True or False: All policies are supported by the hop-by-hop routing paradigm.

• A. Not sure
• B. False
• C. True
• D. Depends on implementation

Answer: (B)

Hop-by-hop routing means each router makes forwarding decisions based on its own local view of the network and the next hop determined by the current routing policy. BGP’s policies can influence which routes are advertised and which paths are preferred at each hop, and they can be effective for many control goals at the network edge. However, not every policy can be realized through per-hop decisions alone. Some objectives require end-to-end guarantees or coordination across multiple networks, or rely on mechanisms beyond simple hop-by-hop decisions, such as traffic engineering across domains or enforcing path constraints that depend on the behavior of downstream providers. For example, insisting that traffic always traverses a specific country or a particular sequence of ASes across the entire path cannot be guaranteed purely by local hop-by-hop policies, since downstream routes may differ or change. Therefore, not all policies are supported by the hop-by-hop routing paradigm.