OSPF Route Selection:

# Selecting Routes in OSPF

### Question

When OSPF learns multiple paths to a network, how does it select a route?

### Explanations

Click on the arrows to vote for the correct answer

A. B. C. D.

C

OSPF (Open Shortest Path First) is a link-state routing protocol that determines the shortest path to a destination network based on the lowest metric or cost. OSPF learns multiple paths to a network through the exchange of link-state advertisements (LSAs) between neighboring routers.

When OSPF receives multiple paths to a network, it uses a Dijkstra algorithm to calculate the shortest path to the network based on the lowest cost or metric. The cost of a path is determined by the bandwidth of the links along the path.

To calculate the cost of a path, OSPF uses the following formula:

Cost = Reference bandwidth / Interface bandwidth

The reference bandwidth is a value that represents the theoretical maximum bandwidth of a network. By default, OSPF uses a reference bandwidth of 100 Mbps. However, this value can be changed with the auto-cost reference-bandwidth command.

The interface bandwidth is the actual bandwidth of the outgoing interface that connects to the next hop towards the destination network. OSPF uses the bandwidth command to determine the bandwidth of an interface.

Once OSPF calculates the cost of all the paths to the destination network, it selects the path with the lowest cost as the preferred path. If there are multiple paths with the same lowest cost, OSPF can load balance traffic across the paths.

Therefore, the answer that correctly explains how OSPF selects a route when learning multiple paths to a network is C. OSPF divides a reference bandwidth of 100 Mbps by the actual bandwidth of the outgoing interface to calculate the route with the lowest cost.