Route.com is a small IT corporation that is attempting to implement the network shown in the exhibit.

CORRECT TEXT
Route.com is a small IT corporation that is attempting to implement the network shown in the
exhibit. Currently the implementation is partially completed. OSPF has been configured on routers
Chicago and NewYork. The SO/O interface on Chicago and the SO/1 interface on NewYork are in
Area 0. The loopbackO interface on NewYork is in Area 1. However, they cannot ping from the
serial interface of the Seattle router to the loopback interface of the NewYork router. You have
been asked to complete the implementation to allow this ping.
ROUTE.com’s corporate implementation guidelines require:
• The OSPF process ID for all routers must be 10.
• The routing protocol for each interface must be enabled under the routing process.
• The routing protocol must be enabled for each interface using the most specific wildcard mask
possible.
•The serial link between Seattle and Chicago must be in OSPF area 21.
•OSPF area 21 must not receive any inter-area or external routes.
Network Information
Seattle
S0/0 192.168.16.5/30 – Link between Seattle and Chicago
Secret Password: cisco
Chicago
S0/0 192.168.54.9/30 – Link between Chicago and NewYork

S0/1 192.168.16.6/30 – Link between Seattle and Chicago Secre
Password: cisco
NewYork
S0/1 192.168.54.10/30 – Link between Chicago and NewYork
Loopback0 172.16.189.189
Secret Password: cisco

Answer: See the explanation

Explanation:
Note: In actual exam, the IP addressing, OSPF areas and process ID, and router hostnames may
change, but the overall solution is the same.
Seattle’s S0/0 IP Address is 192.168.16.5/30. So, we need to find the network address and
wildcard mask of 192.168.16.5/30 in order to configure the OSPF.

IP Address: 192.168.16.5 /30
Subnet Mask: 255.255.255.252
Here subtract 252 from 2565, 256-252 = 4, hence the subnets will increment by 4.
First, find the 4th octet of the Network Address:

The 4th octet of IP address (192.168.16.5) belongs to subnet 1 (4 to 7).
Network Address: 192.168.16.4
Broadcast Address: 192.168.16.7
Lets find the wildcard mask of /30.
Subnet Mask: (Network Bits – 1’s, Host Bits – 0’s)
Lets find the wildcard mask of /30:

Now we configure OSPF using process ID 10 (note the process ID may change to something else
in real exam).

Seattle>enable
Password:
Seattle#conf t
Seattle(config)#router ospf 10
Seattle(config-router)#network 192.168.16.4 0.0.0.3 area 21
One of the tasks states that area 21 should not receive any external or inter-area routes (except
the default route).
Seattle(config-router)#area 21 stub
Seattle(config-router)#end
Seattle#copy run start
Chicago Configuration:
Chicago>enable
Password: cisco
Chicago#conf t
Chicago(config)#router ospf 10
We need to add Chicago’s S0/1 interface to Area 21
Chicago(config-router)#network 192.168.16.4 0.0.0.3 area 21
Again, area 21 should not receive any external or inter-area routes (except the default route).
In order to accomplish this, we must stop LSA Type 5 if we don’t want to send external routes. And
if we don’t want to send inter-area routes, we have to stop LSA Type 3 and Type 4. Therefore we
want to configure area 21 as a totally stubby area.
Chicago(config-router)#area 21 stub no-summary
Chicago(config-router)#end
Chicago#copy run start
The other interface on the Chicago router is already configured correctly in this scenario, as well
as the New York router so there is nothing that needs to be done on that router.

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