A network administrator recently redistributed RIP routes into an OSPF domain. However, the
administrator wants to configure the network so that instead of 32 external type-5 LSAs flooding
into the OSPF network, there is only one.

What must the administrator do to accomplish this?

A.
Configure summarization on R1 with area 1 range 172.16.32.0 255.255.224.0

B.
Configure summarization on R1 with summary-address 172.16.32.0 255.255.224.0

C.
Configure area 1 as a stub area with area 1 stub

D.
Configure area 1 as a NSSA area with area 1 stub nssa

Explanation:
In many cases, the router doesn’t even need specific routes to each and every subnet (for
example, 172.16.1.0/24). It would be just as happy if it knew how to get to the major network (for
example, 172.16.0.0/16) and let another router take it from there. In our telephone network
example, the local telephone switch should only need to know to route a phone call to the switch
for the called area code. Similarly, a router’s ability to take a group of subnetworks and summarize
them as one network (in other words, one advertisement) is called route summarization. Besides
reducing the number of routing entries that a router must keep track of, route summarization can
also help protect an external router from making multiple changes to its routing table due to
instability within a particular subnet. For example, let’s say that we were working on a router that
connected to 172.16.2.0/24. As we were working on the router, we rebooted it several times. If we
were not summarizing our routes, an external router would see each time 172.16.2.0/24 went
away and came back. Each time, it would have to modify its own routing table. However, if our
external router were receiving only a summary route (i.e., 172.16.0.0/16), then it wouldn’t have to
be concerned with our work on one particular subnet. This is especially a problem for EIGRP,
which can create stuck in active (SIA) routes that can lead to a network melt-down.
Summarization Example We have the following networks that we want to advertise as a single

summary route: * 172.16.100.0/24 * 172.16.101.0/24 * 172.16.102.0/24 * 172.16.103.0/24 *
172.16.104.0/24 * 172.16.105.0/24 * 172.16.106.0/24