F5CAB3 BIG-IP Administration Data Plane Configuration (F5CAB3) exam Questions and Answers

This scenario describes a classic case of asymmetric routing in a "one-arm" or non-gateway deployment. When a BIG-IP system is configured for SSL offloading, the following traffic flow occurs:

Client-Side: The client establishes a successful SSL/TLS handshake with the Virtual Server. This explains why the user can "successfully establish an SSL connection."

Server-Side: The BIG-IP decrypts the traffic and forwards it as plain HTTP to the backend server. The packet trace confirms the server receives the HTTP GET request and responds with the content.

The Routing Failure: By default, the BIG-IP system preserves the client's original source IP address. If the backend server's default gateway is not the BIG-IP system (or if the server is on the same subnet as the client), the server will attempt to send the response directly back to the client's IP address, bypassing the BIG-IP.

Stateful Drop: Because the BIG-IP is a Full Proxy, it expects the response to return through its own internal state table to be encrypted and sent back to the client. Since the response bypasses the BIG-IP, the BIG-IP connection eventually times out, and the client receives no data despite the server having sent it.

Solution (SNAT): Enabling Secure Network Address Translation (SNAT), specifically SNAT Auto Map, ensures that the BIG-IP replaces the client's source IP with its own internal self-IP before sending the request to the server. This forces the server to send the response back to the BIG-IP, allowing the BIG-IP to complete the transaction and deliver the content to the user.

BIG-IP provides several built-in TCP profiles optimized for different traffic patterns and network conditions. When attempting to improve general TCP performance, the recommended starting point is f5-tcp-progressive.

According to the BIG-IP Administration: Data Plane Configuration documentation:

f5-tcp-progressive is designed as a balanced, general-purpose TCP optimization profile.

It dynamically adjusts TCP behavior to improve throughput and latency for most enterprise applications.

It is the recommended first-choice profile when tuning TCP performance before moving to more specialized profiles.

Why the other options are incorrect:

A. f5-tcp-legacyThis profile exists for backward compatibility and does not include modern TCP optimizations.

C. f5-tcp-mobileThis profile is optimized specifically for high-latency, lossy mobile networks and is not suitable for general-purpose environments.

D. No optionBIG-IP explicitly provides built-in TCP profiles for performance tuning; using none would forgo optimization opportunities.

Correct Resolution:

The administrator should first apply f5-tcp-progressive to evaluate potential TCP performance improvements before considering more specialized profiles.

In F5 BIG-IP systems, an iApp is a template-driven framework used to deploy and manage application-specific configurations. When an iApp is deployed, the system creates a specialized folder or "Application Service" container to hold all the resulting Local Traffic Manager (LTM) objects, such as virtual servers, pools, and profiles. This container is visually and programmatically identified by the .app extension in its path name.

The naming convention for these objects follows a specific hierarchical structure: //.app/. For example, if an administrator creates an iApp named "testhttp" in the "/Common" partition, the virtual server created by that iApp would be identified in the configuration (TMSH) and the GUI as /Common/testhttp.app/testhttp. This structure allows the BIG-IP system to distinguish between manually created objects and those managed by the iApp's automation logic.

This identification is crucial because iApp-managed objects typically have Strict Updates enabled, which prevents administrators from making direct manual changes to the object settings outside of the iApp's reconfigure interface. Attempting to modify such an object directly will result in an error message stating that the application service must be updated using an application management interface. By recognizing the .app path and the repeated name within the structure, an administrator can immediately identify that the object belongs to an iApp and should be managed through the iApp's specific management screen rather than standard LTM configuration menus.

When many users share one source IP, source-address persistence fails. Cookie persistence uniquely identifies clients at Layer 7.

From the exhibit, the pool contains different applications on different service ports (for example, HTTP/80, FTP/21, HTTPS/443, SSH/22). To mark pool members correctly, BIG-IP must be able to verify the actual service running on each member’s port.

In BIG-IP Administration: Data Plane Configuration, monitor behavior is described as follows:

When multiple monitors are assigned to a pool, the Availability Requirement controls how monitor results are evaluated:

At least one = the pool member is marked up if any one of the assigned monitors succeeds.

