Exam PCNSE topic 1 question 327 discussion

A nat : source untrust (any) dest untrust (172.16.15.1) dtrans 192.168.15.47 security : source untrust (any) dest trust (172.16.15.1) application web-browsing The addresses used in destination NAT rules always refer to the original IP address in the packet (that is, the pre-translated address). The destination zone in the NAT rule is determined after the route lookup of the destination IP address in the original packet (that is, the pre-NAT destination IP address). The addresses in the security policy also refer to the IP address in the original packet (that is, the pre-NAT address). However, the destination zone is the zone where the end host is physically connected. In other words, the destination zone in the security rule is determined after the route lookup of the post-NAT destination IP address. https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-admin/networking/nat/nat-configuration-examples/destination-nat-exampleone-to-one-mapping

Analysis: NAT Rule: A incorrectly places the destination zone as Untrust-L3 for the NAT rule. Since the actual server resides in the Trust-L3 zone (192.168.15.47), the NAT rule should translate the destination IP from Untrust-L3 to Trust-L3. B correctly translates the destination IP address 172.16.15.1 (given by DNS) to 192.168.15.47 and sets the destination zone to Trust-L3, where the web server resides. Security Rule: A uses 172.16.15.1 as the destination IP in the security rule. However, after NAT translation, the destination IP will be 192.168.15.47. This mismatch will result in the traffic being denied because the security rule won't match the translated IP. B uses 192.168.15.47 as the destination IP in the security rule, which matches the post-NAT translated IP, ensuring the rule correctly allows the traffic. Conclusion: Option B correctly sets the NAT rule to translate the external IP to the internal IP within the Trust-L3 zone and uses the correct translated IP in the security rule to allow the traffic. This makes B the correct configuration.

Should be B. Nat is always original source zone/ip and original destination zone/ip. Security policy should be original source zone/ip, original IP, and FINAL destination zone.

The anser must me non 172.16.15.1 is not a internet routable address :-)

A For DNAT, Security rules use pre-NAT IP and post-NAT ZONE.

ANSWER = A

A is correct here. NATpol uses preNAT zones and SECpol uses postNAT zones and preNAT addresses.

hmm not sure A is correct. I think B - security policy is post NAT zone and address where packet comes to rest?