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

SSH is a Layer 4 TCP-based protocol that operates on TCP port 22 and does not use HTTP in any capacity. In the exhibit, the Virtual Server is configured with an HTTP Profile applied, which is inappropriate for SSH traffic and causes connection failures.

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

An HTTP profile must only be applied to Virtual Servers handling HTTP or HTTPS traffic.

When an HTTP profile is attached, BIG-IP expects HTTP headers and attempts to parse application-layer data.

Non-HTTP protocols such as SSH, FTP (control), SMTP, and other raw TCP services will fail if an HTTP profile is enabled.

Why the other options are incorrect:

A. Set Protocol to UDPSSH uses TCP, not UDP. Changing the protocol would break SSH entirely.

B. Set Source Address to 10.1.1.2The source address setting controls client access restrictions and is unrelated to protocol parsing issues.

C. Set Destination Address/Mask to 0.0.0.0/0The destination address is already valid for a specific SSH service and does not impact protocol handling.

Correct Resolution:

The BIG-IP Administrator should remove the HTTP Profile (set it to None) so the Virtual Server functions as a pure Layer 4 TCP service, allowing SSH connections to pass through successfully.

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.

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.

In this scenario, each backend node (server) hosts multiple services and is referenced by multiple pools and virtual servers. The goal is to ensure an equal number of total connections per backend server, regardless of how many pool members (services/ports) exist on that server.

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

Least Connections (node) tracks the total number of active connections to a node across all pool members and services.

This algorithm ensures load distribution is balanced at the server level, not just at the individual service (member) level.

It is specifically recommended when:

Multiple pool members exist on the same backend server

Multiple virtual servers reference the same backend servers

Why the other options are incorrect:

B. Predictive (member)Predictive algorithms are advanced and traffic-pattern based, but they operate at the member level and do not guarantee equal connections per server.

C. Least Connections (member)This balances connections per pool member, which can overload a server hosting multiple members while still appearing “balanced” per member.

D. Predictive (node)Although node-aware, predictive algorithms are less deterministic and not the best choice when strict equality of connections is required.

Correct Resolution:

Using Least Connections (node) ensures that each backend server carries an equal connection load across all services and pools.

The Local Traffic > Network Map provides a single consolidated view within the BIG-IP Configuration Utility that displays the full relationship hierarchy of all application delivery objects simultaneously. This includes Virtual Servers, their associated Pools, individual Pool Members, applied iRules, profiles, and the health status of each object — all rendered in a single topological screen.

This view is specifically designed for administrators and users who need rapid situational awareness across the data plane without navigating multiple menu screens. Each object is colour-coded to reflect its current availability state (green = available, red = unavailable, yellow = degraded).

The alternative options do not satisfy all requirements:

Local Traffic > Monitors only displays health monitor configurations, not virtual server or pool member relationships.

Statistics provides performance counters and throughput data, not object relationship mapping.

Local Traffic > Virtual Servers lists virtual server configurations individually but does not provide a unified topology view inclusive of pool members and iRules in a single screen.

The Network Map is the authoritative single-pane-of-glass tool for application object visibility on BIG-IP.

Forwarding (IP) virtual servers forward traffic based on routing decisions and do not use pools or pool members.

URI-based traffic steering requires inspection of the HTTP request. BIG-IP processes HTTP headers and URIs in the HTTP_REQUEST event. Pool member selection based on URI must occur before the request is sent to the server, making HTTP_REQUEST the correct event.

In the F5 BIG-IP ecosystem, a standard ICMP health monitor functions by sending an ICMP echo request to a target node and expecting an ICMP echo reply within a specified timeout period. When a node is marked " DOWN " despite the backend server being configured to respond to ICMP, the issue typically lies in the network path or the specific packet exchange between the BIG-IP ' s self IP and the node ' s IP. Running a tcpdump is the most effective next step because it provides a real-time packet capture of the actual monitor traffic leaving the BIG-IP and any return traffic coming back from the server. This allows the administrator to verify if the BIG-IP is actually sending the echo request, if the request is reaching the server, and if the server is indeed replying or if the reply is being dropped by an intermediate firewall or a security policy.

