Operation Manual – MCEH3C S3610&S5510 Series Ethernet Switches Chapter 1 MCE Overview1-4A 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 )IPv4 Address Prefix( 4-Byte )AdministratorSubfieldAssignedNumber SubfieldRoute Distinguisher ( 8-Byte )Figure 1-2 Structure of a VPN-IPv4 addressWhen a PE receives an ordinary IPv4 route from a CE, it must redistribute the VPNroute to the peer PE. The uniqueness of a VPN route is implemented by adding an RDto the route.A service provider can independently assign RDs provided the assigned RDs areunique. In this way, a PE can advertise different routes to VPNs even if the VPNs arefrom 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 addresswith 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 globallyunique VPN IPv4 address prefix.An RD can be related to an autonomous system (AS) number, in which case it is thecombination of an AS number and a discretionary number; or be related to an IPaddress, in which case it is the combination of an IP address and a discretionarynumber.An RD can be in either of the following two formats distinguished by the Type field:z When the value of the Type field is 0, the Administrator subfield occupies twobytes, 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.z When the value of the Type field is 1, the Administrator subfield occupies fourbytes, 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 Administratorsubfield to any private AS number or private IP address.V. VPN target attributesBGP/MPLS VPN uses the BGP extended community attributes called VPN targetattributes, or route target attributes, to control the advertisement of VPN routinginformation.A VPN instance on a PE supports two types of VPN target attributes:
