HP 12500 Series Configuration Manual page 202

A VPN instance on a PE supports two types of VPN target attributes:
Export target attribute—A local PE sets this type of VPN 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 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 VPN-IPv4 routes, and from
which sites that a PE can receive routes.
Like RDs, VPN target attributes can be 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.
SoO
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The Site of Origin (SoO) attribute specifies the site where the route update is originated. It prevents
the receiving router from advertising the route update back to the originating site. If the AS-path
attribute is lost, the router can use the SoO attribute to avoid routing loops.
The SoO attribute has 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.
NOTE:
A route update can contain one SoO attribute at most.
MP-BGP
Multiprotocol extensions for BGP-4 (MP-BGP) advertises VPN composition information and routes
between PEs. It is backward compatible and supports both traditional IPv4 address family and other
address families, such as VPN-IPv4 address family.
Using MP-BGP can guarantee that private routes of a VPN are advertised only in the VPN and implement
communications between MPLS VPN members.
Routing policy
In addition to the import and export extended communities for controlling VPN route advertisement, you
can also configure import and export routing policies to control the injection and advertisement of VPN
routes more precisely.
An import routing policy can further filter the routes that can be advertised to a VPN instance by using
the VPN target attribute of import target attribute. It can reject the routes selected by the communities in
the import target attribute. An export routing policy can reject the routes selected by the communities in
the export target attribute.
After a VPN instance is created, you can configure import and/or export routing policies as needed.
Tunneling policy
A tunneling policy is used to select the tunnel for the packets of a specific VPN instance to use.
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