The VPN named my_vpn is operating on interface s0/0 of a PE-router. The CE-PE routing protocol
is OSPF. The MPLS backbone IPG is OSPF.
Which statement is true about the interaction between the customer’s OSPF routes and the
backbone’s OSPF routes?
A.
On the PE-router, two instances of OSPF are run: one for the VPN and one for the backbone
IGP.
B.
On the PE-router, three instances if OSPF are run: one for the VPN, one for the backbone IGP,
and one to carry the PE-PRE routes.
C.
This configuration is acceptable for MPLS implementations.
However, when MPLS VPNs are implemented, OSPF cannot be used as the CE-PE routing
protocol and
the backbone IGP.
D.
On the PE-router, a single instance of OSPF is run.
However, the customer’s routes are kept separate for the backbone route because the RD is
prepares to
the customer’s routes.
Explanation:
It is important to note that the MPLS/VPN backbone is not a real OSPF area 0 backbone. No
adjacencies are formed between PE routers – only between PE and CE routers. MP-iBGP is used
between PE routers, and all OSPF routes are translated into VPN-IPv4 routes. This means that
the redistribution of routes into BGP does not cause these routes to become external OSPF routes
when advertised to other member sites of the same VPN. Reference: MPLS and VPN
Architectures (Ciscopress) page 235