Which of the following is a link state routing protocol?

RIPv2 is a distance vector protocol - it shares routing tables with directly connected neighbors rather than building a full topology map.

BGP (Border Gateway Protocol) is a path vector protocol used for inter-autonomous system routing on the Internet - it is neither link state nor distance vector.

IS-IS is a link state protocol in which each router floods Link State PDUs (LSPs) to all other routers, allowing every router to build an identical topology database of the entire network. Each router then independently runs the Dijkstra Shortest Path First (SPF) algorithm against this database to compute optimal routes, which is the defining behavior of a link state protocol.

RIP (version 1) is a distance vector protocol that uses hop count as its sole metric and shares routing tables with neighbors, not link state information.