R2511-HP MSR Router Series MPLS Configuration Guide(V5)

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As shown in Figure 22, CE 1 and CE 2 belong to VPN 1. CE 3 and CE 4 belong to VPN 2. Configure
route targets for the two VPNs to make sure CEs in the same VPN can set up a VC and CEs in different
VPNs cannot.
A VC is set up as follows (take the VC between CE 1 and CE 2 as an example):
1. PE 1 sends the RD, CE ID, route target (export target configured for VPN 1 on PE 1), and the label
block for CE 1 to PE 2 in a BGP update message.
2. When PE 2 receives the update message, it compares the route target in the message against the
import targets locally configured for VPNs. If a match is found, PE 2 learns the L2VPN information
in the update message for the matching VPN. Otherwise, it does not learn the L2VPN information.
In this example, the route target value carried in the update message for CE 1 is 100:1, which
matches the import target of VPN 1 on PE 2. Therefore, PE 2 adds the CE 1 L2VPN information
only to VPN 1 but not to other VPNs.
3. PE 2 sends a BGP update message for CE 2 to PE 1. PE 1 processes the update message as PE 2
does.
4. PE 1 and PE 2 calculate the local and remote VC labels for the VC according to the learned L2VPN
information.
The VC is successfully set up after both PE 1 and PE 2 calculate the VC labels.
Table 1 c
ompares the implementation modes of MPLS L2VPN.
Table 1 Comparing MPLS L2VPN implementation modes
Mode
VC label encapsulation
and distribution
Advantages and disadvantages
Application
scenario
CCC
VC label encapsulation:
one level of label
VC label distribution:
static configuration
Advantages:
• Requires no signaling protocol and occupies
fewer network resources.
• Network devices only need to support MPLS.
• Better QoS for service traffic as LSPs are
exclusive to CCC connections.
• Supports local and remote connections.
Disadvantages:
• Configuration and maintenance are
complicated. You must configure two static LSPs
in opposite directions for each CCC connection
on each P device.
• Cannot automatically adapt to network
changes.
Small-scale
network with a
simple
topology
where all
network
devices
support MPLS.
SVC
VC label encapsulation:
two levels of labels
VC label distribution:
static configuration
Advantage: Requires no signaling protocol and
occupies few network resources.
Disadvantage:
• Cannot automatically adapt to network
changes.
• Supports only remote connections.
Small-scale
network with a
simple
topology.