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CISA Practice Question: Refer to the exhibit

Exhibit

Refer to the exhibit.

```
! Cisco ASA configuration snippet
access-list OUTSIDE_IN extended permit tcp any host 203.0.113.10 eq www
access-list OUTSIDE_IN extended permit tcp any host 203.0.113.10 eq https
access-list OUTSIDE_IN extended deny ip any any log
!
object network WEB_SERVER
 host 203.0.113.10
nat (inside,outside) source static any any destination static WEB_SERVER WEB_SERVER no-proxy-arp route-lookup
!
```

Refer to the exhibit. A security administrator is troubleshooting why external users cannot reach the web server at 203.0.113.10 from the internet. Based on the configuration, what is the MOST likely issue?

⚠ Common exam trap

Many exam-takers assume a NAT rule alone is sufficient for inbound traffic, overlooking the Layer 2 requirement that the ASA must respond to ARP for the public IP via proxy ARP.

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 'no-proxy-arp' option prevents the ASA from responding to ARP requests for the public IP

The 'no-proxy-arp' command disables proxy ARP on the ASA interface for the public IP address 203.0.113.10. Without proxy ARP, the ASA will not respond to ARP requests from upstream routers for that IP, so traffic destined to the web server is never delivered to the ASA for NAT processing. This is the most likely cause because the NAT rule exists but the ASA cannot intercept the traffic at Layer 2.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • No NAT rule is configured for the web server

    Why it's wrong here

    A NAT rule exists.

  • The 'no-proxy-arp' option prevents the ASA from responding to ARP requests for the public IP

    Why this is correct

    Without proxy ARP, the ASA does not claim the public IP, so traffic is not received.

  • The source address is not translated

    Why it's wrong here

    Source translation is not required for inbound traffic; destination translation is the issue.

  • The access list denies incoming web traffic

    Why it's wrong here

    The ACL permits tcp to port 80 and 443.

Visual reference

Inside (Private) PC-A 10.0.0.1 PC-B 10.0.0.2 NAT Router Outside (Public) 203.0.113.1 Inside Global Server PAT: many private IPs share one public IP via unique port numbers

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JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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