Exam 300-101 topic 1 question 31 discussion

SIMULATION -
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 New York
S0/1 192.168.16.6/30 "" Link between Seattle and Chicago

Secret Password: cisco -

New York -
S0/1 192.168.54.10/30 "" Link between Chicago and New York

Loopback0 172.16.189.189 -

Secret Password: cisco -





See explanation below -

Suggested Answer: 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 4thoctet of the Network Address:

The 4thoctet 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 -
Let's find the wildcard mask of /30.
Subnet Mask: (Network Bits "" 1's, Host Bits "" 0's)
Let's 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 ospf10 -
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. There fore 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.