What is the primary scope difference between OSPF and BGP?

• A. OSPF is an exterior gateway protocol for inter-domain routing between ASes.
• B. OSPF is an interior gateway protocol for fast convergence within an AS; BGP is an exterior gateway protocol for inter-domain routing between ASes.
• C. OSPF is used for WAN routing; BGP is used for LAN routing.
• D. OSPF uses distance-vector; BGP uses link-state.

Answer: (B)

The key idea is where the protocol operates: inside an autonomous system (intra-domain) or between autonomous systems (inter-domain). OSPF is an interior gateway protocol used for fast convergence within a single AS, providing quick, reliable routing inside that domain. BGP is an exterior gateway protocol used for inter-domain routing between different ASes, designed to scale across the whole Internet and enforce routing policies between domains. OSPF achieves fast convergence with a link-state approach and a hierarchical area design, while BGP uses a TCP-based path-vector mechanism to exchange reachability and policy information between ASes. This contrast—IGP for intra-domain with fast convergence vs EGP for inter-domain routing—is the primary scope difference. The other statements mischaracterize OSPF as exterior, misplace WAN/LAN roles, or misstate the underlying routing approaches.