H3C Technologies H3C S7500E Series Switches User Manual
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Note that the concepts of SPE and UPE are relative. In the hierarchical PE architecture, a PE may 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.
2) SPE-UPE
The MP-BGP running between SPE and UPE can be either MP-IBGP or MP-EBGP. Which one to use
depends on whether the UPE and SPE belong to a same AS.
With MP-IBGP, in order 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.
3) Recursion and extension of HoVPN
HoVPN supports HoPE recursion:
z
A HoPE can act as a UPE to form a new HoPE with an SPE.
z
A HoPE can act as an SPE to form a new HoPE with multiple UPEs.
z
HoVPN supports multi-level recursion.
With recursion of HoPEs, a VPN can be extended infinitely in theory.
Figure 6-15
Recursion of HoPEs
shows a three-level HoPE. The PE in the middle is called the middle-level PE (MPE).
MP-BGP runs between SPE and MPE, as well as between MPE and UPE.
The term of MPE does not really exist in a HoVPN model. It is used here just for the convenience of
description.
MP-BGP advertises all the VPN routes of the UPEs to the SPEs, and advertises the default routes of
the VPN instance of the SPEs or the VPN routes permitted by the routing policies to the UPEs.
The SPE maintains the VPN routes of all sites in the HoVPN, while each UPE maintains only VPN
routes of its directly connected sites. The number of routes maintained by the MPE is between the
above two.