PLANET XGS3-24042 - Manual (Page 675)

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 Import Target Attribute: when receiving the VPN-IPv4 route advertised by other PE routers, PE will
check their Export Target Attribute, and add the routes into corresponding VPN route table only
when their Export Target attributes match the Import Target attributes of the VPN instances on it.
In other words, VPN Target attribute defines which sites can accept a VPN-IPv4 route, and a PE router can
receive routes from witch sites.
Like RD, there are two VPN Target formats:
 16 bits ASN : 32bits user-defined number, for example: 100:1
 32bits IPv4 address: 16 bits user-defined number, for example: 172.1.1.1:1
MP-BGP
MP-BGP (Multiprotocol extensions for BGP-4) transmits VPN information and routes between PE routers.
MP-BGP is backward-compatible, simultaneously supporting traditional IPv4 address family and other
address family (such as VPN-IPv4 address family). It can ensure the advertisement of private network VPN
routes only happens within the VPN, and can realize the communication between MPLS VPN members.
Routing Policy
On the basis of controlling VPN route advertisement via ingress and egress extended community, the import
or export route policy can be used for a more precise control of importing and advertising VPN routes.
The import route policy can filter the routes importable for VPN instances according to the VPN target attribute
of routes. It can deny the receipt of routes specified by the community in the import list. The export route
policy can deny advertising the routes specified by the community in the export list.
After creating VNP instances, users can choose whether to configure import or export route policy.
Tunneling Policy
Tunneling Policy is used to choose tunnels for specified VPN instances messages.
Tunneling Policy is optional. After creating VNP instances, users can configure it. By default, it will choose
LSP as the tunnel without load sharing (the load sharing number is 1). Besides, this policy only takes effect in
one AS domain.
81.1.3 Forwarding BGP/MPLS VPN Messages
In basic L3VPN applications (not include Multi-AS VPN), the forwarding of VPN packets adopts the 2-layer
label mode:
 The first layer (outer layer) labels will be switched within the backbone network, indicating a LSP
from the PE to the remote PE. With this layer of label, VPN messages can reach the remote PE
along the LSP.
 The second layer label (inner layer) will be used when the packet reaches CE from the remote PE,
indicating which site to send the packet, or, more specifically, which CE it will reach. Thus the remote
PE will find the correct interface to forward the packet according to this layer of label.
In some special conditions, two sites belonging to the same VPN may connect to a same PE, in which case,
the only information matters is how to reach the remote CE.
The next figure demonstrates an example of forwarding VPN packets: