HP MSR2000 series Configuration Manual page 404

VPN-IPv4 address
Traditional BGP cannot process overlapping VPN routes. If, for example, both VPN 1 and VPN 2 use
addresses on the segment 10.1 10.10.0/24 and each advertise a route to the segment, BGP selects only
one of them, which results in the loss of the other route.
PEs use MP-BGP to advertise VPN routes and use VPN-IPv4 address family to solve the problem with
traditional BGP.
A VPN-IPv4 address consists of 12 bytes. The first eight bytes represent the RD, followed by a four-byte
IPv4 address prefix.
Figure 128 VPN-IPv4 address structure
When a PE receives an ordinary IPv4 route from a CE, it must advertise 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 if the assigned RDs are unique. 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.
Configure a distinct RD for each VPN instance on a PE, so that routes to the same CE use the same RD.
The VPN-IPv4 address with an RD of 0 is a globally unique IPv4 address.
By prefixing a distinct RD to a specific IPv4 address prefix, you get 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 the
AS number and a discretionary number; or it can be related to an IP address, in which case it is the
combination of the IP address and a discretionary number.
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, 172.1.1.1:1.
• 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.
Route target attributes
MPLS L3VPN uses the BGP extended community attributes called "route target" attributes to control the
advertisement of VPN routing information.
A VPN instance on a PE supports the following types of route target attributes:
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