F5 BIG-IP Administration Support and Troubleshooting (F5CAB5) exam F5CAB5 Exam Dumps: Updated Questions & Answers (December 2025)

When load balancing is not working as expected across hardware hosting multiple services, the administrator must distinguish between "member" and "node" level algorithms102102102102. A "member" is a specific IP and port (e.g., 10.1.1.1:80), while a "node" is the physical server's IP (10.1.1.1) regardless of the port103. If servers host both FTP and HTTP services in separate pools, using "Least Connections (Member)" only balances connections within each individual pool. This can lead to a skewed distribution where one server is selected for a new HTTP connection because it has the fewest HTTP connections, even if it is currently overloaded with hundreds of FTP connections. By applying "Least Connections (Node)," the BIG-IP tracks the total number of connections to the physical hardware across all ports and pools106106106106. This ensures that the administrator can maintain an even distribution of the total workload across the server fleet, resolving the reports of uneven traffic distribution reported by the server support team

When a BIG-IP system experiences high overall CPU usage, troubleshooting requires identifying which specific application or service is the primary consumer of resources. While the system-wide performance graphs provide a global view, the granular data necessary to isolate a "top talker" is found in the "Local Traffic" statistics. Navigating to Statistics > Module Statistics > Local Traffic > Virtual Servers allows the administrator to see specific metrics for each configured virtual server, including the number of packets processed, current connections, and critical CPU cycles consumed. This is essential for troubleshooting performance issues where an inefficient iRule, high SSL handshake volume, or complex L7 profiles (like Compression or ASM) might be overtaxing the Traffic Management Microkernel (TMM) for one specific application. By reviewing these basic stats, an administrator can determine if a performance bottle-neck is a system-wide h1ardware issue or if it is isolated to a single virtual server, enabling targeted remediation such as optimizing iRule logic or moving the high-load virtual server to a dedicated device.

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.

Troubleshooting failed SSL handshakes involves interpreting the resource limits defined by the system's license8888. The log message SSL transaction (TPS) rate limit reached indicates the BIG-IP is dropping SSL connections because it has exceeded its licensed "Transactions Per Second" capacity. When analyzing stats to determine the correct license level, the administrator must focus on "Client-side" SSL TPS. This represents the initial encrypted handshakes between users and the BIG-IP virtual servers91. In this scenario, the peak client-side demand is 1200 TPS. While the 800 server-side transactions represent re-encryption toward the backend, F5's primary SSL TPS license limits typically apply to the client-facing side of the traffic flow. Therefore, to resolve the intermittent connectivity issues and ensure the virtual server works reliably during peaks, the license must be upgraded to at least 1200 TPS949596969696.9798Confirming this peak via statistics andcomparing it to the current license is a standard troubleshooting step for SSL performance issues.

The exhibit shows the virtual serverapplication_vswith a status indicating it isoffline but enabled. In BIG-IP terminology, this status means the virtual server itself is administratively enabled, but it is unable to pass traffic becauseno usable pool members are available.

Two common and documented causes for this condition are:

Pool member(s) administratively disabled (Option A):When all pool members are administratively disabled, BIG-IP removes them from load-balancing decisions. Even though the virtual server remains enabled, it has no available pool members to send traffic to, resulting in an offline status.

Node(s) administratively disabled (Option C):Pool members inherit the status of their parent nodes. If a node is administratively disabled, all associated pool members are also marked unavailable. This condition causes the virtual server to show as offline, even though the virtual server configuration itself is correct.

The other options are incorrect:

Forced offline pool members (Option B)result in a different operational intent and are explicitly set for maintenance scenarios.

Virtual server administratively disabled (Option D)would show the virtual server as disabled, not enabled/offline.

This behavior is consistent with BIG-IP traffic management logic and is commonly verified by reviewingpool and node availability stateswhen diagnosing virtual server availability issues.

In BIG-IP TMOS administration, the "Forwarding (IP)" virtual server type is unique because it is designed to act as a high-performance router rather than a typical load balancer. Unlike a "Standard" virtual server, which terminates a connection and directs it to a specific pool of members, a Forwarding (IP) virtual server is intended to forward packets based on the system’s routing table. Consequently, the configuration for this type of virtual server explicitly removes the option to associate a default pool. If an administrator is troubleshooting a scenario where they cannot assign a pool to a virtual server, they must verify if the type was accidentally set to Forwarding (IP). This type is most commonly used for outbound internet traffic (outbound SNAT) or to allow the BIG-IP to serve as a gateway between internal subnets. Identifying this constraint is vital for troubleshooting configuration errors where an administrator expects the system to load balance traffic but finds the pool association settings are grayed out or unavailable in the Configuration Utility.

When a virtual server's traffic flow is disrupted only during failover events and takes several minutes to stabilize, the issue is typically related to the ARP cache on upstream network devices47. By default, each BIG-IP in an HA pair uses its own unique hardware MAC address for traffic4848. When a failover occurs, the new active device takes over the floating IP addresses, but the upstream switch may still have the MAC address of the old device cached4949. Traffic fails until the switch's ARP entry is updated. "MAC Masquerade" is a troubleshooting feature that assigns a shared, virtual MAC address to the floating traffic group. Regardless of which BIG-IP is currently active, it will use this masqueraded MAC address for all traffic related to that group52. Because the MAC address seen by the network never changes during a failover, the upstream devices do not need to relearn ARP entries, resulting in an instantaneous transition and eliminating the performance drop reported by users

When traffic "stabilizes after a few minutes" following a failover, it points to a network-level performance issue involving ARP cache on upstream routers and switches. Each BIG-IP interface has a unique hardware MAC address. During failover, the Standby device takes over the floating IP address, but the upstream switch still associates that IP with the MAC of the now-offline device. Traffic is lost until the switch learns the new MAC or its ARP entry expires. "MAC Masquerading" solves this by creating a shared, virtual MAC address for the floating traffic group. This virtual MAC is used by whichever device is currently active. Because the MAC address for the virtual server IP never changes from the perspective of the network, the upstream devices do not need to update their ARP tables. This troubleshooting solution eliminates the delay associated with failover, providing a seamless transition and ensuring that application traffic flow is not disrupted when the BIG-IP HA state changes.

In the BIG-IP Configuration Utility, the status icon (shape and color) provides immediate feedback on why a virtual server is not working as expected81. A "Red Diamond" indicates that the object is "Offline" and unavailable to process traffic82. For a virtual server, this specific status typically means it has inherited an offline state from its mandatory backend resources8383. If all pool members associated with the virtual server have failed their health monitors, the virtual server will transition to a red diamond status because it has no healthy destination for incoming requests. This is distinct from a "Black Circle," which would indicate the virtual server has been manually "Disabled" by an administrator85858585. To troubleshoot a red diamond, the administrator must examine the associated pool and its members to determine why the health monitors are failing (e.g., server crashes, network path failures, or incorrect monitor strings). Resolving the health check failures on the pool members will return the virtual server to an "Available" (Green) status.

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.