Question
An enterprise is trying to limit outbound DNS traffic originating from its internal network. Outbound DNS requests will only be allowed from one device with the IP address 10.50.10.25. Which of the following firewall ACLs will accomplish this goal?
- A. Access list outbound permit 0.0.0.0/0 0.0.0.0/0 port 53 Access list outbound deny 10.50.10.25/32 0.0.0.0/0 port 53
- B. Access list outbound permit 0.0.0.0/0 10.50.10.25/32 port 53 Access list outbound deny 0.0.0.0/0 0.0.0.0/0 port 53
- C. Access list outbound permit 0.0.0.0/0 0.0.0.0/0 port 53 Access list outbound deny 0.0.0.0/0 10.50.10.25/32 port 53
- D. Access list outbound permit 10.50.10.25/32 0.0.0.0/0 port 53 Access list outbound deny 0.0.0.0/0 0.0.0.0/0 port 53 Correct
Explanation
Each rule lists the source first and the destination second, and the firewall evaluates rules from the top. Option D first permits DNS (port 53) from the single host 10.50.10.25/32 to any destination, then denies DNS from every other source. Options A and C permit all DNS traffic in their first rule, so the deny that follows never takes effect, and option B uses 10.50.10.25 as the destination instead of the source.
