An RD can be in one of the following formats distinguished by the Type field:
When the value of the Type field is 0, the Administrator subfield occupies two bytes, the Assigned
number subfield occupies four bytes, and the RD format is 16-bit AS number:32-bit user-defined
number. For example, 100:1.
When the value of the Type field is 1, the Administrator subfield occupies four bytes, the Assigned
number subfield occupies two bytes, and the RD format is 32-bit IPv4 address:16-bit user-defined
number. For example, 220.127.116.11:1.
When the value of the Type field is 2, the Administrator subfield occupies four bytes, the Assigned
number subfield occupies two bytes, and the RD format is 32-bit AS number:16-bit user-defined
number, where the minimum value of the AS number is 65536. For example, 65536:1.
To guarantee global uniqueness for an RD, do not set the Administrator subfield to any private AS
number or private IP address.
VPN target attributes
MPLS L3VPN uses the BGP extended community attributes called VPN target attributes or route target
attributes, to control the advertisement of VPN routing information.
A VPN instance on a PE supports the following types of VPN target attributes:
Export target attribute: A local PE sets this type of VPN target attribute for VPN-IPv4 routes learned
from directly connected sites before advertising them to other PEs.
Import target attribute: A PE checks the export target attribute of VPN-IPv4 routes advertised by
other PEs. If the export target attribute matches the import target attribute of the VPN instance, the
PE adds the routes to the VPN routing table.
In other words, VPN target attributes define which sites can receive VPN-IPv4 routes, and from which
sites that a PE can receive routes.
Similar to RDs, VPN target attributes can be of the following formats:
16-bit AS number:32-bit user-defined number. For example, 100:1.
32-bit IPv4 address:16-bit user-defined number. For example, 18.104.22.168:1.
32-bit AS number:16-bit user-defined number, where the minimum value of the AS number is 65536.
For example, 65536:1.
Using tunnels, MPLS L3VPN implements private network data transmission over the public network.
However, the traditional MPLS L3VPN architecture requires each VPN instance exclusively use a CE to
connect with a PE, as shown in
For better services and higher security, a private network is usually divided into multiple VPNs to isolate
services. To meet these requirements, you can configure a CE for each VPN, which increases users'
device expenses and maintenance costs. Or, you can configure multiple VPNs to use the same CE and
the same routing table, which sacrifices data security.
Using the MCE function of the switch, you can remove the contradiction of low cost and high security in
multi-VPN networks. With MCE configured, a CE can bind each VPN in a network with a VLAN interface
on the CE, and create and maintain a separate routing table (multi-VRF) for each VPN. This separates the
forwarding paths of packets of different VPNs and, in conjunction with the PE, can correctly advertise the
routes of each VPN to the peer PE, ensuring the normal transmission of VPN packets over the public