This offers simpler configuration than interconnecting
the routers over Ethernet pseudowires (where a separate VLAN pseudowire would
need to be configured between each pair of routers).
?– Switch interconnection In this application, a VPLS instance connects multiple
customer Ethernet switches and/or hosts. Although there are advantages in being
able to connect switches directly to the SP??™s network at Layer 2, this ability brings
with it potential scalability issues that will be discussed in the VPLS scaling
section below.
VPLS Architecture As with pseudowires, a key requirement in the VPLS architecture
was to reuse as much as possible from existing IP/MPLS router capabilities. Since the
LDP VPLS effort lagged the pseudowire effort by two years, those existing capabilities
were assumed to include both Ethernet pseudowire forwarding and LDP signalling for
pseudowires.
The basic VPLS architecture consists of a set of PEs, with a full mesh of MPLS LSPs
between them (however established). For each VPLS instance, a full mesh of Ethernet
pseudowires is provisioned to interconnect the PEs that are members of the VPLS, and
then each PE acts as a multipoint learning Ethernet bridge with one port per pseudowire
and one per local attachment circuit.
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