The answer is that no port conflict occurs because the translations are extended entries, meaning the router tracks the full five-tuple—protocol, inside global IP, inside global port, outside global IP, and outside global port—to keep each session unique. Even when multiple internal hosts share the same inside global port 1024, the combination of different outside global IPs and ports (like 198.51.100.10:53 or 203.0.113.100:443) ensures each translation is distinct. On the CCNA 200-301 v2 exam, this concept tests your understanding of how PAT with extended entries allows port reuse without conflict, a common trap where students assume a shared inside global port must cause a collision. The key is that PAT does not rely solely on the inside global port for uniqueness; it uses the destination address and port as well. Memory tip: think of it as a “five-finger handshake”—each finger (protocol, source IP, source port, dest IP, dest port) must match for a conflict, so sharing just one finger is harmless.
CCNA Network Services and Security Practice Question
This 200-301 practice question tests your understanding of network services and security. 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 nat translations verbose
Pro Inside global Inside local Outside local Outside global
--- 203.0.113.5 10.1.1.0/24 --- ---
udp 203.0.113.5:1024 10.1.1.10:5000 198.51.100.10:53 198.51.100.10:53
create 00:03:45, use 00:00:10 timeout: 300000, flags: extended
dynamic, mapping-id: 2
udp 203.0.113.5:1024 10.1.1.11:5001 198.51.100.10:53 198.51.100.10:53
create 00:03:45, use 00:00:10 timeout: 300000, flags: extended
dynamic, mapping-id: 2
tcp 203.0.113.5:1024 10.1.1.12:34567 203.0.113.100:443 203.0.113.100:443
create 00:01:22, use 00:00:05 timeout: 86400, flags: extended
dynamic, mapping-id: 2
tcp 203.0.113.5:1024 10.1.1.13:45678 203.0.113.200:22 203.0.113.200:22
create 00:00:55, use 00:00:03 timeout: 86400, flags: extended
dynamic, mapping-id: 2
Refer to the exhibit. A network administrator configures NAT overload on R1 to allow internal hosts in the 10.1.1.0/24 subnet to access the Internet. After the configuration, the administrator runs the show ip nat translations verbose command and notices that several internal sessions all appear to use the same inside global port 1024. The administrator is concerned that port conflicts will occur. Based on the output, which statement is correct?
R1# show ip nat translations verbose
Pro Inside global Inside local Outside local Outside global
--- 203.0.113.5 10.1.1.0/24 --- ---
udp 203.0.113.5:1024 10.1.1.10:5000 198.51.100.10:53 198.51.100.10:53
create 00:03:45, use 00:00:10 timeout: 300000, flags: extended
dynamic, mapping-id: 2
udp 203.0.113.5:1024 10.1.1.11:5001 198.51.100.10:53 198.51.100.10:53
create 00:03:45, use 00:00:10 timeout: 300000, flags: extended
dynamic, mapping-id: 2
tcp 203.0.113.5:1024 10.1.1.12:34567 203.0.113.100:443 203.0.113.100:443
create 00:01:22, use 00:00:05 timeout: 86400, flags: extended
dynamic, mapping-id: 2
tcp 203.0.113.5:1024 10.1.1.13:45678 203.0.113.200:22 203.0.113.200:22
create 00:00:55, use 00:00:03 timeout: 86400, flags: extended
dynamic, mapping-id: 2
A
The NAT configuration is missing the overload keyword, causing all internal hosts to share a single source port.
Why wrong: Missing the overload keyword would result in dynamic NAT that maps one inside local address to one inside global address at a time, not PAT that reuses ports. In that case, the translations would not have the 'extended' flag and would show only one inside local address per global address. The exhibit shows multiple inside local addresses all mapped to the same global IP with a port, which is classic PAT, indicating overload is configured.
B
The static NAT entry mapping 203.0.113.5 to the entire 10.1.1.0/24 subnet forces all subordinate translations to use the same port 1024.
Why wrong: The line '--- 203.0.113.5 10.1.1.0/24 --- ---' is not a static NAT configuration; it is a summary line that indicates the inside global IP assigned to the 10.1.1.0/24 subnet for dynamic translations. It does not force a specific port. The dynamic entries below show the actual PAT translations.
C
The dynamic NAT pool is exhausted, forcing the router to reuse port 1024 for all new sessions.
Why wrong: If the pool were exhausted, the router would either refuse new translations or reuse a global address, but PAT would still assign different source ports. The exhibit shows four concurrent translations all using the same global port, which indicates that the router is differentiating sessions by destination, not that the pool is exhausted.
D
The translations are extended entries, so the combination of inside global IP, outside global IP, and port ensures each session is unique, even though the inside global port is the same.
Each table entry carries the 'extended' flag, which means the translation includes the destination address and port. This allows the same inside global port 1024 to be used simultaneously for different destinations (198.51.100.10:53, 203.0.113.100:443, 203.0.113.200:22). The five‑tuple still uniquely identifies the session, so port conflicts do not occur.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The translations are extended entries, so the combination of inside global IP, outside global IP, and port ensures each session is unique, even though the inside global port is the same.
