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):  

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.  

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Actual exam question from Cisco's 200-301 Exam.

Sample Questions for Cisco 200-301 Exam Prep Practice Tests

Which of the following should be included in an effective Cisco 200-301 study plan?

A. Memorizing all Cisco router models

B. Practicing subnetting, configuring devices, and reviewing exam objectives regularly

C. Skipping hands-on labs to save time

D. Focusing only on theory and avoiding practice exams