3Com 3C13636 Configuration Manual page 870

3Com Router 3000 Ethernet Family
Configuration Guide
The UPE implements the user access. It maintains the routes of VPN Site directly
connected with it. It does not maintain the routes of other remote Sites in VPN, or
only maintains their summary routes. The UPE assigns interior layer label to the
routes in its directly connected Site, and advertises the label to the SPE with VPN
routes through MP-BGP.
The SPE manages and advertises VPN routes. It maintains all the routes in the
VPN where its connected Site locates, including the routes in local and remote
Sites. The SPE does not advertise routes in remote Sites to UPE. It only
advertises the default route of VPN-instance or summary route to UPE with the
label.
Different roles result in different requirements for the SPE and UPE:
SPE: large capacity of routing table, high forwarding performance, few interface
resources
UPE: small capacity of routing table, low forwarding performance, high access
capability
The HoVPN takes advantage of the performance of SPEs and access capability of
UPEs.
It should be noted that the SPE and UPE are relative. In the hierarchical architecture,
the superstratum PE is SPE for the underlayer, and the Underlayer PE is UPE for the
superstratum.
The HoPE is the same as the traditional PE in appearance. It can exist together with
common PEs in an MPLS network.
2) SPE–UPE
The MP-BGP running between SPE and UPE can be either MP-IBGP or MP-EBGP.
This depends on whether UPE and SPE belong to the same AS.
When MP-IBGP is used, SPE acts as the route reflector in order to advertise routes
between IBGP peers. It advertises the VPN routes from the IBGP peer UPE to the peer
SPE, but it does not act as the route reflector of other PEs.
3) Embedment and extension of HoVPN
HoVPN supports the embedment of HoPE:
An HoPE can act as a UPE, and compose a new HoPE with another SPE.
An HoPE can act as the SPE, and compose a new HoPE with multiple UPEs.
Multiple embedment processes can be supported.
The embedment of HoPE can infinitely extend a VPN network in theory.
Chapter 3 BGP/MPLS VPN Configuration
3Com Corporation
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