F5CAB3 Sample Questions Answers

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 host , 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.

The configuration provided utilizes Priority Group Activation in conjunction with the min_active_members setting. Priority groups allow an administrator to define primary servers and "backup" servers within the same pool. The BIG-IP prioritizes traffic based on the assigned priority number, with the highest number receiving traffic first.

In this specific configuration, the priority 3 group is the primary group. Therefore, connections are first distributed to all pool members with priority 3 as long as they are available. The system will continue to use only the priority 3 group unless the number of available members in that group falls below the min_active_members value, which is set to 2.

If the priority 3 group has fewer than two active members, the BIG-IP "activates" the next available priority group (priority 2) and distributes traffic among the remaining members of priority 3 and all members of priority 2. This cascading logic continues down the list. Consequently, if both the priority 3 group and the priority 2 group have fewer than two members available, traffic is directed to the priority 1 group. This ensures that even in a multi-server failure scenario, the system has a last-resort group of servers to handle the traffic.

Option D is incorrect because if only one member of priority 3 goes down, there are still two members active (10.12.10.8 and 10.12.10.9). Since 2 is not less than the min_active_members threshold of 2, the priority 2 group will not yet be activated. Option B is incorrect because traffic flows from high priority to low priority, not the other way around.

Performance (Layer 4) virtual servers rely on FastL4 profiles to provide high-speed L4 processing without full proxy overhead.

Below is BATCH 2 (next 10 questions) extracted only from your uploaded document that are clearly related to BIG-IP Administration: Data Plane Configuration topics.

❗As requested, I have strictly excluded questions related to:

Licensing

HA / Device Trust / Sync-only

Logging destinations

User roles

Hardware, EUD, support processes

System-only administration

Source: Your uploaded TMOS Administration v2.0 document

SSH is a TCP Layer 4 protocol. Applying an HTTP profile causes BIG-IP to expect HTTP headers, breaking SSH sessions. Removing the HTTP profile allows raw TCP forwarding.

WAN-optimized TCP profiles improve performance for high-latency Internet clients, while LAN profiles are optimal for backend servers.

Connection rate limiting controls how many new connections per second are accepted, protecting backend resources.

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

When multiple hostnames resolve to the same IP address and encrypted communication is required, the BIG-IP must be able to present the correct SSL certificate based on the hostname requested by the client. This is accomplished using Server Name Indication (SNI).

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

SNI is a client-side TLS extension, where the client includes the requested hostname during the SSL handshake.

BIG-IP evaluates this hostname using the Client SSL profile, not the Server SSL profile.

The “Server Name” setting in the Client SSL profile enables BIG-IP to select the appropriate SSL certificate for the requested hostname.

Why option C is correct:

Client SSL profile handles inbound (client-side) encryption.

Server Name enables SNI-based certificate selection when multiple DNS names share the same virtual server IP.

Why the other options are incorrect:

A. Client SSL, Client NameThere is no Client SSL setting called Client Name for SNI certificate selection.

B. Server SSL, Server NameServer SSL is used for encryption between BIG-IP and backend servers, not for client-side hostname identification.

D. Server SSL, Client NameServer SSL does not process client-requested hostnames during TLS negotiation.

Correct Resolution:

Configure a Client SSL profile and enable the Server Name (SNI) setting to support multiple encrypted hostnames on the same virtual server IP.

When a single IP address (Virtual Server) must host multiple hostnames (e.g., site1.com, site2.com) over HTTPS, the BIG-IP must be able to present the correct SSL certificate for each site during the initial handshake. This requirement is handled by a technology called Server Name Indication (SNI).

To implement this on the BIG-IP, the administrator must use a Client SSL profile because the encryption is occurring between the user (Client) and the Virtual Server. Within the Client SSL profile settings, there is a field called Server Name. By creating multiple Client SSL profiles—each with a different "Server Name" (the hostname) and its corresponding certificate—and attaching them all to the same Virtual Server, the BIG-IP can inspect the SNI extension in the client's "Client Hello" packet. It then selects the specific profile that matches the requested hostname.

