Operation Manual – MPLS L3VPN
H3C S9500 Series Routing Switches
Chapter 1 MPLS L3VPN Configuration
1-17
As shown in
Figure 1-13
, 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.
Note:
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 does not advertise routes of the remote sites to UPEs; it only
advertises to UPEs the default routes of VPN instances or summary routes along
with labels.
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.
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.
