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300-410 Practice Question: Router R1 is configured with ip nat inside source…
Router R1 is configured with ip nat inside source list 100 interface GigabitEthernet0/1 overload. Internal hosts can access the internet, but traffic to a specific external server at 203.0.113.200 is being dropped. Router R1 shows: show ip nat statistics: Total active translations: 1000. Debug ip nat: NAT: s=192.168.1.1->203.0.113.1, d=203.0.113.200 [0]. The external server shows no received packets. What is the root cause?
⚠ Common exam trap
Cisco often tests the misconception that a successful NAT translation guarantees packet delivery, when in fact the router must still have a valid route to the destination after translation.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The router does not have a route to 203.0.113.200; configure a default route or specific route.
The debug output shows a successful NAT translation from 192.168.1.1 to 203.0.113.1, but the external server at 203.0.113.200 receives no packets. This indicates the router can translate but cannot forward the packet to the destination. Without a route to 203.0.113.200, the router has no next hop for the translated packet, so it is dropped. Configuring a default route or a specific route to 203.0.113.200 resolves the issue.
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 router does not have a route to 203.0.113.200; configure a default route or specific route.
Why this is correct
Without a route, the packet is dropped after NAT.
- ✗
The access-list 100 is blocking the destination.
Why it's wrong here
The ACL is for NAT matching, not for routing.
- ✗
The NAT translation is failing due to port exhaustion.
Why it's wrong here
The debug shows a successful translation, and statistics show only 1000 active translations.
- ✗
The external server is blocking the source IP.
Why it's wrong here
The server shows no received packets, indicating the packet never arrived.
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