You use OSPF as your network routing protocol. You use the command show ip route and you
see several routes described as 0, 0 IA, 0 E1, and 0 E2. What routes are in your area?

A.
OIA

B.
OE1

C.
O E2

D.
0

Explanation:
Depending on the point where a network is sourced, there are various types of routes that could
be present in an OSPF domain. When there are multiple routes to a particular network in a OSPF
domain, the type of the route influences the route that is selected and installed by the router in the
routing table. In OSPF, routes that are learned by a router from OSPF sources within the same
area are known as intra-area routes. Routes that originate from an OSPF router in a different area
are considered as inter-area routes. Certain networks could belong to a domain outside OSPF,
which could then be redistributed into the OSPF by an Autonomous System
Boundary Router (ASBR). Such routes are considered external routes. They can be further divided
into external type-1 or external type-2 routes, depending on how they are advertised while being
redistributing on the ASBR. The difference between these two types is the way in which the metric
for the route is calculated.
OSPF-running routers use these criteria to select the best route to be installed in the routing table:
1. Intra-area routes.
2. Inter-area routes.

3. External Type-1 routes.
4. External Type-2 routes.
a. If there are multiple routes to a network with the same route type, the OSPF metric calculated
as cost based on the bandwidth is used for selecting the best route. The route with the lowest
value for cost is chosen as the best route.
b. If there are multiple routes to a network with the same route type and cost, it chooses all the
routes to be installed in the routing table, and the router does equal cost load balancing across
multiple paths.