All = the pool member is marked up only if every assigned monitor succeeds.

For pools containing members with different services/ports, using All can incorrectly mark members down because monitors intended for other services will fail on the wrong port.

Why C is correct:

Assigning HTTPS, HTTP, FTP, and SSH covers the actual services shown in the pool.

Setting the Availability Requirement to at least one ensures that each pool member is considered available when its appropriate service monitor succeeds, without being forced to pass unrelated service monitors.

Why the other options are incorrect:

A / D (Availability Requirement = all): would cause members to be marked down when unrelated monitors fail (e.g., SSH monitor against an HTTP member).

B (includes ICMP): ICMP can indicate the host is reachable even if the application service is down, which does not “accurately” reflect service availability.

Therefore, the best choice is HTTPS, HTTP, FTP, and SSH with Availability Requirement of at least one health monitor.

Slow Ramp Time prevents new pool members from receiving full traffic immediately, avoiding overload.

The log message "aggressive mode activated" indicates that the BIG-IP's adaptive connection management system (the "Sweeper") has detected that the system's memory or connection limits are reaching a critical threshold. To protect the system from crashing due to memory exhaustion (OOM), the BIG-IP enters Aggressive Mode, where it begins to proactively and rapidly reap (close) idle connections to free up resources for new incoming traffic.

To mitigate this and return the system to a healthy state, the administrator needs to reduce the overall resource footprint of existing connections. Decreasing the TCP profile Idle Timeout value (Option B) is the most effective administrative action. In many environments, the default idle timeout is 300 seconds (5 minutes). If a large number of connections remain "open" in the BIG-IP connection table long after the clients have stopped sending data, they consume valuable TMM (Traffic Management Microkernel) memory. By lowering the timeout (e.g., to 60 or 120 seconds), the BIG-IP can expire and remove these inactive entries much sooner, preventing the connection table from bloating and triggering the Sweeper's aggressive mode.

Conversely, increasing the timeout (Option C) would exacerbate the problem by keeping "dead" connections in memory even longer. Connection Mirroring (Option D) actually increases memory usage because every connection must be duplicated on the standby peer. An active-active configuration (Option A) might spread the load but does not address the underlying resource management issue on the individual units. Therefore, tightening the idle timers is the standard procedural fix for memory pressure caused by high connection volumes.

For HTTP-based applications, cookie persistence is the most appropriate and commonly recommended persistence method.

According to the BIG-IP Administration: Data Plane Configuration documentation:

Cookie persistence inserts or uses an HTTP cookie to maintain session affinity.

It operates at Layer 7 (HTTP) and is application-aware.

It allows persistence to be maintained even when multiple clients are behind a NAT device.

Why the other options are incorrect:

A. Destination addressDestination address persistence is generally used for inbound traffic patterns such as firewall or proxy scenarios.

B. Hash persistenceHash persistence is less granular and not HTTP-specific.

C. SSL persistenceSSL persistence is typically used when SSL session IDs are reused and is less reliable than cookies for HTTP applications.

Correct Resolution:

Using cookie persistence ensures that HTTP web requests are consistently directed to the same pool member.

The requirement states that load balancing decisions must be based on the number of active connections on each pool member. This directly maps to the Least Connections (member) load balancing method.

According to the BIG-IP Administration: Data Plane Configuration documentation:

Least Connections (member) selects the pool member with the fewest active connections at the time of the request.

This method dynamically adapts to real-time traffic patterns and ensures that more heavily loaded pool members receive fewer new connections.

It is especially effective for web servers where connection duration may vary and equal distribution of active sessions is desired.

Why the other options are incorrect:

B. Round RobinDistributes connections sequentially without considering current load or active connections.

C. Ratio (member)Distributes traffic based on static ratios, not real-time connection counts.

D. Ratio (node)Uses predefined ratios at the node level and does not account for active connection counts.

Correct Resolution:

Using Least Connections (member) ensures that new connections are directed to the pool member currently handling the fewest active connections, meeting the stated requirement.

