Guide, Chapter 7, WAN Backup over the Internet, pp. 263-264