Which Routing Protocol is Installed in the Routing Table?

B.

With the same route (prefix), the router will choose the routing protocol with lowest Administrative Distance (AD) to install into the routing table.

The AD of Internal EIGRP (90) is lowest so it would be chosen.

The table below lists the ADs of popular routing protocols.

Note: The AD of IS-IS is 115

The EIGRP in the table above is Internal EIGRP.

The AD of External EIGRP is 170

An EIGRP external route is a route that was redistributed into EIGRP.

The answer to this question depends on the administrative distance of each routing protocol. Administrative distance (AD) is a value used by routers to choose between different routing protocols when they receive multiple routes for the same destination. The lower the AD value, the more preferred the route.

The administrative distances for the four routing protocols mentioned in the question are as follows:

• IS-IS: AD = 115
• OSPF: AD = 110
• RIP: AD = 120
• EIGRP: AD = 90 (internal) or 170 (external)

In this scenario, R1 has learned route 192.168.12.0/24 via all four routing protocols, which means that it has multiple routes to the same destination. To determine which route will be installed in the routing table, R1 will consider the administrative distance of each protocol. The protocol with the lowest AD value will be preferred.

In this case, the internal EIGRP route has the lowest AD value of 90, so it will be installed in the routing table under normal operating conditions. Therefore, the correct answer is B. Internal EIGRP.