Standard BIG-IP administration dictates that hardware-level physical attributes are managed within the Network section of the configuration. When a network switch and a BIG-IP fail to successfully negotiate speed and duplex settings (Auto-Negotiation), it can result in CRC errors, late collisions, or a total lack of link. To resolve this manually, the administrator must navigate to the Configuration Utility (GUI) and go to Network > Interfaces.

Within the Interfaces list, the administrator can select the specific physical port (e.g., 1.1 or 1.2) and modify its properties. By default, the media speed is set to "Auto," but the drop-down menu allows for manual selection of specific speeds (e.g., 100Mb/s, 1Gb/s, 10Gb/s) and duplex settings (Full or Half). While these changes can also be made via the TMOS Shell (TMSH) (Option B) using the modify net interface command, the question asks for the standard location, which in most administrative contexts refers to the primary GUI path. System > Configuration (Option D) is used for global device settings like NTP, DNS, and licensing, not for interface-specific physical layer parameters. The Front Console (Option A), referring to the LCD panel on physical appliances, is primarily used for initial management IP setup and viewing system alerts, but does not provide the granular interface configuration required for media speed adjustments.

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

Slow Ramp Time prevents new members from being overwhelmed immediately after activation.

According to the provided exhibit, the "SSL Profile (Client)" section in the Virtual Server configuration is empty. For a BIG-IP system to process HTTPS traffic, it must act as an SSL/TLS endpoint. This process, known as SSL Termination or SSL Offload, requires the assignment of a Client SSL Profile to the Virtual Server. Without this profile, the BIG-IP does not have the necessary certificate and private key information to perform the SSL handshake with the client's browser. Consequently, when a user attempts to connect via HTTPS, the TCP connection may establish, but the SSL handshake will fail because the BIG-IP will not know how to decrypt the incoming encrypted packets.

A Client SSL profile defines the ciphers, certificates, and keys that the BIG-IP uses to communicate securely with the client. In a standard HTTPS deployment, the BIG-IP decrypts the traffic and can then send it to the backend pool members either as plain text (header insertion/manipulation) or re-encrypt it using a Server SSL profile. While a Server SSL profile (Option C) is needed if the backend servers themselves require HTTPS, the initial failure for a user reaching a Virtual Server is almost always the lack of a Client SSL profile to terminate the user's connection. Changing the Service Port to HTTP (Option D) would be incorrect because the goal is to handle HTTPS traffic (typically port 443). Assigning the "clientssl" or a custom client-side profile from the "Available" list to the "Selected" list in the GUI is the mandatory step to make the Virtual Server operational for secure web traffic.

The BIG-IP Configuration Utility (GUI) organizes information hierarchically to allow for granular management of application objects. A Pool is a collection of backend servers (pool members) that provide the same service. To verify the specific network parameters—such as the IP address and the service port—of the servers within a pool, the administrator must navigate to the specific pool's configuration.

The standard procedural path to verify this is Local Traffic > Pools: Pool List, where the administrator selects the specific pool name. Once inside the pool's configuration, the Members tab displays a list of all IP addresses and service ports associated with that pool. Under the "Service Port" column, the administrator can confirm if the member is listening on port 80 (HTTP).

Options A and B are incorrect for this specific verification task. While Nodes (Option A) show the health of a physical server, a node represents only an IP address and does not have a "Service Port" associated with it until it is defined as a pool member. Verifying the Health Monitor (Option B) would tell the administrator how the system is checking the member's status, but it does not definitively show the port on which the member is actually receiving application traffic. In a BIG-IP environment, a pool member is uniquely identified by the combination of its Node IP and its Service Port, and the Members tab is the primary interface for managing and auditing these specific member attributes.

By default, BIG-IP load balancing algorithms (such as Round Robin) distribute connections evenly across all available pool members. However, persistence profiles override normal load balancing decisions by forcing subsequent connections from a client to be sent to the same pool member.

According to the BIG-IP Administration: Data Plane Configuration documentation:

Persistence creates a client-to-server mapping that is honored before load balancing algorithms are applied.

When persistence is enabled, BIG-IP may repeatedly select the same pool member even if others are available.

This directly alters load balancing behavior.

Why the other options are incorrect:

A. Adding a OneConnect profileOneConnect optimizes server-side TCP connections but does not change which pool member is selected.

