H3C Technologies H3C S7500E Series Switches - Manual (Page 242)

6-17
Figure 6-14 Basic architecture of HoVPN
MPLS network
PE PE
SPE UPE UPE
CE CE CE CE
VPN 1 VPN 1 VPN 2 VPN 2
Site 1 Site 2
As shown in Figure 6-14 , devices directly connected to CEs are called underlayer PEs (UPEs) or
user-end PEs, whereas devices that are connected with UPEs and are in the internal network are
called superstratum PEs (SPE) or service provider-end PEs.
The hierarchical PE consists of multiple UPEs and SPEs, which function together as a traditional PE.
With the HoVPN solution, PE functions are implemented hierarchically. Hence, the solution is also
called hierarchy of PE (HoPE).
UPEs and SPEs play different roles:
z
A UPE allows user access. It maintains the routes of the VPN sites that are directly connected
with it, It does not maintain the routes of the remote sites in the VPN, or only maintains their
summary routes. A UPE assigns inner labels to the routes of its directly connected sites, and
advertises the labels to the SPE along with VPN routes through MP-BGP.
z
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 nodes
in a VPN can communicate with each other.
Different roles mean different requirements:
z
SPE: An SPE is required to have large-capacity routing table, high forwarding performance, and
fewer interface resources.
z
UPE: A UPE is required to have small-capacity routing table, low forwarding performance, but
higher access capability.
HoVPN takes full use of both the high performance of SPEs and the high access capability of UPEs.