Comparison of L3 and L2 VPNs

Table 19-3 shows a basic comparison between L3VPN and L2VPN solutions and describes the type of data each can carry.

Table 19-3. Comparison Between L3VPN and L2VPN

Layer 3 VPN (L3VPN)	Layer 2 VPN (L2VPN)
Provides packet-based forwarding (for example, IP).	Provides frame-based forwarding (for example, VLAN, DLCI, VPI/VCI).
Service provider forwards customer data packets based on Layer 3 information (for example, IP).	Service provider forwards customer data packets based on Layer 2 information. Supports Multiprotocol (for example, Ethernet, Frame Relay, or ATM).
SP involvement is required to perform routing.	No SP is involved. Uses Tunnel, circuit, LSP, MAC address.
Approaches include MPLS/BGP VPN (RFC 2547), MPLS VPN over IP, GRE, virtual router.	Concept is pseudowire.

Selecting L3VPN over L2VPN depends on how much control the enterprise wants to retain within its network. With L3VPN, the service provider is involved because it performs the routing; whereas with L2VPN, the service provider is not involved, because virtual tunnels and circuits are used instead.

Subscribers have various requirements and can take advantage of L3VPN and L2VPN as needed.

• L3VPN is useful to subscribers who prefer to outsource their routing to service providers. The service provider manages routing for the customer's sites.

• L2VPN is useful to subscribers who run their own Layer 3 networks over the WAN and require Layer 2 connectivity from service providers. In this case, the subscriber manages its own routing information.

Figure 19-5 illustrates the Layer 3 and Layer 2 VPN data forwarding scenarios over the MPLS core. Both Layer 3 and Layer 2 VPN services are offered from the edge of a network.

Figure 19-5. Layer 3 Versus Layer 2 VPN Forwarding

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