C2 Ethernet Topologies

This section discusses the EoMPLS topology solutions that will be addressed in this chapter. From the perspective of the SP to customer interconnect, the three scenarios are as follows:

Ethernet single point-to-point connectivity? Provides a single, port-based Ethernet connection between two physical data ports provided across an MPLS network, which is the foundation for VPWS.
The port may operate in a direct Ethernet ARPA encapsulation mode or in an 802.1Q encapsulation format, but all traffic entering that physical port will be transported to a remote end without alteration.
Generally, such a design would be used with a Layer 3 customer network where the typical WAN serial links are replaced with higher speed point-to-point facilities. Alternatively, the customer network may comprise a Layer 2 domain where the customer desires to interconnect various LAN islands into a larger whole using the SP's Layer 2 services. In either case, the Layer 2 VPN network is a transport for customer frames in a similar manner as a set of dedicated links.
Multiple Ethernet point-to-point connectivity? This concept builds on the previous scenario by allowing for subinterface (VLAN)?based point-to-point connections across the WAN cloud. VLANs defined on the physical port may be switched to differing destination endpoints in this model. Typically, the customer network is a Layer 3 entity and the customer is seeking a service from the SP analogous to a traditional Frame Relay or ATM offering.
Multipoint mesh connectivity? While efforts are underway in various vendor communities and standards bodies to provide multipoint L2VPN connectivity, these mechanisms are not yet generally available. The previous two scenarios simply provide one or more point-to-point connections to allow for the desired degree of network meshing. In the future, this meshing (or bridging, if preferred) will use the service provider network resources to provide true multipoint connectivity; that is, from the customer edge's perspective, a single connection into the service provider network that has the appearance of a LAN interconnect (or bridged interconnect) to some or all of the customer's other CE gear. This approach is frequently referred to as transparent LAN services (TLS), which is the foundation for VPLS.

Figure 7-1 summarizes these topology examples, note that hub-and-spoke and ring implementations are options for deployment at the customer locations.