Cisco OL-21636-01 - Manual (Page 386)

E-12
Cisco IP Solution Center L2VPN and Carrier Ethernet User Guide, 6.0
OL-21636-01
Appendix E ISC Layer 2 VPN Concepts
VPLS Service Provisioning
Figure E-9 MPLS-Based VPLS Topology
The PE routers must create a full-mesh of emulated virtual circuits (VCs) to simulate the emulated LAN
seen by the CE devices. Forming a full-mesh of emulated VCs simplifies the task of emulating a LAN
in the provider core. One property of a LAN is to maintain a single broadcast domain. That is, if a
broadcast, multicast, or unknown unicast packet is received on one of the attachment circuits, it has to
be sent to all other CE devices participating in that VPLS instance. The PE device handles this case by
sending such a packet on all other attachment circuits and all the emulated circuits originating from that
PE. With a full-mesh of emulated VCs, such a packet will reach all other PE devices in that VPLS
instance. (See
Figure E-10 .)
Figure E-10 Full Mesh of Emulated VCs
CE
CE
CE
CE
Provider Core
Emulated LAN
CE Device Point-of-View
104081
Common VC ID
between PEs creates a
Virtual Switching Instance
CE
CE
CE
MPLS
104082
PE PE
MPLS enabled core
forms Tunnel LSPs
Attachment VCs are
Port Mode or VLAN ID
Full Mesh of directed
LDP sessions
exchange VC Labels