Which three Layer 3 VPN technologies are based on the overlay model? (Choose three.)

A.
ATM virtual circuits

B.
Frame Relay virtual circuits

C.
GRE/IPsec

D.
L2TPv3

E.
MPLS Layer 3 VPNs

F.
DMVPNs

Explanation:

The overlay model, where the service provider provides emulated leased lines to the customer.
The service provider provides the customer with a set of emulated leased lines. These leased
lines are calledVCs, which can be either constantly available (PVCs) or established on demand
(SVCs). The QoSguarantees in the overlay VPN model usually are expressed in terms of
bandwidth guaranteed on a certain VC(Committed Information Rate or CIR) and maximum
bandwidth available on a certain VC (Peak InformationRate or PIR). The committed bandwidth
guarantee usually is provided through the statistical nature of theLayer 2 service but depends on
the overbooking strategy of the service providerThe peer-to-peer model, where the service
provider and the customer exchange Layer 3 routing informationand the provider relays the data
between the customer sites on the optimum path between the sites andwithout the customer’s
involvement.
The peer-to-peer VPN model was introduced a few years ago to alleviate the drawbacks of the
overlay VPNmodel. In the peer-to-peer model, the Provider Edge (PE) device is a router (PErouter) that directly exchangesrouting information with the CPE router. The Managed Network
service offered by many service providers,where the service provider also manages the CPE
devices, is not relevant to this discussion because it’s only arepackaging of another service. The
Managed Network provider concurrently assumes the role of the VPNservice provider providing
the VPN infrastructure) and part of the VPN customer role (managing the CPEdevice).
The peer-to-peer model provides a number of advantages over the traditional overlay model:
Routing (from the customer’s perspective) becomes exceedingly simple, as the customer router
exchangesrouting information with only one (or a few) PE-router, whereas in the overlay VPN
network, the number ofneighbor routers can grow to a large number.
Routing between the customer sites is always optimal, as the provider routers know the

customer’s networktopology and can thus establish optimum inter-site routing.
Bandwidth provisioning is simpler because the customer has to specify only the inbound and
outboundbandwidths for each site (Committed Access Rate [CAR] and Committed Delivery Rate
[CDR]) and not theexact site-to-site traffic profile.
The addition of a new site is simpler because the service provider provisions only an additional
site andchanges the configuration on the attached PE-router. Under the overlay VPN model, the
service provider mustprovision a whole set of VCs leading from that site to other sites of the
customer VPN.
Prior to an MPLS-based VPN implementation, two implementation options existed for the peer-topeer VPNmodel:
The shared-router approach, where several VPN customers share the same PE-router.
The dedicated-router approach, where each VPN customer has dedicated PE-routers.