H3C S9500 Series Operation Manual page 7

Operation Manual – MPLS L3VPN
H3C S9500 Series Routing Switches
1) Between CE and PE
A PE router can learn routing information about the CE connected to it through static
route, RIP (supporting multi-instance), OSPF (supporting multi-instance) or EBGP, and
imports it in a vpn-instance.
2) Between ingress PE and egress PE
The ingress PE router uses MP-BGP to send information across public network: It
advertises routing information learned from CE to the egress PE router (with MPLS
label) and learns the CE routing information learned at the egress PE router.
The internal connectivity among the VPN internal nodes is ensured through enabling
IGP (for example, RIP and OSPF) or configuring static routes on the PEs.
3) LSP setup between PEs
LSPs must be set up between PEs for VPN data traffic forwarding with MPLS LSP. The
PE router which receives packets from CE and create label protocol stack is called
Ingress LSR, while the BGP next hop (Egress PE router) is Egress LSR. Using LDP to
create fully connected LSPs among PEs.
4) Between PE and CE
A CE can learn remote VPN routes from the PE connected through static routes, RIP,
OSPF or EBGP.
With above-mentioned steps, reachable routes can be established between CEs, for
transmission of VPN private routing information over public network.
II. Forwarding VPN packets
On the ingress PE, two-layer label stack is formed for each VPN packet:
Interior-layer label, also called MPLS label, is at the bottom of the label stack and
distributed by M-BGP when the egress PE advertises routing information (in VPN
forwarding table) to ingress GE. When VPN packets from public network reach the CE,
they can be forwarded from the designated interface to the designated CE or site by
searching for the target MPLS forwarding table according to the labels contained.
Exterior-layer label, known as LSP initialization label, distributed by MPLS LDP, is at
the top of the label stack and indicates an LSP from the ingress PE to egress PE. By the
switching of exterior-layer label, VPN packets can be forwarded along the LSP to the
peer PE.
Figure 1-4 illustrates the details:
Chapter 1 MPLS L3VPN Configuration
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