F5 F5CAB3 - BIG-IP Administration Data Plane Configuration (F5CAB3) exam

To fulfill the requirement of "SSL Offload" limited to "TLSv1.2 only," the administrator must focus on the client-side of the connection. SSL Offload means the BIG-IP terminates the encrypted connection from the user, processes the traffic (often as plain text internally), and optionally sends it to the backend. The profile responsible for this termination and the initial negotiation with the client's browser is the Client SSL Profile.

A custom Client SSL Profile must be created because the default clientssl profile typically allows a broad range of protocols for compatibility (including TLS 1.0, 1.1, and 1.2). To restrict communication specifically to TLS 1.2, the administrator modifies the Ciphers string within the profile. Using a string such as DEFAULT:!SSLv3:!TLSv1:!TLSv1.1 or specifically defining TLSv1.2-only suites ensures that the BIG-IP will reject any handshake attempts from older, less secure protocols.

Server SSL Profiles (Options B and C) are used for the encryption between the BIG-IP and the backend nodes, which is not what is requested here. Simply selecting "no TLSv1" in an options list (Option D) is insufficient and often refers to older versions of the software; the modern and standard way to control protocol negotiation on a BIG-IP is through the precise application of Cipher Strings within the Client SSL profile. This ensures compliance with security standards like PCI-DSS while providing the offloading benefits to the backend infrastructure.

Similar to the logic required for managing multi-service backend environments, the issue described—where servers hosting multiple protocols like FTP and HTTP are experiencing uneven distribution—stems from the BIG-IP's default behavior of treating each pool independently. If the administrator uses a member-based load balancing method, the BIG-IP distributes HTTP traffic regardless of how much FTP traffic that same physical server is currently processing.

To resolve this, the administrator must utilize the Least Connections (Node) method. By switching both the HTTP and FTP pools to this algorithm, the BIG-IP begins to make load balancing decisions based on the total combined connection count for the IP address of each server. When a new HTTP request arrives, the BIG-IP checks which server has the fewest total connections (including existing FTP sessions). This prevents a server that is already busy with long-lived FTP transfers from being overwhelmed by a sudden burst of HTTP requests.

Ratio methods (Options A and C) are static and rely on the administrator manually assigning weights to servers based on their perceived capacity; they do not adapt to real-time fluctuations in traffic volume across different pools. Least Connections (Member) (Option B) remains blind to the "cross-pool" traffic on the same hardware. Only the Node-based Least Connections approach provides the global visibility necessary to "even out" the total resource utilization across servers supporting multiple distinct applications.

Connection rate limits restrict how many new connections are accepted per second, protecting application resources.

Fallback persistence is used when the primary persistence method fails. Source Address Affinity is a Layer 4 persistence method and is fully supported as a fallback option for most virtual server types.

WAN-optimized TCP profiles improve performance for high-latency Internet clients, while LAN profiles are optimal for backend servers.

Using “at least one” ensures each member is marked up based on its relevant service monitor.

In F5 BIG-IP administration, iApps are designed to manage complex application configurations as a single unit. When an iApp is deployed, it creates an "Application Service" object that owns all the associated LTM objects, such as Virtual Servers, Pools, and Nodes. By default, these iApps are created with Strict Updates enabled. Strict Updates is a safety mechanism that prevents administrators from making manual "out-of-band" changes to the individual objects created by the iApp. The system enforces this because manual changes would be overwritten the next time the iApp template is updated or re-entered.

When the administrator attempts to change the destination IP address directly on the Virtual Server object, the BIG-IP system checks the "Strict Updates" flag. If it is set to "Enabled," the system blocks the modification and generates the error message stating the service must be updated via the application management interface. To resolve this, the administrator must navigate to the iApp >> Application Services menu, select the specific application service, and go to the "Reconfigure" tab. Within the iApp configuration form, the destination IP can be safely changed. Alternatively, if the administrator specifically wants to manage the objects manually and forgo the benefits of the iApp template management, they could disable "Strict Updates" in the iApp properties, though this is generally discouraged as it breaks the template's logic. The error is not related to subnetting or duplicate IPs, but strictly to the configuration authority assigned to the iApp service.

Standard DNS queries use UDP. Configuring the Virtual Server for TCP causes DNS traffic to fail.

The issue described is a classic symptom of asymmetric routing, which frequently occurs when the BIG-IP system and the back-end servers reside on the same subnet (often referred to as a "one-arm" deployment).

The Routing Problem: By default, the BIG-IP system preserves the original client source IP address when forwarding traffic to a pool member. If the server is in the same subnet as the client or if the server's default gateway is not the BIG-IP, the server will attempt to send its response directly back to the client’s IP address, bypassing the BIG-IP.

Stateful Failure: Since the BIG-IP is a Full Proxy, it maintains a state table. Because the response packet never returns through the BIG-IP, the system cannot complete the three-way handshake or manage the application session, resulting in a connection failure for the user.

The Solution (SNAT): Enabling Source Network Address Translation (SNAT) solves this by changing the source IP address of the request to an IP address owned by the BIG-IP (typically a self-IP).

Requirement for Subnet Alignment: To ensure the server sends the response back to the BIG-IP, the translation address must be reachable. By using a self-IP configured in the same subnet as the servers, the BIG-IP ensures that the server sees the request coming from a local "neighbor." The server will then naturally send the response back to that self-IP, allowing the BIG-IP to translate the packet back and forward it to the client.

Why other options are incorrect:

A: Disabling address translation would ensure the server-side traffic uses the client IP, making asymmetric routing inevitable in this scenario.

B: This is technically contradictory; "Auto Map" specifically uses existing self-IPs and does not require or use a "SNAT pool" configuration.

C: While using a specific translation address can work, it does not inherently guarantee the Layer 2/Layer 3 reachability mentioned in the scenario as effectively as ensuring the self-IP is correctly placed in the server's subnet.

A red diamond indicates that the Virtual Server is enabled but unavailable, typically due to all pool members being down.