Multipoint Layer 2
Services enable geographically separated local-area network (LAN) segments to
be interconnected as a single bridged domain over an MPLS network. The full
functions of the traditional LAN such as MAC address learning, aging, and
switching are emulated across all the remotely connected LAN segments that are
part of a single bridged domain. A service provider can offer VPLS service to
multiple customers over the MPLS network by defining different bridged domains
for different customers. Packets from one bridged domain are never carried over
or delivered to another bridged domain, thus ensuring the privacy of the LAN
service.
Note |
Multipoint Layer 2 services are also called as Virtual Private LAN
Services.
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Multipoint Layer 2
Services transports Ethernet 802.3, VLAN 802.1q, and VLAN-in-VLAN (Q-in-Q)
traffic across multiple sites that belong to the same Layer 2 broadcast domain.
It offers simple Virtual LAN services that include flooding broadcast,
multicast, and unknown unicast frames that are received on a bridge. The
Multipoint Layer 2 Services solution requires a full mesh of pseudowires that
are established among provider edge (PE) routers. The Multipoint Layer 2
Services implementation is based on Label Distribution Protocol (LDP)-based
pseudowire signaling.
A VFI is a virtual
bridge port that is capable of performing native bridging functions, such as
forwarding, based on the destination MAC address, source MAC address learning
and aging.
After provisioning
attachment circuits, neighbor relationships across the MPLS network for this
specific instance are established through a set of manual commands identifying
the end PEs. When the neighbor association is complete, a full mesh of
pseudowires is established among the network-facing provider edge devices,
which is a gateway between the MPLS core and the customer domain.
The service provider
network starts switching the packets within the bridged domain specific to the
customer by looking at destination MAC addresses. All traffic with unknown,
broadcast, and multicast destination MAC addresses is flooded to all the
connected customer edge devices, which connect to the service provider network.
The network-facing provider edge devices learn the source MAC addresses as the
packets are flooded. The traffic is unicasted to the customer edge device for
all the learned MAC addresses.
Multipoint Layer 2
Services require the provider edge device to be MPLS-capable. The Multipoint
Layer 2 Services provides edge device holds all the VPLS forwarding MAC tables
and Bridge Domain information. In addition, it is responsible for all flooding
broadcast frames and multicast replications.