Router R5 receives four route updates for the same prefix. Which of the four routes will be installed in R5's routing table?

When a router receives multiple route updates for the same prefix, the decision on which route to install in its routing table is typically governed by the routing protocol's rules concerning administrative distance and metric. The route with the lowest administrative distance will be preferred.

In this situation, if we consider the routing protocols often used (such as OSPF, EIGRP, RIP, etc.), each of these protocols has an associated administrative distance that affects the routing decision. Generally, routes learned from directly connected interfaces have the highest priority, followed by static routes, and then dynamic routing protocols in a specific order.

If routes from R1 have the lowest administrative distance compared to those from R2, R3, and R4, they will be chosen and installed in R5's routing table. This means that R5 prioritizes routes based on the protocol that advertised them and the metrics associated with those routes.

In summary, if R5 has determined that the route from R1 is the most reliable due to its administrative distance or metric evaluation, it will install that route in the routing table, ensuring that the best possible path is utilized for that prefix.