3Com 3C13636 Configuration Manual page 868

3Com Router 3000 Ethernet Family
Configuration Guide
1) Site 1 sends an IPv4 packet with destination address 1.1.1.2 to CE1. CE1 looks
routing information up in the IP routing table and sends the packet to PE1.
2) PE1 looks up in the VPN-instance table according to the destination interface and
destination address to get MPLS label (or interior-layer label), LSP initialization
label (or exterior-layer label), BGP next hop (PE2), egress interface etc. When the
label stack is established, PE1 forwards via the egress interface the MPLS packet
to the first P on the LSP.
3) Every P router on the LSP forwards the MPLS packet according to the
exterior-layer label until the packet reaches the penultimate router, i.e. the P router
right before the PE2, which extracts the exterior-layer label and forwards the
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.
3.1.3 HoVPN
I. HoVPN Introduction
1) Hierarchical model and plane model
In BGP/MPLS VPN solutions the key devices, PEs, function in two aspects:
Providing access functions for users. PEs need a large number of interfaces.
Managing and advertising VPN routes, and processing user packets. PEs need
large-capacity memory and high forwarding capability.
Hierarchical architectures are mostly used in the current network schemes. For
example, the WAN architecture model contains three layers, namely, core layer,
convergence layer and access layer. The core layer requires the devices with the
highest performance among the three layers, while its network scale is the least.
However, BGP/MPLS VPN is a plane model, which requires the same performance on
all the PEs. If some PEs are limited in extending performance, all the network will be
influenced.
Because the plane model of BGP/MPLS VPN does not accord with the typical
hierarchical model, the scalability problem occurs in PE deployment at each layer. So
the plane model is not applicable to the large-scale VPN deployment.
2) HoVPN
To solve this problem, BGP/MPLS VPN needs to become the hierarchical model from
the plane model.
Chapter 3 BGP/MPLS VPN Configuration
3Com Corporation
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