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Configuring MPLS L2VPN
MPLS L2VPN provides point-to-point and point-to-multipoint connections. This chapter describes only the
MPLS L2VPN technologies that provide point-to-point connections. For information about the MPLS
L2VPN technologies that provide point-to-multipoint connections, see "
."
Overview
MPLS L2VPN is an implementation of Pseudo Wire Emulation Edge-to-Edge (PWE3). It offers Layer 2
VPN services over an MPLS or IP backbone. MPLS L2VPN can transparently transmit Layer 2 data for
different data link layer protocols, including Ethernet, VLAN, ATM, FR, and PPP.
From a user's perspective, the MPLS or IP backbone is a Layer 2 switched network. For example, when
two Ethernet networks are connected through MPLS L2VPN over an MPLS backbone, Ethernet users think
they are connected directly through an Ethernet.
Basic concepts of MPLS L2VPN
•
Customer edge
—A CE is a customer device directly connected to the service provider network.
•
Provider edge
—A PE is a service provider device connected to one or more CEs. It provides VPN
access by mapping and forwarding packets between user networks and public tunnels.
•
Attachment circuit
—An AC is a link between a CE and a PE, such as an FR DLCI, ATM VPI/VCI,
Ethernet interface, VLAN, or PPP connection.
•
Pseudowire
—A PW is a virtual bidirectional connection between two PEs. An MPLS PW comprises
a pair of LSPs in opposite directions.
•
Public tunnel
—A public tunnel is a connection that carries one or more PWs across the MPLS or IP
backbone. It can be an LSP tunnel or an MPLS TE tunnel.
•
Cross-connect
—A cross-connect concatenates two physical or virtual circuits such as ACs and PWs.
It switches packets between the two physical or virtual circuits. Cross-connects include AC to AC
cross-connect, AC to PW cross-connect, and PW to PW cross-connect.
•
Site ID
—A site ID uniquely identifies a site in a VPN. Sites in different VPNs can have the same site
ID.
•
Route distinguisher
—A route distinguisher (RD) is added before a site ID to distinguish the sites that
have the same site ID but reside in different VPNs. An RD and a site ID uniquely identify a VPN site.
•
Label block
—A label block is a set of labels. It includes the following parameters:
{
Label base
—The LB specifies the initial label value of the label block. A PE automatically selects
an LB value that cannot be manually modified.
{
Label range
—The LR specifies the number of labels that the label block contains. The LB and LR
determine the labels contained in the label block. For example, if the LB is 1000 and the LR is
5, the label block contains labels 1000 through 1004.
{
Label-block offset
—The LO specifies the offset of a label block. If the existing label block
becomes insufficient as the VPN sites increase, you can add a new label block to enlarge the
label range. A PE uses an LO to identify the position of the new label block. The LO value of a
label block is the sum of the LRs of all previously assigned label blocks. For example, if the LR