While other tools have their place, they are inappropriate for this specific layer 3/4 connectivity issue. A qkview is a comprehensive diagnostic file used primarily for F5 Support to analyze the entire system ' s state but is overkill for initial connectivity troubleshooting. An ssldump is used for inspecting SSL/TLS handshakes and encrypted payloads, which is irrelevant for a non-encrypted ICMP monitor. A curl command is a tool for testing HTTP/HTTPS application-level responses; it cannot be used to troubleshoot ICMP (ping) connectivity directly. By using tcpdump -ni < vlan_name > host < node_ip > , the administrator can see the ICMP " type 8 " (request) and " type 0 " (reply) packets, immediately identifying if the monitor failure is due to a " Destination Unreachable " message or a simple lack of response, thereby pinpointing the root cause in the data plane.

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.

This question tests precise knowledge of both TMSH command syntax and BIG-IP object namespace hierarchy . Two critical distinctions must be correctly identified:

1. create vs. modify: Since the Trunk already exists and the administrator is adding interfaces to it, the correct verb is modify — not create . Using create on an existing object would either throw an error or attempt to overwrite the object entirely, neither of which is the desired outcome.

2. /sys vs. /net namespace: Trunk objects in BIG-IP reside within the /net namespace, which encompasses network-layer constructs including Trunks, VLANs, Self IPs, and Routes. The /sys namespace is reserved for system-level objects such as management settings, software, and licensing — it does not contain Trunk objects.

Therefore, the only syntactically and functionally correct command is:

tmsh modify /net trunk trunk_A interfaces add {1.3 1.4}

This command appends interfaces 1.3 and 1.4 to the existing trunk_A object without disrupting currently assigned interfaces, increasing aggregated bandwidth accordingly.

Options A and C use the incorrect /sys namespace, and options A and B incorrectly use the create verb for an existing object.

Source Address Affinity (Persistence) works by tracking the source IP address of incoming packets to ensure a client stays connected to the same backend server. The " netmask " setting within the persistence profile determines the " granularity " of this tracking. A netmask tells the BIG-IP how many bits of the source IP address to ignore when creating the persistence record. For example, the current setting of 255.0.0.0 (a /8 mask) means the BIG-IP only looks at the first octet of the IP; this results in all users from the same large Class A network (e.g., everyone from 10.0.0.0 to 10.255.255.255) being persisted to the exact same server, which can lead to severe load imbalance.

To ensure that each unique IP address creates its own individual persistence record, the administrator must set the netmask to 255.255.255.255 (for IPv4). This is a " host mask " or /32, which instructs the BIG-IP to evaluate all 32 bits of the client ' s source IP address. With this setting, 10.1.1.1 and 10.1.1.2 will be treated as distinct entities and can be load balanced to different servers, each maintaining their own " stickiness " . While Option A (255.255.255.0) would group users by their local subnet, only the full 255.255.255.255 mask satisfies the requirement for true unique-IP persistence. This configuration is standard for internet-facing applications where users arrive from diverse locations and the administrator wants to maintain the most granular and balanced distribution of traffic possible.

HTTP Compression on a BIG-IP system is an optimization feature that reduces the size of HTTP responses sent to clients, thereby saving bandwidth and improving page load times for end-users. To implement this functionality on a Virtual Server, the system requires two specific profiles to work in tandem: an HTTP profile and a Compression profile.

The HTTP profile (Option E) is a prerequisite because compression is an application-layer (Layer 7) operation. The BIG-IP must be " HTTP-aware " to parse the incoming requests and outgoing responses. The HTTP profile allows the BIG-IP to inspect the Accept-Encoding header from the client (to see if the client supports gzip or deflate) and to modify the Content-Encoding and Vary headers in the server ' s response. Without the HTTP profile, the Virtual Server operates at Layer 4 (TCP) and sees the traffic only as an opaque stream of bytes, making compression impossible.

The Compression profile (Option B) contains the actual settings and engine for the task. It defines which content types should be compressed (e.g., text/html, application/javascript), the compression level, and the minimum content length required before compression is applied. While a Stream profile (Option D) is used for data replacement (search and replace) and SSL profiles (Option C) are used for encryption, they do not provide compression logic. By applying both the HTTP and Compression profiles, the BIG-IP can successfully intercept server responses, compress the payload according to the configured policy, and deliver the optimized data to the user, effectively offloading the CPU-intensive compression work from the backend web servers.

SSH (Secure Shell) operates over TCP port 22 , making the TCP health monitor the appropriate and correct choice for monitoring pool members in an SSH pool. The TCP monitor establishes a basic Layer 4 connection to each pool member on the designated port, verifying that the server is reachable and actively accepting TCP connections. A successful three-way handshake confirms the pool member is available; a failure marks it down and removes it from load balancing rotation.

