H3C Technologies H3C S12500-X Series Switches - Manual (Page 125)

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• A UPE provides user access. It maintains the routes of directly connected VPN sites. It does not
maintain the routes of the remote sites in the VPN, or it only maintains their summary routes. A UPE
assigns inner labels to the routes of its directly connected sites, and advertises the labels along with
VPN routes to the SPE through MP-BGP.
• An SPE manages and advertises VPN routes. It maintains all the routes of the VPNs connected
through UPEs, including the routes of both the local and remote sites. An SPE advertises routes
along with labels to UPEs, including the default routes of VPN instances or summary routes and the
routes permitted by the routing policy. By using routing policies, you can control which sites in a
VPN can communicate with each other.
Different roles mean different requirements:
• An SPE must have a large routing table capacity and high forwarding performance but needs fewer
interface resources.
• A UPE must have higher access capability but needs a small routing table capacity and low
forwarding performance.
HoVPN makes full use of both the high performance of SPEs and the high access capability of UPEs.
The concepts of SPE and UPE are relative. In the hierarchical PE architecture, a PE might be the SPE of its
underlayer PEs and a UPE of its SPE at the same time.
The HoPE and common PEs can coexist in an MPLS network.
SPE-UPE
Either MP-IBGP or MP-EBGP can run between SPE and UPE.
For MP-IBGP to advertise routes between IBGP peers, the SPE acts as the RR and advertises routes from
IBGP peer UPE to IBGP peer SPE. However, it does not act as the RR of the other PEs.
Recursion and extension of HoVPN
HoVPN supports HoPE recursion:
• An HoPE can act as a UPE to form a new HoPE with an SPE.
• An HoPE can act as an SPE to form a new HoPE with multiple UPEs.
• HoVPN supports multi-level recursion.
Figure 43 Recursion of HoPEs
Figure 43 shows a three-level HoPE. The PE in the middle is called the "middle-level PE (MPE)." MP-BGP
runs between SPE and MPE, and between MPE and UPE.