F5CAB5 Sample Questions Answers

When a physical network link (like Interface 1.1) reaches its maximum capacity, it creates a bottleneck that negatively impacts network-level performance. To overcome the physical limits of a single interface, BIG-IP administrators use "Trunking," which is the F5 term for Link Aggregation (often implemented via LACP). A trunk object bundles multiple physical interfaces into a single logical link. By creating a trunk with two or more interfaces, the BIG-IP can spread the traffic load across all members of the trunk, effectively doubling or tripling the available bandwidth for the associated VLANs. Beyond performance, troubleshooting redundancy often leads to the use of trunks; if one cable in a trunk fails, the others continue to carry traffic, preventing a complete outage. This is a superior solution to simply increasing MTU (which requires end-to-end support) or manually setting media speeds. In a high-availability environment, configuring trunks is a foundational troubleshooting and optimization step to ensure that traffic spikes do not result in packet loss due to link saturation.

A gateway_icmp monitor checks basic network reachability by sending ICMP echo requests (pings) to the pool member or its gateway. If the pool is markedDOWNwhile the server is confirmed to be online, the most likely cause is thatICMP traffic is being blocked.

Ahost-based firewall active on the server (Option C)can block ICMP echo requests or replies, preventing BIG-IP from receiving a successful response to the health check. This results in the monitor failing and the pool member being marked down, even though the server and application are otherwise functioning normally. This explanation is consistent with the scenario where other servers in the same subnet work correctly, indicating that routing and BIG-IP configuration are not the issue.

The other options are unrelated to ICMP monitoring. Logged-in users (Option A), missing patches (Option B), and stopped HTTP services (Option D) do not affect a gateway_icmp monitor. BIG-IP troubleshooting best practices recommend verifying ICMP reachability and firewall policies when diagnosing ICMP-based monitor failures.

AQKViewis the primary diagnostic file used by F5 Support to analyze BIG-IP system health, configuration, performance, and logs. It collects a wide range of data, including running configuration, license details, module provisioning, hardware status, logs, statistics, and diagnostic command output. Generating a QKView is a standard first step when troubleshooting issues or opening a support case with F5.

In the BIG-IP Configuration Utility (GUI), the correct location to generate a QKView isSystem > Support (Option C). This menu is specifically designed for support and troubleshooting activities. From this section, administrators can create QKView files, upload them directly to F5 iHealth, or download them locally for later analysis or submission to F5 Support.

The other options are incorrect:

System > Configuration (Option A)is used for system-wide settings such as device name, NTP, and DNS.

System > Archive (Option B)is used to create UCS backups, not diagnostic QKViews.

System > Logs (Option D)is used to view and manage log files, not to generate support bundles.

This workflow is clearly documented in BIG-IP Administration and Support guides and is considered a best practice for efficient troubleshooting and support engagement.

Before upgrading a BIG-IP system to a newer TMOS version, it is critical to review known issues to avoid introducing instability or regressions.F5 Bug Tracker (Option B)is a primary resource for this purpose. It allows administrators to search for documented software defects by TMOS version, module, symptom, or bug ID. Using Bug Tracker, an administrator can identify unresolvedissues, fixed bugs, and behavioral changes that may affect their specific deployment, such as traffic handling, high availability, or module-specific functionality. This directly supports proactive troubleshooting and informed upgrade planning.

F5 iHealth (Option D)is another essential tool used during upgrade preparation. iHealth analyzes uploaded UCS or QKView files and correlates the device configuration and software version with F5’s known issues database. It provides actionable reports highlighting critical defects, upgrade risks, interoperability concerns, and recommended target versions. iHealth is especially valuable because it contextualizes known issues based on the actual configuration running on the device.

The other options are not appropriate for verifying known software issues.F5 End User Diagnostics (Option A)is a client-side troubleshooting tool,F5 University (Option C)is a training platform, andF5 Downloads (Option E)is primarily used to obtain software images and release notes, not to analyze known defects in depth.

Comprehensive and Detailed Explanation From BIG-IP Administration Support and Troubleshooting documents: Monitoring resource utilization is essential for maintaining system stability. If the root (/) file system reaches 100% capacity, the BIG-IP may become unresponsive, fail to save configuration changes, or experience daemon crashes83. When the / partition is full, the immediate troubleshooting step is to identify large or unnecessary files—such as old log files, core dumps, or temporary installer files—located specifically within that file system84. In the provided exhibit, /dev/md4 is explicitly listed at 100% usage for the / mount point85. Checking other partitions like /usr (which is at 82% in the exhibit) would not resolve the immediate "Full" status of the root directory86. Administrators often use the du (disk usage) command via the CLI to find the problematic files. Managing disk space is a proactive task; however, when utilization hits 100%, it becomes a reactive troubleshooting emergency that must be resolved to restore the management plane's functionality.

