What is the problem?

You are the Cisco administrator for Verigon Incorporated. The given exhibit displays some of the devices in the network. (Click the Exhibit(s) button.) Workstation A
can communicate with Workstation C but cannot communicate with Workstation B.
What is the problem?

A.
Workstation B has an incorrect default gateway

B.
Workstation A has an incorrect subnet mask

C.
Workstation A has an incorrect default gateway

D.
Workstation B has an incorrect subnet mask

Explanation:
Workstation A has an incorrect default gateway. To communicate with remote computers or those computers outside of its own subnet, a computer must have the
address of the nearest router interface as its default gateway. In this case, the default gateway of Workstation A should be 192.168.10.5/24, which is the Serial0
address of Router A. The diagram shows that it is instead configured as 192.168.10.4/24. This will not cause a problem for Workstation A to communicate with
Workstation C, but it will make communication with remote subnets impossible.
Workstation B does not have an incorrect default gateway. Its nearest router interface is 10.0.0.1/8, which is the configuration of its default gateway.
Workstation A does not have an incorrect subnet mask. The mask used by Workstation C and the router interface of Router A, which are in the same subnet, is /24,
or 255.255.255.0, which is also the subnet mask used by Workstation A.
Workstation B does not have an incorrect subnet mask. Since the subnet mask of the router interface that is nearest to Workstation B is /8, or 255.0.0.0, then
Workstation B also should have an 8-bit mask.
Objective:
Routing Fundamentals
Sub-Objective:
Troubleshoot basic Layer 3 end-to-end connectivity issues

Cisco > Technology Support > IP > IP Routing > Design Technotes > IP Addressing and Subnetting for New Users > Document ID: 13788 > Understanding IP
Addresses
Cisco > Technology Support > IP > IP Addressing Services > Design Technotes > Subnet Zero and the All-Ones Subnet > Document ID: 13711
CCNA ICND2 Official Exam Certification Guide (Cisco Press, ISBN 1-58720-181-X), Appendices D, E and H: Subnetting.