324
and LO of the first label block are 10 and 0, the LO of the second label block is 10. If the LR of
the second label block is 20, the LO of the third label block is 30.
A label block whose LB, LO, and LR are 1000, 10, and 5 is represented as 1000/10/5.
Assume that a VPN has 10 sites, and a PE assigns the first label block LB1/0/10 to the VPN.
When another 15 sites are added, the PE keeps the first label block and assigns the second label
block LB2/10/15 to extend the network. LB1 and LB2 are the initial label values that are randomly
selected by the PE.
•
Route target
—PEs use the BGP route target attribute (also called VPN target attribute) to manage
BGP L2VPN information advertisement. PEs support the following types of route target attributes:
{
Export target attribute
—When a PE sends L2VPN information to the peer PE in a BGP update
message, it sets the route target attribute in the update message to an export target. L2VPN
information includes the site ID, RD, and label block.
{
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,
the PE accepts the L2VPN information in the update message.
Route target attributes determine from which PEs a PE can receive L2VPN information.
MPLS L2VPN network models
As shown in
, this model connects two CEs through a PW on an MPLS or IP backbone.
Figure 82
MPLS L2VPN network model
To set up an MPLS L2VPN connection:
1.
Set up a public tunnel to carry one or more PWs between PEs:
The public tunnel can be an LSP or MPLS TE tunnel.
If multiple public tunnels exist between two PEs, you can configure a tunnel policy to control tunnel
selection. For more information about tunnel policies, see "
If a PW is established over an LSP or MPLS TE tunnel, packets on the PW have two labels. The outer
label is the public LSP or MPLS TE tunnel label that MPLS uses to forward the packet to the peer PE.
The inner label is the PW label that the peer PE uses to forward the packet to the destination CE.
2.
Set up a PW to connect customer networks:
PWs include static PWs, LDP PWs, BGP PWs, and Circuit Cross Connect (CCC) PWs.
To establish a static PW, configure the peer PE address, and the incoming and outgoing PW labels
for the PW on the two PEs. Static PWs consume a small amount of resources but have complex
configurations.
