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In other words, route target attributes define which sites can receive VPN-IPv4 routes, and from which
sites that a PE can receive routes.
Like RDs, route target attributes can be 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.
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 Border Gateway Protocol (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 redistribution 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 route 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 an import routing policy, an export routing policy, or
both as needed.
Tunneling policy
A tunneling policy is used to select the tunnel for the packets of a specific VPN instance to use.
After a VPN instance is created, you can optionally configure a tunneling policy for the VPN instance. By
default, only one tunnel is selected (no load balancing) in this order: LSP tunnel, CR-LSP tunnel. A
tunneling policy takes effect only within the local AS.
