F5CAB3 Exam Dumps and Practice Questions

This question addresses the critical architectural distinction between 'member-based' and 'node-based' load balancing in environments where servers are multi-homed or host multiple virtualized services. On a BIG-IP, a node represents the underlying IP address of a physical or virtual server, while a pool member represents a specific combination of that IP and a service port (e.g., 10.1.1.10:80).

When multiple pools reference the same IP address across different ports or Virtual Servers, using Least Connections (member) (Option D) only balances connections relative to that specific pool. For example, if Pool_A and Pool_B both use Server_X, and Pool_A has 100 connections while Pool_B has only 5, a member-based algorithm for Pool_B only sees the 5 connections and may continue to send traffic there even if Server_X is CPU-saturated by Pool_A.

The Least Connections (node) algorithm (Option B) solves this by tracking the aggregate total of all active connections directed to that specific node (IP address) across every pool on the system. By selecting the node with the absolute lowest total connection count, the BIG-IP ensures a more equitable distribution of work at the hardware resource level. Predictive methods (Options A and C) use a ranking system based on the trend of connection counts over time, but for the specific requirement of maintaining an equal number of current connections on multi-service servers, the direct Least Connections (node) calculation is the standard and most effective procedural choice.

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.

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.

When clients connect through a single source IP (NAT) --- such as a corporate proxy or carrier-grade NAT --- Source Address Affinity persistence becomes entirely ineffective because all clients share an identical source IP address. This would force every client session to the same pool member, completely eliminating even distribution and defeating the purpose of load balancing.

Cookie Persistence is the optimal solution in this scenario because it operates at Layer 7, inserting a unique cookie into each client's HTTP/HTTPS response. Each individual browser session carries its own distinct cookie value, allowing the BIG-IP to identify and persist individual clients to specific pool members --- regardless of whether they share a common source IP address. This guarantees both session persistence and even load distribution across pool members.

The remaining options are unsuitable because:

Destination Address Affinity persists based on destination IP, irrelevant for client-to-server session stickiness.

SSL Persistence uses the SSL Session ID for persistence, but SSL session IDs are frequently renegotiated and are unreliable for long-term persistence across modern TLS implementations.

Source Address Affinity fails entirely under NAT conditions as described.

Cookie persistence is the industry-standard method for HTTPS application load balancing requiring per-client session affinity.

When the connection limit is reached, BIG-IP resets new connections, even if pool members are healthy.