In cases where VPN customers run OSPF and have areas that are multihomed into a provider network it is possible for loops to form.
What provision is made to prevent this?
A.
Use the OSPF "tag bit" on egress to the multihomed area from the PE.
B.
Set the OSPF "down bit" on egress to the multihomed area from the PE.
C.
Set the OSPF "down bit" on ingress from the multihomed area to the PE.
D.
Use the OSPF "tag bit" on ingress from the multihomed area to the PE.