Question 1hardmultiple choice
Full question →hardmultiple choiceObjective-mapped
Exhibit
interface g0/0 ip address 192.168.20.1 255.255.255.0 ip nat outside ! interface g0/1 ip address 203.0.113.2 255.255.255.252 ip nat inside ! ip nat inside source list 10 interface g0/1 overload access-list 10 permit 192.168.20.0 0.0.0.255
Exhibit: Hosts in VLAN 20 must reach the internet through PAT, but users report no external connectivity. Which configuration issue best explains the problem?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
The ACL should deny 192.168.20.0/24 instead of permit it
The NAT ACL must normally permit the inside local addresses that will be translated.
B
Best answer
The interfaces are marked with inside and outside in the wrong places
Reversed NAT roles stop the expected translations.
C
Distractor review
PAT cannot be used with a /30 WAN link
A /30 WAN link is common for PAT deployments.
D
Distractor review
NAT overload requires a route-map instead of an ACL
A route-map can be used, but a standard ACL is valid.
Common exam trap
Common exam trap: answer the scenario, not the keyword
A frequent exam trap is assuming that the ACL or the subnet mask is the cause of NAT failure when the real issue is reversed inside and outside interface roles. Candidates often overlook the importance of interface designation commands (ip nat inside and ip nat outside), which are crucial for NAT operation. Without correct interface roles, the router cannot translate addresses properly, causing hosts to lose external connectivity even if ACLs and routing are correct. This trap is tempting because ACLs and subnetting are more familiar concepts, but interface roles are equally critical for NAT to function.
Technical deep dive
How to think about this question
Network Address Translation (NAT) is a fundamental technology that allows private IP addresses within a VLAN, such as VLAN 20, to communicate with external networks by translating these private addresses into public IP addresses. PAT, a form of NAT overload, enables multiple devices to share a single public IP by differentiating connections using unique source port numbers. This process depends heavily on the router correctly identifying which interfaces are 'inside' (connected to the private network) and which are 'outside' (connected to the public network). The NAT configuration requires explicit commands to mark interfaces as inside or outside. The router uses these designations to determine the direction of translation. If these roles are reversed, the router attempts to translate addresses in the wrong direction, causing translation failures and loss of connectivity. Even if the ACL correctly permits the inside local subnet and the routing is correct, reversed interface roles will prevent NAT from functioning properly. A common exam trap involves confusing the inside and outside interface commands, leading to NAT not translating packets as expected. In practical networking, this misconfiguration results in hosts being unable to access the internet despite seemingly correct ACLs and routing. Understanding the role of interface designations in NAT is critical for troubleshooting and configuring PAT in Cisco environments, especially for VLAN-based internal networks requiring internet access.
KKey Concepts to Remember
- NAT (Network Address Translation) requires correct identification of inside and outside interfaces to translate private IP addresses to public IP addresses properly.
- PAT (Port Address Translation) allows multiple hosts in a private VLAN to share a single public IP address by translating source ports uniquely.
- An ACL (Access Control List) used in NAT must permit the inside local IP address range to enable translation of those addresses to outside global addresses.
- Reversing the inside and outside interface designations in NAT configuration prevents the router from performing the expected address translations.
- A /30 WAN link does not restrict the use of PAT; it is commonly used in point-to-point links supporting NAT overload.
- NAT overload can be configured using either a standard ACL or a route-map to define which inside addresses are translated.
- Correct NAT configuration ensures that hosts in VLAN 20 can reach external networks by translating their private IP addresses to a routable public IP.
- Misconfiguration of NAT interface roles is a common cause of no external connectivity despite correct ACL and routing.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
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More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
Question 1
A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?
Question 2
A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?
Question 3
What is the OSPF metric called?
Question 4
A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?
Question 5
A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?
Question 6
A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?
FAQ
Questions learners often ask
What does this 200-301 question test?
NAT (Network Address Translation) requires correct identification of inside and outside interfaces to translate private IP addresses to public IP addresses properly.
What is the correct answer to this question?
The correct answer is: The interfaces are marked with inside and outside in the wrong places — NAT overload works only when the inside and outside interfaces are identified correctly. Here the roles are reversed, so translations are not built in the right direction.
What should I do if I get this 200-301 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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