H3C Technologies H3C S6800 Series Switches - Manual (Page 177)

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2. From the ingress PE to the egress PE:
The ingress PE performs the following operations:
a. Adds RD and route target attributes to these standard IPv4 routes to create VPN-IPv4 routes.
b. Saves them 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 performs the following operations:
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 or an MPLS TE tunnel. Based on the outer tag, a VPN packet can be forwarded along the
public tunnel to the remote PE. 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 routes among PEs.
Figure 42 VPN packet forwarding
As shown in Figure 42 , a VPN packet is forwarded from Site 1 to Site 2 by using the following process:
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 performs the following operations:
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.
3. P devices forward the packet to PE 2 by the MPLS label. The MPLS label is removed from the packet
at the penultimate hop.
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