H3C Technologies H3C S12500-X Series Switches - Manual (Page 113)

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As shown in Figure 30 , a VPN-IPv4 address consists of 12 bytes. The first eight bytes represent the RD,
followed by a four-byte IPv4 prefix. The RD and the IPv4 prefix form a unique VPN-IPv4 prefix.
An RD can be in one of the following formats:
• When 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 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.
• When 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.
Route target attribute
MPLS L3VPN uses route target community attributes to control the advertisement of VPN routing
information. A VPN instance on a PE supports the following types of route target attributes:
• Export target attribute—A PE sets the export 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 received from
other PEs. If the export target attribute matches the import target attribute of a VPN instance, the PE
adds the routes to the routing table of the VPN instance.
Route target attributes define which sites can receive VPN-IPv4 routes, and from which sites a PE can
receive routes.
Like RDs, route target attributes can be one 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, 172.1.1.1:1.
• 32-bit AS number:16-bit user-defined number, where the minimum value of the AS number is 65536.
For example, 65536:1.
MP-BGP
MP-BGP supports multiple address families, including IPv4 multicast, IPv6 unicast, IPv6 multicast, and
VPN-IPv4 address families.
In MPLS L3VPN, MP-BGP advertises VPN-IPv4 routes for VPN sites between PEs.
MPLS L3VPN route advertisement
In a basic MPLS L3VPN, CEs and PEs are responsible for advertising VPN routing information. P routers
maintain only the routes within the backbone. A PE maintains only routing information for directly
connected VPNs, rather than for all VPNs.
VPN routing information is advertised from the local CE to the remote CE by using the following process:
1. From the local CE to the ingress PE:
The CE advertises standard IPv4 routing information to the ingress PE over a static route, RIP route,
OSPF route, IS-IS route, EBGP route, or IBGP route.