176
Figure 54
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, and between MPE and UPE.
MP-BGP advertises the following routes:
•
All the VPN routes of UPEs to the SPEs.
•
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. Each UPE maintains only VPN routes of its
directly connected sites. An MPE has fewer routes than the SPE but has more routes than a UPE.
OSPF VPN extension
This section describes the OSPF VPN extension. For more information about OSPF, see
Layer 3—IP
Routing Configuration Guide
.
OSPF for VPNs on a PE
If OSPF runs between a CE and a PE to exchange VPN routes, the PE must support multiple OSPF
instances to create independent routing tables for VPN instances. Each OSPF process is bound to a VPN
instance. Routes learned by an OSPF process are added into the routing table of the bound VPN
instance.
OSPF area configuration between a PE and a CE
The OSPF area between a PE and a CE can be either a non-backbone area or a backbone area.
In the OSPF VPN extension application, the MPLS VPN backbone is considered the backbone area (area
0). The area 0 of each VPN site must be connected to the MPLS VPN backbone (physically connected or
logically connected through a virtual link) because OSPF requires that the backbone area be contiguous.
BGP/OSPF interaction
If OSPF runs between PEs and CEs, each PE redistributes BGP routes to OSPF and advertises the routes
to CEs through OSPF. OSPF considers the routes redistributed from BGP as external routes but the OSPF
routes actually might belong to the same OSPF domain. This problem can be resolved by configuring the
same domain ID for sites in an OSPF domain.
