Mpls L3Vpn Packet Forwarding; Mpls L3Vpn Networking Schemes - HP 12500 Series Configuration Manual

After a VPN instance is created, you can optionally configure a tunneling policy. 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.

MPLS L3VPN packet forwarding

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 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 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.
If two sites (CEs) belong to the same VPN and are connected to the same PE, each CE only needs to know
how to reach the other CE.
The following takes
Figure 49 VPN packet forwarding
Site 1
2.1.1.1/24
1.1.1.2
Site 1 sends an IP packet with the destination address of 1.1.1.2. CE 1 transmits the packet to PE
1.
1.
PE 1 searches VPN instance entries based on the inbound interface and destination address of the
2.
packet. Once finding a matching entry, PE 1 labels the packet with both inner and outer labels and
forwards the packet out.
The MPLS backbone transmits the packet to PE 2 by outer label. The outer label is removed from
3.
the packet at the penultimate hop.
PE 2 searches VPN instance entries according to the inner label and destination address of the
4.
packet to determine the outbound interface and then forwards the packet out the interface to CE 2.
CE 2 transmits the packet to the destination by IP forwarding.
5.

MPLS L3VPN networking schemes

In MPLS L3VPNs, VPN target attributes are used to control the advertisement and reception of VPN routes
between sites. They work independently and can be configured with multiple values to support flexible
VPN access control and implement multiple types of VPN networking schemes.
Figure 49 as an example to illustrate the VPN packet forwarding procedure.
CE 1
P
PE 1
Layer1
Layer2
1.1.1.2
P
PE 2
Layer2
1.1.1.2
1.1.1.2
195
Site 2
CE 2
1.1.1.2/24