R3303-HP HSR6800 Routers MPLS Configuration Guide

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Figure 40 Label distribution in Martini mode
Kompella MPLS L2VPN
Kompella MPLS L2VPN employs two levels of labels to transfer user packets, and uses BGP as the
signaling protocol to distribute the inner VC label.
Different from other MPLS L2VPN modes, Kompella introduces the concept of VPN. It allows CEs in the
same VPN to establish a connection. CEs in different VPNs cannot establish a connection.
Kompella MPLS L2VPN has the following basic concepts:
• CE ID—Kompella numbers CEs inside a VPN. A CE ID uniquely identifies a CE in a VPN. CEs in
different VPNs can have the same CE ID.
• Route distinguisher—To distinguish CEs with the same CE ID in different VPNs, Kompella adds an
RD before a CE ID. An RD and a CE ID uniquely identify a CE.
• Route target—Kompella uses the BGP route target attribute (also called "VPN target" attribute) to
identify VPNs to make sure CEs in the same VPN can establish a connection and CEs in different
VPNs cannot.
A PE supports the following types of route target attributes:
• Export target attribute—When a PE sends L2VPN information (such as CE ID and RD) to the peer
PE through a BGP update message, it sets the route target attribute carried in the update message
to export target.
• Import target attribute—When a PE receives an update message from the peer PE, it checks the
route target attribute in the update message. If the route target value matches an import target on
the PE, the PE accepts the L2VPN information in the update message.
In a word, route target attributes define which PEs can receive L2VPN information, and from which PEs
that a PE can receive L2VPN information.
Different from Martini mode, the Kompella mode does not distribute the VC label assigned by the local
PE directly to the peer PE through the signaling protocol. Instead, it uses label blocks to assign labels to
multiple connections at a time. A PE advertises label blocks to all PEs in the same VPN. Each PE calculates
the VC labels according to the label blocks from other PEs.
A label block includes the following parameters:
• Label Base—Initial label value of the label block. A PE automatically selects the LB value that cannot
be manually modified.
• Label Range—Number of labels that the label block contains. LB and LR determine the labels
contained in the label block. For example, if the LB is 1000 and LR is 5, the label block contains
labels 1000 through 1004.