The network associate is configuring OSPF on the Core router shown below. All the connections to the branches should be participating in OSPF. The link to the ISP should NOT participate in OSPF and should only be advertised as the default route. What set of commands will properly configure the Core router?

The network associate is configuring OSPF on the Core router shown below:

A. Core(config-router)# default-information originate
Core(config-router)# network 10.0.0.00.255.255.255 area 0
Core(config-router)# exit
Core(config)# ip route 0.0.0.00.0.0.010.10.2.14
B. Core(config-router)# default-information originate
Core(config-router)# network 10.10.2.32 0.0.0.31 area 0
Core(config-router)# exit
Core(config)# ip route 0.0.0.00.0.0.0 10.10.2.14
C. Core(config-router)# default-information originate
Core(config-router)# network 10.10.2.13 0.0.0.242 area 0
Core(config-router)# exit
Core(config)# ip route 0.0.0.00.0.0.010.10.2.14
D. Core(config-router)# default-information originate
Core(config-router)# network 10.10.2.16 0.0.0.15 area 0
Core(config-router)# exit
Core(config)# ip route 0.0.0.00.0.0.010.10.2.14

Answer: D

Explanation:

There are two ways to inject a default route into a normal area.
1. If the ASBR already has the default route in its routing table, you can advertise the
existing 0.0.0.0/0 into the OSPF domain with the default-information originate router
configuration command.

2. If the ASBR doesn't have a default route, you can add the keyword always to the
default-information originate command (default-information originate always).

This command will advertise a default route into the OSPF domain, regardless of whether
it has a route to 0.0.0.0. Another benefit of adding always keyword is that it can add
stability to the internetwork. For example, if the ASBR is learning a default route from
another routing domain such as RIP and this route is flapping, then without the always
keyword, each time the route flaps, the ASBR will send a new Type 5 LSA into the OSPF
domain causing some instability inside the OSPF domain. With the always keyword, the
ASBR will advertise the default inside the OSPF domain always, and thus the flapping of
the default route from the RIP domain will not cause any instability inside the OSPF
domain.

In the example shown here, only choice D is correct as the wildcard mask correctly
specifies the 10.10.2.16 0.0.0.15 networks, which include all IP addresses in the
10.10.2.16-10.10.2.31 range.