F5CAB3 Exam Dumps - F5-CA Questions and Answers

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.

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.

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

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.

Standard DNS queries use UDP. Configuring the Virtual Server for TCP causes DNS traffic to fail.

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

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 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 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.

With manual resume enabled, BIG-IP does not automatically return a pool member to service after recovery. The member remains offline until manually re-enabled.

The X-Forwarded-For header preserves the original client IP when SNAT is enabled.

The log message “Intercept exhaustion” indicates that the BIG-IP system has exhausted the available source port translations for one or more SNAT addresses. This occurs when too many concurrent client connections are being translated through a limited number of SNAT IP addresses, and all ephemeral source ports (typically ~64,000 per SNAT IP) are in use.

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

Each SNAT IP address provides a finite number of available source ports.

When the number of concurrent connections exceeds the available port space, the BIG-IP logs an Intercept exhaustion error and new connections fail.

The recommended resolution is to increase the available SNAT resources by adding additional IP addresses to the SNAT pool.

Why the other options are incorrect:

A. Increase the timeout of the SNAT addressesIncreasing timeouts may actually worsen the problem by keeping ports allocated longer, accelerating port exhaustion.

B. Remove the SNAT pool and apply SNAT AutomapSNAT Automap uses the Self IP addresses on the egress VLAN, which may not provide additional capacity and can introduce routing or design issues. This is not a direct or recommended fix for SNAT exhaustion.

C. Remove an IP address from the SNAT poolThis would reduce the number of available source ports and further exacerbate the intercept exhaustion condition.

Correct Resolution:

By adding an IP address to the SNAT pool, the BIG-IP increases the total number of available source ports, alleviating intercept exhaustion and restoring successful client connections.