200-901 Software Development and Design Practice Question
This 200-901 practice question tests your understanding of software development and design. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
R1# show ip route
Codes: L - local, C - connected, S - static, R - RIP, O - OSPF, B - BGP
D - EIGRP, EX - EIGRP external, N - NAPT
Gateway of last resort is 10.0.0.1
10.0.0.0/8 is variably subnetted, 2 subnets
C 10.0.0.0/24 is directly connected, GigabitEthernet0/0
S 10.0.1.0/24 [1/0] via 10.0.0.2
Refer to the exhibit. A developer is parsing the output of 'show ip route' using Python. Which regular expression would extract the prefix '10.0.1.0/24'?
R1# show ip route
Codes: L - local, C - connected, S - static, R - RIP, O - OSPF, B - BGP
D - EIGRP, EX - EIGRP external, N - NAPT
Gateway of last resort is 10.0.0.1
10.0.0.0/8 is variably subnetted, 2 subnets
C 10.0.0.0/24 is directly connected, GigabitEthernet0/0
S 10.0.1.0/24 [1/0] via 10.0.0.2
A
r'^S\s+(\d+\/\d+)'
Why wrong: Only captures network and mask without dots, e.g., '10/24'.
B
r'^S.*(\d+\.\d+\.\d+\.\d+)'
Why wrong: Captures IP without subnet mask, and .* may skip prefix.
C
r'S\s+(\S+)'
Why wrong: Lacks start anchor and may match other lines with 'S'.
D
r'^S\s+(\d+\.\d+\.\d+\.\d+/\d+)'
Correctly anchors at line start and captures prefix.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
r'^S\s+(\d+\.\d+\.\d+\.\d+/\d+)'
The pattern r'^S\s+(\d+\.\d+\.\d+\.\d+/\d+)' matches a line starting with 'S' followed by whitespace and then the prefix. Option B lacks the start anchor; Option C is too specific; Option D uses greedy matching and may capture extra.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
r'^S\s+(\d+\/\d+)'
Why it's wrong here
Only captures network and mask without dots, e.g., '10/24'.
✗
r'^S.*(\d+\.\d+\.\d+\.\d+)'
Why it's wrong here
Captures IP without subnet mask, and .* may skip prefix.
✗
r'S\s+(\S+)'
Why it's wrong here
Lacks start anchor and may match other lines with 'S'.
✓
r'^S\s+(\d+\.\d+\.\d+\.\d+/\d+)'
Why this is correct
Correctly anchors at line start and captures prefix.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 200-901 NAT questions on configuration and troubleshooting.
Software Development and Design — This question tests Software Development and Design — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: r'^S\s+(\d+\.\d+\.\d+\.\d+/\d+)' — The pattern r'^S\s+(\d+\.\d+\.\d+\.\d+/\d+)' matches a line starting with 'S' followed by whitespace and then the prefix. Option B lacks the start anchor; Option C is too specific; Option D uses greedy matching and may capture extra.
What should I do if I get this 200-901 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related 200-901 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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