Master the Palo Alto Networks Certified Security Engineer (PCNSE) PAN-OS 11.0 PCNSE Exam with Confidence!

The two key exchange algorithms that consume the most resources when decrypting SSL traffic are ECDHE and DHE. These are both Diffie-Hellman based algorithms that enable perfect forward secrecy (PFS), which means that they generate a new and unique session key for each SSL/TLS session, and do not reuse any previous keys. This enhances the security of the encrypted communication, but also increases the computational cost and complexity of the key exchange process. ECDHE stands for Elliptic Curve Diffie-Hellman Ephemeral, which uses elliptic curve cryptography (ECC) to generate the session key. DHE stands for Diffie-Hellman Ephemeral, which uses modular arithmetic to generate the session key. Both ECDHE and DHE require more CPU and memory resources than RSA, which is a non-PFS algorithm that uses public and private keys to encrypt and decrypt the session key123. References: Key Exchange Algorithms, Best Practices for Enabling SSL Decryption, PCNSE Study Guide (page 60)

The engineer should adjust the TCP maximum segment size (MSS) value on ethernet1/1 to remedy this problem. This is because the MTU on an upstream router interface is set to 1400 bytes, which is causing the return traffic from the web servers to not reach the users behind the firewall. By adjusting the TCP MSS value, the engineer can ensure that the return traffic is able to reach the users without any issues.

The TCP MSS is the maximum amount of data that can be transmitted in a single TCP segment, excluding the TCP and IP headers. The TCP MSS is usually derived from the MTU of the underlying network, which is the maximum packet size that can be transmitted without fragmentation. For example, if the MTU is 1500 bytes, which is the default value for ethernet interfaces, then the TCP MSS is 1460 bytes (1500 - 20 bytes for IP header - 20 bytes for TCP header). However, if there are intermediate devices or networks that have a lower MTU than the end-to-end path, then the TCP MSS may need to be adjusted accordingly to avoid packet loss or fragmentation1.

In this case, the firewall has an MTU of 1500 bytes on ethernet1/1, which is connected to a WAN link. However, an upstream router has an MTU of 1400 bytes on its interface, which means that any packet larger than 1400 bytes will be either dropped or fragmented by the router. This can cause problems for the return traffic from the web servers, which may have a TCP MSS of 1460 bytes or higher, depending on their MTU settings. If these packets have the Don’t Fragment (DF) bit set in their IP header, which is common for TCP packets, then they will be dropped by the router and never reach the firewall or the users behind it. If they do not have the DF bit set, then they will be fragmented by the router and reassembled by the firewall, which can cause performance degradation and overhead2.

To avoid these problems, the engineer should adjust the TCP MSS value on ethernet1/1 to match or be lower than the MTU of the upstream router. This can be done by using the CLI command set network interface ethernet ethernet1/1 tcp-mss , where is an integer between 64 and 15003. For example, if the engineer sets the TCP MSS value to 1360 bytes (1400 - 20 - 20), then this will ensure that any TCP packet sent or received by ethernet1/1 will not exceed 1400 bytes in total size, and thus will not be dropped or fragmented by the router. This will allow the return traffic from the web servers to reach the users behind the firewall without any issues4.

References: TCP Maximum Segment Size (MSS), Configure Session Settings, TCP MSS Adjustments, PCNSE Study Guide (page 59)

Palo Alto Networks' WildFire service is designed to perform advanced analysis on files to identify and protect against new and evolving threats. When a WildFire analysis profile is configured to forward any file type to the WildFire public cloud, the service analyzes files that pass through the firewall based on the policy configuration.

D. Does not perform malicious content analysis on the linked page, but performs it on the corresponding PE file:

• When a user clicks on an unknown link that downloads a Portable Executable (PE) file, WildFire's primary focus is on the file itself rather than the webpage from which it originated. The service analyzes the PE file to determine if it contains malicious content. This analysis includes static and dynamic inspection techniques to uncover any malicious behavior.
• The webpage hosting the link may not be analyzed as part of this process unless specific protections or URL filtering policies are in place that trigger such an analysis. The primary concern in this scenario is the PE file, which is directly analyzed by WildFire for malicious content.

By focusing on the files that could pose a direct threat to the network, WildFire provides a robust mechanism for identifying and mitigating potential security risks associated with file downloads.