mediumMultiple ChoiceObjective-mapped
Resolving NAT Hairpinning Issues on Cisco ASA for Internal Access
Exhibit
configure terminal access-list OUTSIDE extended permit tcp any host 203.0.113.10 eq www access-list OUTSIDE extended permit udp any host 203.0.113.10 eq domain nat (inside,outside) source dynamic any interface
Refer to the exhibit. An ASA is configured with the above access-list and NAT rule. A web server is reachable from the internet via the public IP 203.0.113.10. However, internal users from the inside network cannot access the web server using its public IP address. What is the most likely cause?
Quick Answer
The answer is a missing static NAT configuration for the server. This is the most likely cause because NAT hairpinning on a Cisco ASA requires a bidirectional mapping—typically created with the `static` keyword—so that internal traffic destined to the public IP 203.0.113.10 is correctly translated back to the server’s private IP 192.168.1.10. Without this explicit static NAT, the ASA sees the source IP as internal and the destination as the outside interface’s public IP, but lacks the necessary reverse translation, causing the packet to be dropped or misrouted. On the Cisco SCOR / CCNP Security Core 350-701 exam, this scenario tests your understanding of NAT hairpinning and the difference between one-way and two-way NAT translations. A common trap is assuming that a standard static NAT rule automatically handles internal-to-public traffic, but in reality, the `static` keyword must be applied to the NAT statement to enable the bidirectional flow. Memory tip: think “static for symmetric” — if traffic must return through the same path, the NAT rule must be explicitly bidirectional.
⚠ Common exam trap
Candidates often assume a single static NAT rule automatically handles all traffic directions, but Cisco tests the nuance that internal-to-internal traffic via the public IP requires explicit NAT configuration (often called 'NAT reflection' or 'hairpinning'), which is not implied by a basic static NAT.
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 NAT rule is missing a static NAT for the server.
The NAT rule shown is a static NAT for the web server, but it is missing the 'static' keyword or the bidirectional mapping required for internal users to reach the server using its public IP. Without a proper static NAT (e.g., 'nat (inside,outside) static 192.168.1.10 service tcp www www'), the ASA does not translate the source IP of internal traffic destined to 203.0.113.10 back to the server's private IP, causing the traffic to be dropped or misrouted.
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 rule is missing a static NAT for the server.
Why this is correct
Without a static NAT, internal users cannot access the server via the public IP due to lack of hairpinning.
- ✗
The access-list does not permit traffic from inside to outside for that destination.
Why it's wrong here
The ACL is applied on the outside interface, so it does not filter inside-to-outside traffic.
- ✗
The interface ACL is applied inbound on the inside interface.
Why it's wrong here
The ACL is applied to the outside interface, not inside.
- ✗
The default route is missing.
Why it's wrong here
A missing default route would affect traffic to the internet, but not specifically internal access to a public IP.
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Same concept, more angles
1 more way this is tested on 350-701
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Refer to the exhibit. A host with IP address 10.0.0.5 sends traffic to destination 192.168.2.10. The traffic is not being translated. What is the most likely cause?
medium- A.The security-level of the inside interface is too high to allow NAT.
- ✓ B.The ACL INSIDE_NAT does not permit traffic to the destination network 192.168.2.0/24.
- C.The interface outside does not have a valid IP address assigned.
- D.The NAT statement uses source dynamic instead of source static; dynamic cannot translate internal IPs.
Why B: The access-list INSIDE_NAT permits traffic to network 192.168.3.0/24, but the destination is 192.168.2.10, which is not matched. Therefore, NAT is not applied to that traffic. Option B is correct. Options A, C, and D are not relevant because dynamic NAT is allowed, outside interface has an IP, and security-level does not affect NAT.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-701 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-701 exam.