3com S7906E 설치 설명서
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You are recommended to configure a distinct RD for each VPN instance on a PE, guaranteeing that
routes to the same CE use the same RD. The VPN-IPv4 address with an RD of 0 is in fact a globally
unique IPv4 address.
By prefixing a distinct RD to a specific IPv4 address prefix, you make it a globally unique VPN IPv4
address prefix.
An RD can be related to an autonomous system (AS) number, in which case it is the combination of an
AS number and a discretionary number; or be related to an IP address, in which case it is the
combination of an IP address and a discretionary number.
An RD can be in either of the following two formats distinguished by the Type field:
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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.
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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, 172.1.1.1:1.
For the global uniqueness of an RD, you are not recommended to set the Administrator subfield to any
private AS number or private IP address.
VPN target attributes
BGP/MPLS VPN 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 two types of VPN target attributes:
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Export target attribute: A local PE sets this type of VPN target attribute for VPN-IPv4 routes learnt
from directly connected sites before advertising them to other PEs.
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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 a VPN-IPv4 route, and from which
sites a PE can receive routes.
Like RDs, VPN target attributes can be of two types of formats:
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16-bit AS number:32-bit user-defined number. For example, 100:1.
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32-bit IPv4 address:16-bit user-defined number. For example, 172.1.1.1:1.
Introduction to MCE
With BGP/MPLS VPN, data of private networks can be transmitted in the public network securely
through tunnels. However, in a typical BGP/MPLS VPN network, each VPN is connected to the PE
through a CE, as shown in
With the users’ increasing demand for service segmentation and security, a private network may be
divided into multiple VPNs, and the users of different VPN are usually isolated from each other. In a
private network containing multiple VPNs, users may be in such a dilemma: equipment investment and
the maintenance cost increment caused by assigning a CE for each of the VPNs; and potential data
security risks introduced by sharing one CE among multiple VPNs (because the same routing entry may
be used in multiple VPNs in this case).