Mpls L3Vpn Packet Forwarding - 3Com MSR 50 Series Configuration Manual

MPLS L3VPN Packet
Forwarding
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 of two types of formats:
16-bit AS number:32-bit user-defined number. For example, 100:1.
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32-bit IPv4 address:16-bit user-defined number. For example, 172.1.1.1:1.
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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.
After a VPN instance is created, you can optionally configure a tunneling policy. By
default, LSPs are used as tunnels and no load balancing occurs (in other words, the
number of tunnels for load balancing is 1). In addition, a tunneling policy takes
effect only within the local AS.
For basic MPLS L3VPN applications in a single AS, VPN packets are forwarded with
two layers of labels:
Layer 1 labels: Outer labels, used for label switching inside the backbone. They
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indicate LSPs from the local PEs to the remote PEs. Based on layer 1 labels, VPN
packets can be label switched along the LSPs to the remote PEs.
Layer 2 labels: Inner labels, used for forwarding packets from the remote PEs to
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the CEs. An inner label indicates to which site, or more precisely, to which CE
the packet should be sent. A PE finds the interface for forwarding a packet
according to the inner label.
MPLS L3VPN Overview 1463