The remaining monitor types are inappropriate for this use case:

UDP monitor operates at Layer 4 but uses the connectionless UDP protocol, which is incompatible with SSH since SSH exclusively uses TCP as its transport.

HTTP monitor sends a Layer 7 GET request expecting an HTTP response — irrelevant for an SSH service that does not speak the HTTP protocol.

HTTPS monitor functions identically to HTTP but over TLS — again, completely misaligned with SSH traffic and port behaviour.

For application-specific SSH validation beyond basic TCP connectivity, an external monitor or custom monitor could be used; however, TCP remains the standard and correct built-in monitor for SSH pool verification within the BIG-IP platform.

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

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

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.

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.

The virtual server is intended to process SSH traffic on TCP port 22 , but the exhibit shows that the standard http HTTP profile is assigned. This is the configuration error. An HTTP profile enables BIG-IP Layer 7 HTTP processing and is appropriate only when the virtual server is expected to process HTTP protocol traffic. F5 documentation defines its purpose directly: “An HTTP profile defines the way that you want the BIG-IP system to manage HTTP traffic.”

SSH is not HTTP. It is an independent application protocol transported over TCP , conventionally using port 22 . Therefore, an ordinary SSH load-balancing virtual server should retain the TCP protocol/profile while having HTTP Profile set to None . F5 ' s SSH virtual-server configuration guidance specifically uses service port 22 for SSH and does not require an HTTP profile.

Options B, C, and D do not address the fault. The destination address 10.1.1.2 correctly identifies the virtual server, while source 0.0.0.0/0 appropriately permits clients from any source. Changing the protocol to UDP would be incorrect because SSH requires TCP.

Reference Topics: Virtual Server configuration; HTTP profiles; TCP profiles; application-protocol profile assignment; SSH traffic handling.

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.

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

A 400 Bad Request response from an HTTP/1.1 web server is a definitive indicator that the HTTP request sent by the health monitor is missing a required Host header . In HTTP/1.1, the Host header is mandatory per RFC 7230. Web servers — particularly those hosting named virtual hosts such as www.f5.com — will reject any HTTP/1.1 request that omits the Host header, returning a 400 error, which the BIG-IP monitor interprets as a failed health check, marking all members DOWN.

The correct Send string must include:

The GET request line with HTTP/1.1 protocol declaration

A \r\n (carriage return + line feed) after the request line

The Host: www.f5.com header to satisfy HTTP/1.1 requirements

A \r\n after the Host header

Connection: Close header to instruct the server to close the connection after responding

A final \r\n\r\n to properly terminate the HTTP request headers

Only option C satisfies all these requirements with the correct syntax and Host header inclusion.

Option D (the current configured string) omits the Host header entirely — the root cause of the 400 error. Options A and B are structurally incomplete or syntactically malformed.

In BIG-IP systems, iRules influence traffic only when they are attached to a Virtual Server. If application traffic is being sent to nodes or pool members that are not defined in the pool, this typically indicates that an iRule is overriding the default load-balancing behavior by explicitly selecting a pool or node.

According to BIG-IP Administration: Data Plane Configuration and official F5 guidance:

iRules are associated with Virtual Servers, not directly with pools or nodes.

To determine whether an iRule is actively affecting traffic, the administrator must inspect the Virtual Server configuration.

Explanation of the correct answers:

B. Via the GUI at the Resources tab for the virtual serverThe Resources tab in the Configuration Utility displays all traffic-handling objects applied to the Virtual Server, including assigned iRules. This is the primary GUI location to verify whether an iRule is influencing data plane traffic.

C. Via TMSH with the list /ltm virtual < virtual_server > commandThis TMSH command displays the full Virtual Server configuration, including any iRules listed under the rules section. It is the authoritative CLI method to confirm iRule usage.

Why the other options are incorrect:

A. Via TMSH with the list /ltm rule < irule > commandThis command only shows the contents of an iRule and does not indicate whether the iRule is attached to or used by any Virtual Server.

D. Via the GUI at the iRule tab for the virtual serverBIG-IP does not provide a dedicated “iRule” tab on Virtual Servers. iRules are viewed and managed under the Resources tab.

Correct Conclusion:

To verify whether an iRule is responsible for unexpected node selection, the BIG-IP Administrator must examine the Virtual Server configuration, either through the Resources tab in the GUI or by using TMSH to list the Virtual Server configuration.