Border Gateway Protocol (BGP) is the primary protocol used to route traffic on the public internet. It allows ISPs and large networks to exchange routing information, making it an Exterior Gateway Protocol (EGP).

Breakdown of Options:

A. BGP – Correct answer. Used for internet routing and exchanges routing information between ISPs.

B. OSPF – An Interior Gateway Protocol (IGP) used for routing within an autonomous system (not the public internet).

C. EIGRP – Cisco’s proprietary IGP, used within private networks, not the public internet.

D. RIP – An older distance-vector protocol, not scalable for the internet.