Which of the following internal routing protocols is best characterized as having fast convergence and being loop-free?

Border Gateway Protocol (BGP) is the main protocol used to exchange routing information between different autonomous systems on the internet. While BGP is robust and scalable, it is not designed for fast convergence; it operates on a path vector mechanism and typically has longer convergence times compared to internal routing protocols like OSPF.

Spanning Tree Protocol (STP) is primarily used to prevent loops in Ethernet networks by creating a loop-free logical topology. However, it is not a routing protocol and does not facilitate fast convergence in the context of IP routing. Its focus is on managing the data link layer rather than efficiently routing packets at the network layer.

Routing Information Protocol (RIP) is a distance-vector routing protocol that experiences slower convergence times due to its periodic updates and maximum hop count limitations. Although it is simple to configure, RIP is prone to routing loops and does not provide the fast convergence that OSPF does.