Comprehensive and Detailed Explanation From BIG-IP Administration Support and Troubleshooting documents: When load balancing is not working as 23expected and connections appear skewed across physical hardware, the administrator must distinguish between "member"24 and "node" level balancing. A "member" refers to a specific IP and Port combination (e.g., 10.1.1.1:80), whereas a "node" refers to the underlying IP address (10.1.1.1) regardless of the port25. If a single server hosts multiple services (Web, FTP, API) across different pools, using "Least Connections (member)" would only balance connections within each individual pool26. This could lead to a scenario where one server is overwhelmed because it is winning the "least connections" count in three different pools simultaneously. By selecting "Least Connections (node)," the BIG-IP tracks the total number of concurrent connections to the physical IP address across all pools it belongs to27. This ensures that the administrator can maintain an equal distribution of work across the hardware, preventing performance degradation on backend servers that host multiple application services.

To successfully performSSL offload and re-encryptionon a BIG-IP system, the virtual server must be configured withboth a Client SSL profile and a Server SSL profile. The Client SSL profile enables BIG-IP to decrypt inbound HTTPS traffic from clients, while the Server SSL profile is required tore-encrypt traffic before forwarding it to the pool members.

From the exhibit, the virtual server has aClient SSL profile configured, which allows BIG-IP to accept HTTPS connections from clients. However, there isno Server SSL profile attached, meaning BIG-IP attempts to sendunencrypted HTTP trafficto pool members listening on HTTPS (port 443). This protocol mismatch causes the server-side SSL handshake to fail, resulting in users being unable to connect to the application.

This behavior is well documented in BIG-IP SSL troubleshooting guides: when backend servers expect HTTPS, a Server SSL profile is mandatory to establish a secure connection from BIG-IP to the pool members.

The other options are incorrect:

Removing the Client SSL profile (Option A) would break client-side HTTPS.

The server-side TCP profile (Option B) is unrelated to SSL encryption.

Forward Proxy (Option C) is only used for outbound SSL inspection scenarios.

Therefore, configuring anSSL Profile (Server)is the correct and required solution.

When a pool member is markedDOWN, it indicates that the configured health monitor is failing. The most effective troubleshooting approach is to focus on the monitor behavior and the actual traffic between BIG-IP and the pool member.

Enabling monitor logging (Option B)is a recommended first step. Monitor logging provides detailed information about why the health check is failing, such as timeouts, connection refusals, incorrect responses, or unexpected status codes. This directly correlates with BIG-IP troubleshooting best practices and allows administrators to confirm whether the failure is due to application behavior, incorrect monitor configuration, or network reachability.

Collecting a TCPdump packet capture (Option D)is also a highly effective method. A packet capture allows the administrator to verify whether the monitor probes are being sent, whether responses are received, and whether packets are being dropped, reset, or malformed. This is especially valuable when diagnosing firewall issues, SSL problems, or application-level failures.

Reviewing pool statistics (Option C) is useful for general monitoring but does not explainwhya health monitor is failing. Reviewing the routing table (Option A) is typically unnecessary unless there is evidence of a broader routing issue affecting multiple destinations.

According toofficial F5 documentation (K52015891 – Troubleshooting BIG-IP power supply issues),hardware-related alerts for power supplies, fans, and chassis components are logged in /var/log/ltm.

When a BIG-IP device experiences a power supply issue—such as failure, intermittent outages, or fan-related faults—the system generates alerts through internal platform monitoring services. These alerts are written to the/var/log/ltmfile and often appear with messages similar to:

Chassis power supply 2 has experienced an issue. Status is as follows: FAN=bad; STATUS=bad.

This makes /var/log/ltm theauthoritative log filefor identifying and verifying power supply and chassis-related problems on BIG-IP systems.

The other log files are not appropriate for this purpose:

/var/log/daemon.logcontains general daemon messages but isnot the primary sourcefor chassis hardware alerts.

/var/log/kern.loglogs kernel-level events, not platform power status.

/var/log/auditrecords administrative actions and configuration changes.

Conclusion:

Per F5-supported guidance, when suspecting power supply outages or chassis hardware issues, the BIG-IP Administrator shouldalways check /var/log/ltm first.