What Wild Card Mask Will Match Networks 172.16.0.0 Through 172.19.0.0?

well-structured Cisco 200-301 study plan is essential for anyone aiming to pass the CCNA certification exam. This plan should cover all core topics outlined in the Cisco 200-301 exam blueprint, including network fundamentals, IP connectivity, security fundamentals, automation, and more

Tech Professionals

07 April 2025

Cisco

What Wild Card Mask Will Match Networks 172.16.0.0 Through 172.19.0.0?

Introduction To Cisco 200-301 Study plan

Preparing for the Cisco CCNA 200 301 exam requires a solid understanding of networking concepts, including wild card masks in Access Control Lists (ACLs). A common question that arises is:

What wild card mask will match networks 172.16.0.0 through 172.19.0.0?

In this comprehensive guide, we’ll break down the solution while integrating a structured Cisco 200-301 study plan to help you master this topic and ace your exam.

Understanding Wild Card Masks

Before solving the problem, let’s clarify what a wild card mask is and how it differs from a subnet mask.

1. What is a Wild Card Mask?

Used in ACLs (Access Control Lists) and OSPF configurations.
Determines which bits in an IP address must match (0 = must match, 1 = ignore).
Example: A wild card mask of 0.0.0.255 means the first three octets must match, but the last octet can vary.

2. Wild Card Mask vs. Subnet Mask

Subnet Mask Wild Card Mask
Defines network and host portions (1s = network, 0s = host) Defines which bits to check (0s = check, 1s = ignore)

Example: 255.255.255.0 Example: 0.0.0.255

Solving the Problem: Matching 172.16.0.0 – 172.19.0.0

To match networks 172.16.0.0 through 172.19.0.0, we need a wild card mask that allows the third octet to range from 16 to 19 while keeping the rest fixed.

Step 1: Convert IP Ranges to Binary

Let’s analyze the third octet (since the first two octets are 172.* and the last is 0.0):

Network	Third Octet (Decimal)	Third Octet (Binary)
172.16.0.0	16	0001 0000
172.17.0.0	17	0001 0001
172.18.0.0	18	0001 0010
172.19.0.0	19	0001 0011

Step 2: Find the Common Bits

Looking at the binary, the first 4 bits (0001) remain the same, while the last 4 bits change.
Fixed bits (must match): `0001` (first 4 bits)
Variable bits (can change): `xxxx` (last 4 bits)

Step 3: Determine the Wild Card Mask

A 0 in the wild card mask means must match.

A 1 means can vary.
For the third octet:
First 4 bits = must match (0)
Last 4 bits = can vary (1)
Thus, the wild card mask for the third octet is:
`0000 1111` = 15 in decimal.
Final Wild Card Mask

Since the first two octets (172.*) must match exactly, and the last octet (0.0) must also match:

IP Address: `172.16.0.0`
Wild Card Mask: `0.3.0.0`

Explanation:

First Octet (172): `0` (must match exactly)
Second Octet (16-19): `3` (binary `0000 0011`, allows variation in last 4 bits)
Third & Fourth Octets (0.0): `0.0` (must match exactly)

Verification

Let’s test if this wild card mask works:
`172.16.0.0` & `0.3.0.0` → Matches 172.16.0.0 – 172.19.0.0
`172.20.0.0` → Does not match (since 20 is `0001 0100`, differing beyond the mask).
Cisco 200-301 Study Plan: Mastering Wild Card Masks

To ensure you fully grasp wild card masks for the CCNA 200-301 Certification, follow this structured study plan:

Week 1: Networking Fundamentals

Review IPv4 addressing & subnetting.
Practice converting decimal to binary.
Understand ACLs and OSPF basics.

Week 2: Wild Card Mask Deep Dive

Solve 10+ wild card mask problems (like the one above).
Compare subnet masks vs. wild card masks.
Use Cisco Packet Tracer to test ACL configurations.

Week 3: Practice & Labs

Set up ACLs in a lab environment.
Experiment with different wild card masks to see their effects.
Take CCNA practice tests focusing on ACLs.

Week 4: Exam Readiness

Review common CCNA wild card mask questions.
Join study groups (like Study4Pass forums).
Take full-length mock exams.

Conclusion

Understanding wild card masks is crucial for the Cisco 200-301 exam, especially for ACL configurations. By following the Cisco 200-301 study plan outlined here, you’ll gain confidence in tackling such questions.