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Figure 60 Basic architecture of HoVPN
As shown in
Figure
60, UPEs and SPEs play the following different roles:
•
A UPE is directly connected to CEs. It 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.
A UPE features high access capability, small routing table capacity, and low forwarding
performance.
•
An SPE is connected to UPEs and resides inside the service provider network. It 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. An SPE features large routing table capacity, high
forwarding performance, and fewer interface resources.
Either MP-IBGP or MP-EBGP can run between SPE and UPE. When MP-IBGP runs between SPE
and UPEs, the SPE acts as the RR of multiple UPEs and reflects routes between UPEs.
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 multilevel recursion. In HoPE recursion, the concepts of SPE and UPE are relative.
A PE might be the SPE of its underlayer PEs and a UPE of its SPE at the same time.
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