How can you prevent multihomed customers with connections to two service providers from acting as a transit AS?

How can you prevent multihomed customers with connections to two service providers from acting as a transit AS?
A . Enable BGP synchronization on all the customer routers.
B . Use MED to influence the inbound traffic from the ISPs.
C . Use static routing to the ISPs.
D . Use an AS-path access-list to filter the BGP updates to the ISPs.
E . Use conditional advertisements when sending BGP updates to the ISPs.

View Answer

Answer: D