B. Enabling SNAT automapSNAT affects source address translation, not pool member selection.

C. Enabling a fallback host in the HTTP profileA fallback host is only used when no pool members are available.

Correct Resolution:

Adding a persistence profile alters load balancing behavior by maintaining client affinity to a specific pool member.

SNAT Automap is a common configuration that replaces the client's original source IP address with one of the BIG-IP's self IP addresses. This ensures that the backend servers send return traffic back through the BIG-IP, which is necessary for the ADC to process the traffic correctly. However, a side effect of SNAT is that the backend servers only see the BIG-IP's IP in their logs, losing visibility into the true identity of the client.

To resolve this while still using SNAT for routing purposes, the administrator must configure the BIG-IP to "pass" the client's IP address at the application layer. This is achieved by using an HTTP Profile with the Insert X-Forwarded-For setting enabled. When this profile is applied to the Virtual Server, the BIG-IP intercepts the HTTP request, adds a header (X-Forwarded-For) containing the client's original IP, and then forwards the modified request to the server. The backend web server can then be configured to read this header and log the original client IP instead of the BIG-IP's SNAT address.

Other options are incorrect for this requirement. Performance (HTTP) (Option A) is a virtual server type optimized for speed but often lacks the full Layer 7 header manipulation capabilities of a Standard Virtual Server. SNAT Pool with the client IP (Option C) is technically impossible as SNAT pools use static, pre-defined IPs. There is no such thing as an HTTP Transparent profile (Option D) in standard BIG-IP administration for this purpose. The X-Forwarded-For header insertion within the HTTP profile is the standard procedural method for maintaining client visibility in SNAT-enabled environments.

When multiple users share one source IP, source-address persistence fails. Cookie persistence uniquely identifies users at Layer 7 and ensures correct session handling.

In a BIG-IP environment, a Fallback Persistence Profile is utilized as a secondary "stickiness" mechanism when the primary (Default) persistence method fails to provide a valid persistence record. For example, if a Virtual Server uses HTTP Cookie Persistence as its primary method, but a client’s browser has cookies disabled, the BIG-IP will be unable to find a persistence cookie in the request. Without a fallback method, the system would treat every request from that client as a new, independent connection, potentially breaking the application session.

Source Address Affinity (also known as Source Address Persistence) is the most common and standard choice for a fallback profile. It operates at the network layer (Layer 3) by tracking the client’s source IP address. Because every IP packet contains a source address, this method is virtually guaranteed to work even when application-layer data (like Cookies or SSL Session IDs) is missing or encrypted beyond the BIG-IP's visibility. While Universal (Option A) and Hash (Option D) profiles are highly flexible and can use iRules to persist on almost any data, they require specific configuration and logic that may not always be present or valid. SSL persistence (Option C) relies on the SSL Session ID, which frequently changes due to modern browser security practices (session renegotiation), making it less reliable than Source Address Affinity. By configuring Source Address Affinity as the fallback, the administrator ensures that the BIG-IP has a "safety net" to maintain session integrity based on the client's IP address when the more granular cookie-based persistence is unavailable.

The BIG-IP system uses a centralized management framework to ensure that all devices within a Sync-Failover group share a consistent configuration. When an administrator makes a change on any member of the group—whether it is the active or the standby device—the system detects a "ConfigSync" mismatch. The "Device Management >> Overview" screen tracks these changes by comparing the commit ID and timestamps of the configurations across all peers.

If a change is made on the standby member, that device now possesses a more recent configuration than the other members of the group. Consequently, the BIG-IP GUI will display a status of "Changes Pending" and suggest a Recommended Action to resolve the discrepancy. In this scenario, the correct action is to Synchronize the standby member configuration to the group. This push operation will copy the updated configuration from the standby device to the active device (and any other peers), bringing the entire cluster back into a "In Sync" status. It is important to note that BIG-IP allows bi-directional synchronization; you do not have to be on the active device to push a configuration. However, administrators must be cautious: choosing Option C (Synchronizing the active member to the group) would overwrite the changes just made on the standby device with the older configuration from the active device, effectively reverting the changes. The Recommended Action always points toward the direction that propagates the most recent change to the rest of the group.