Nested Mpls L3Vpn Implementation - H3C S9500 Series Operation Manual

Operation Manual – MPLS L3VPN
H3C S9500 Series Routing Switches
1.1.1.1/24
Figure 1-4 Forwarding VPN packets
1) Site 1 sends an IPv4 packet with the destination address 1.1.1.2 of to CE1. CE1
looks up the IP routing table for a matched entry and sends the packet to PE1
according to the matched entry.
2) Depending on the interface the packet reaches and the destination of it, PE1 looks
up the VPN-instance entry to obtain interior-layer label, exterior-layer label, BGP
next hop (PE2), and output interfaces. After the establishment of labels, PE1
forwards MPLS packets to the first P of LSP through output interface.
3) Each P router on LSP forwards MPLS packets using exterior-layer label to the
penultimate-hop router, namely the P router before PE2. The penultimate-hop
router extracts the exterior-layer and sends MPLS packet to PE2.
4) PE2 looks up in the MPLS forwarding table according to the interior-layer label and
destination address to determine the egress interface for labeling operation and
the packet. It then extracts the interior-layer label and forwards through the egress
interface the IPv4 packet to CE2.
5) CE2 looks up in the routing table and sends the packet in normal IPv4 packet
forwarding mode to the site2.

1.1.3 Nested MPLS L3VPN Implementation

When implementing a nested MPLS L3VPN, pay attention to the following items:
No address overlap is allowed between user's internal sub-VPNs.
To ensure the VPN routing information is correctly advertised over the backbone
network, the VPN-Targets of the user VPN and the internal sub-VPNs cannot be
overlapped and must be specified by the service provider.
The provider PE and the customer PE must be directly connected and cannot
exchange VPNv4 route in Multihop-EBGP mode.
Before configuring a nested MPLS L3VPN, you must complete the following tasks:
Configuring IGP on the MPLS backbone network (including provider PE and P
routers) to implement the IP connectivity on the backbone network.
Configuring basic MPLS capability on the MPLS backbone network.
Configuring MPLS LDP and setting up LDP LSP on the MPLS backbone network.
Layer 1 Layer1
Layer 2 Layer2
1.1.1.2 1.1.1.2
1.1.1.2 1.1.1.2
CE1
Site 1
Chapter 1 MPLS L3VPN Configuration
Layer 2 Layer2
1.1.1.2 1.1.1.2
PE2
PE1
P
P
1-7
1.1.1.2 1.1.1.2
CE2
Site 2
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