During a network audit, an administrator inspects a server configured with the static IPv4… — CompTIA A+ (Core 1 & Core 2)

During a network audit, an administrator inspects a server configured with the static IPv4 address $172.20.12.85/22$ (subnet mask $255.255.252.0$ ). The host can successfully communicate with local devices on its subnet but cannot reach any external networks. Command output confirms the default gateway is set to $172.20.16.1$ and the DNS server is set to $172.20.12.2$ .

Which of the following statements correctly explain the root cause of the routing failure and how to resolve it? (Select TWO.)

The configured default gateway resides outside the server's valid local subnet range of $172.20.12.1$ through $172.20.15.254$ .Answer
B
The DNS server address must be updated to $172.20.16.1$ because DNS services can only be hosted on the router designated as the default gateway.
The default gateway must be reconfigured to an IP address within the $172.20.12.0/22$ network address space.Answer
D
The server must be reconfigured to automatically request an APIPA address starting with $169.254$ to enable routing to remote subnets.

Answer

The default gateway is misconfigured on a different subnet outside the local range of

172.20.12.1

172.20.15.254

, and it must be changed to an IP address within the local

172.20.12.0/22

network space.

With a CIDR notation of /22 (

255.255.252.0

), the network block size in the third octet is 4. The subnet housing host

172.20.12.85

starts at

172.20.12.0

and ends at broadcast address

172.20.15.255

, making the valid host range

172.20.12.1

through

172.20.15.254

. The configured gateway

172.20.16.1

is on a separate subnet. A default gateway must reside on the local subnet to process off-subnet packets.

Step-by-Step Solution

Calculate the subnet boundary for

172.20.12.85/22

A /22 prefix corresponds to

255.255.252.0

. The block size in the third octet is

256 - 252 = 4

. Subnet ranges increment by 4 starting from 0:

0-3

4-7

8-11

12-15

. Thus, the local subnet is

172.20.12.0/22

, spanning usable host IPs from

172.20.12.1

172.20.15.254

Determining the network boundary reveals which IP addresses are local to the server.

Evaluate the current default gateway address (

172.20.16.1

The gateway

172.20.16.1

belongs to the adjacent network (

172.20.16.0/22

) and is not on the local

172.20.12.0/22

subnet.

A host cannot communicate directly with a default gateway that does not share its local layer 3 subnet.

Identify the required corrective configuration.

The default gateway must be updated to a valid router interface IP located within the local

172.20.12.0/22

network.

This allows the host to direct off-subnet traffic to its local router interface for forwarding.

Key Concept

Subnet Mask Calculation and Default Gateway Alignment

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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