Mpls L3Vpn Packet Forwarding - HP MSR2000 Configuration Manual

2. From the ingress PE to the egress PE:
The ingress PE does the following:
a. Adds RDs and route target attributes to these standard IPv4 routes to create VPN-IPv4 routes.
b. Saves the VPN-IPv4 routes to the routing table of the VPN instance created for the CE.
c. Advertises the VPN-IPv4 routes to the egress PE through MP-BGP.
3. From the egress PE to the remote CE:
After receiving the VPN-IPv4 routes, the egress PE does the following:
a. Compares the routes' export target attributes with the local import target attributes.
b. Adds the routes to the routing table of the VPN instance if the export and local import target
attributes match each other.
c. Restores the VPN-IPv4 routes to the original IPv4 routes.
d. Advertises those routes to the connected CE over a static route, RIP route, OSPF route, IS-IS
route, EBGP route, or IBGP route.

MPLS L3VPN packet forwarding

In a basic MPLS L3VPN (within a single AS), a PE adds the following information into VPN packets:
Outer tag—Identifies the public tunnel from the local PE to the remote PE. The public tunnel can be
•
an LSP, an MPLS TE tunnel, or a GRE tunnel. Based on the outer tag, a VPN packet can be
forwarded along the public tunnel to the remote PE. For a GRE public tunnel, the outer tag is the
GRE encapsulation. For an LSP or MPLS TE tunnel, the outer tag is an MPLS label.
• Inner label—Identifies the remote VPN site. The remote PE uses the inner label to forward packets
to the target VPN site. MP-BGP advertises inner labels for VPN-IPv4 routes among PEs.
Figure 42 VPN packet forwarding
Site 1
2.1.1.1/24
1.1.1.2
As shown in
1. Site 1 sends an IP packet with the destination address 1.1.1.2. CE 1 transmits the packet to PE 1.
2. PE 1 does the following:
a. Finds the matching VPN route based on the inbound interface and destination address of the
packet.
b. Labels the packet with both the inner label and the outer tag.
c. Forwards the packet to the public tunnel.
CE 1
PE 1
Outer tag
Inner label
1.1.1.2
Figure 42, a VPN packet is forwarded from Site 1 to Site 2 by using the following process:
P P
MPLS network
Inner label
1.1.1.2
169
Site 2
CE 2
PE 2
1.1.1.2/24
1.1.1.2