The exhibit shows four dynamic NAT translations, each marked with the 'extended' flag. In extended PAT, the translation table includes the destination IP address and port (the Outside global field). Even though all entries share the same inside global port 1024, each translation has a different Outside global pair (198.51.100.10:53 for UDP, 203.0.113.100:443 and 203.0.113.200:22 for TCP). Therefore, the five‑tuple (protocol, inside global IP, inside global port, outside global IP, outside global port) remains unique for each session, and no port conflict exists. The 'extended' flag explicitly confirms that the router is using this extended matching logic to allow port reuse.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The NAT configuration is missing the overload keyword, causing all internal hosts to share a single source port.
Why it's wrong here
Missing the overload keyword would result in dynamic NAT that maps one inside local address to one inside global address at a time, not PAT that reuses ports. In that case, the translations would not have the 'extended' flag and would show only one inside local address per global address. The exhibit shows multiple inside local addresses all mapped to the same global IP with a port, which is classic PAT, indicating overload is configured.
✗
The static NAT entry mapping 203.0.113.5 to the entire 10.1.1.0/24 subnet forces all subordinate translations to use the same port 1024.
Why it's wrong here
The line '--- 203.0.113.5 10.1.1.0/24 --- ---' is not a static NAT configuration; it is a summary line that indicates the inside global IP assigned to the 10.1.1.0/24 subnet for dynamic translations. It does not force a specific port. The dynamic entries below show the actual PAT translations.
✗
The dynamic NAT pool is exhausted, forcing the router to reuse port 1024 for all new sessions.
Why it's wrong here
If the pool were exhausted, the router would either refuse new translations or reuse a global address, but PAT would still assign different source ports. The exhibit shows four concurrent translations all using the same global port, which indicates that the router is differentiating sessions by destination, not that the pool is exhausted.
✓
The translations are extended entries, so the combination of inside global IP, outside global IP, and port ensures each session is unique, even though the inside global port is the same.
Why this is correct
Each table entry carries the 'extended' flag, which means the translation includes the destination address and port. This allows the same inside global port 1024 to be used simultaneously for different destinations (198.51.100.10:53, 203.0.113.100:443, 203.0.113.200:22). The five‑tuple still uniquely identifies the session, so port conflicts do not occur.
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓The translations are extended entries, so the combination of inside global IP, outside global IP, and port ensures each session is unique, even though the inside global port is the same.Correct answer▾
Why this is correct
Each table entry carries the 'extended' flag, which means the translation includes the destination address and port. This allows the same inside global port 1024 to be used simultaneously for different destinations (198.51.100.10:53, 203.0.113.100:443, 203.0.113.200:22). The five‑tuple still uniquely identifies the session, so port conflicts do not occur.
✗The NAT configuration is missing the overload keyword, causing all internal hosts to share a single source port.Wrong answer — click to see why▾
Why this is wrong here
Candidates think that seeing the same global port means overload is not operating, but port reuse is normal in extended PAT.
✗The static NAT entry mapping 203.0.113.5 to the entire 10.1.1.0/24 subnet forces all subordinate translations to use the same port 1024.Wrong answer — click to see why▾
Why this is wrong here
Candidates may misinterpret the summary line as a static identity NAT rule that locks all translations to a single port.
✗The dynamic NAT pool is exhausted, forcing the router to reuse port 1024 for all new sessions.Wrong answer — click to see why▾
Why this is wrong here
Candidates confuse pool exhaustion (no free global addresses) with port reuse. Exhaustion typically manifests as translation failures, not as many entries sharing the same port.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Trap categories for this question
Keyword trap
Missing the overload keyword would result in dynamic NAT that maps one inside local address to one inside global address at a time, not PAT that reuses ports. In that case, the translations would not have the 'extended' flag and would show only one inside local address per global address. The exhibit shows multiple inside local addresses all mapped to the same global IP with a port, which is classic PAT, indicating overload is configured.
Command / output trap
Missing the overload keyword would result in dynamic NAT that maps one inside local address to one inside global address at a time, not PAT that reuses ports. In that case, the translations would not have the 'extended' flag and would show only one inside local address per global address. The exhibit shows multiple inside local addresses all mapped to the same global IP with a port, which is classic PAT, indicating overload is configured.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 200-301 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
Network Services and Security — This question tests Network Services and Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The translations are extended entries, so the combination of inside global IP, outside global IP, and port ensures each session is unique, even though the inside global port is the same. — The exhibit shows four dynamic NAT translations, each marked with the 'extended' flag. In extended PAT, the translation table includes the destination IP address and port (the Outside global field). Even though all entries share the same inside global port 1024, each translation has a different Outside global pair (198.51.100.10:53 for UDP, 203.0.113.100:443 and 203.0.113.200:22 for TCP). Therefore, the five‑tuple (protocol, inside global IP, inside global port, outside global IP, outside global port) remains unique for each session, and no port conflict exists. The 'extended' flag explicitly confirms that the router is using this extended matching logic to allow port reuse.
What should I do if I get this 200-301 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 200-301 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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