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DES-7200 Configuration Guide Chapter 2 Configuring BGP IP VPN
2-5
Figure 6 RT structure
The definition of RT is similar to that of RD. For 0x02 and 0x202, the AS number must be a public
one. For 0x102, the IPv4 address must be a global one rather than a private address.
2.1.3 MP-BGP
The VPN route information is transmitted on the backbone network through BGP. The export RT
attribute is carried in the BGP extended community attribute. The traditional BGP4, however,
transmits only IPv4 routes and cannot carry the VPN route that includes RDs. Therefore, the
BGP is extended to introduce new attributes. One of the biggest advantages of BGP is its
scalability. The Multi-Protocol (MP-BGP) is a new attribute introduced to the original BGP to
support multiple protocols. The MP-BGP can carry VPN information. In this manner, the VPN
route takes up the form of RD + IP address prefix. By adding RDs to VPN routes exchanged
between PEs, the MP-BGP allows VPN users to change the IPv4 routes to VPN-IPv4 routes and
transmit them on the backbone network.
2.1.4 Protocol Specifications
IETF RFC 4364: BGP/MPLS IP Virtual Private Networks (VPNs)
2.2 Default Configurations
By default, BGP/MPLS L3 VPN is disabled.
Functions Default Setting
Basic BGP/MPLS L3 VPN
functions
Disabled
VPN label distribution mode Assigning labels to each VRF
Inter-AS VPN Disabled
CSC VPN Disabled
MPLS VPN Over GRE Disabled