H3C S3610-28P Operation Manual page 1420

Operation Manual – MCE
H3C S3610&S5510 Series Ethernet Switches
A VPN-IPv4 address consists of 12 bytes. The first eight bytes represent the RD,
followed by a 4-byte IPv4 address prefix, as shown in.
Type Field
( 2-Byte )
Figure 1-2 Structure of a VPN-IPv4 address
When a PE receives an ordinary IPv4 route from a CE, it must redistribute the VPN
route to the peer PE. The uniqueness of a VPN route is implemented by adding an RD
to the route.
A service provider can independently assign RDs provided the assigned RDs are
unique. In this way, a PE can advertise different routes to VPNs even if the VPNs are
from different service providers and are using the same IPv4 address space.
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:
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, 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.
V. 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:
Route Distinguisher ( 8-Byte )
Administrator
Subfield
Assigned IPv4 Address Prefix
Number Subfield
1-4
Chapter 1 MCE Overview
( 4-Byte )