Option A is incorrect because "Client Name" is not the standard field name used for SNI hostname matching in the profile. Options B and C refer to Server SSL profiles, which manage the connection between the BIG-IP and the backend servers. While Server SSL profiles also have a "Server Name" field (used to send SNI to a backend server), the requirement here is to provide encrypted communication for "users" accessing the virtual server, which definitively requires a Client-side SSL configuration.

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.

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

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.

To provide encrypted communication between users and a virtual server, the BIG-IP system acts as a transparent SSL/TLS proxy. The administrative configuration required for this is a Client SSL profile.

When multiple hostnames (FQDNs) are associated with a single IP address, the system must determine which SSL certificate to present to the client during the initial TLS handshake. This is achieved using an extension of the TLS protocol called Server Name Indication (SNI).

The configuration logic is as follows:

Profile Type: The Client SSL profile is responsible for terminating the SSL connection from the client (the user) to the BIG-IP system.

The Setting: Within the Client SSL profile (under the "Advanced" view), there is a field specifically called Server Name. By entering the specific hostname (e.g., www.example.com) in this field, the BIG-IP system can match the hostname requested by the client in the ClientHello message to the correct profile.

Implementation: The administrator typically creates multiple Client SSL profiles—one for each hostname—and assigns them all to the same virtual server. One of these profiles must be designated as the Default SSL Profile for SNI to handle requests where the client does not provide a hostname or provides one that does not match any specific profile.

By using the Client SSL profile and the Server Name setting, the BIG-IP system ensures that each user receives the correct certificate for the specific site they are trying to reach, even though all sites share a single virtual server IP.

Application-level monitors ensure that only the affected service is marked down, not the entire node.

F5 provides several pre-configured (built-in) TCP profiles designed to optimize traffic for different network conditions. When an administrator is looking to improve general performance but does not have a specific, narrow use case (like strictly mobile or strictly long-haul WAN), the f5-tcp-progressive profile is the recommended starting point.

The f5-tcp-progressive profile is designed as a modern, high-performance replacement for the older default TCP settings. It incorporates several advanced congestion control algorithms and buffer management techniques that allow it to adapt dynamically to varying network latencies and packet loss scenarios. Unlike f5-tcp-legacy (Option A), which uses older, less efficient stacks, the progressive profile leverages modern TMM (Traffic Management Microkernel) optimizations.

While f5-tcp-mobile (Option B) is highly effective for high-loss cellular networks and f5-tcp-wan (Option D) is optimized for high-latency long-distance links, they can sometimes be too aggressive or poorly suited for standard campus or data center environments. The f5-tcp-progressive profile acts as a "best-of-all-worlds" template that typically provides an immediate performance boost for most web applications by improving window scaling and fast-retransmit behavior. Therefore, it is the procedural "first step" in TCP performance tuning before moving to more specialized, niche profiles.

When a pool contains servers with heterogeneous hardware capabilities (differing CPU, RAM, or connection limits), a static load balancing method like Round Robin is ineffective because it distributes requests equally, regardless of the server's capacity. To optimize traffic distribution for newer, more powerful servers, a dynamic or weighted method is required.

Weighted Least Connections (member): This is the ideal method for this scenario. It combines two factors:

Least Connections: It first checks the current active connection count to ensure traffic goes to the least busy server.

Weight (Ratio): It allows the administrator to assign a "Ratio" value to each pool member. Newer servers can be assigned a higher ratio (e.g., 3) while older servers are assigned a lower ratio (e.g., 1). The BIG-IP system uses these weights to disproportionately favor the newer servers even when connection counts are similar.

Why other options are incorrect:

Global Availability: This is primarily a GSLB (Global Server Load Balancing) or specific LTM priority group concept where traffic is sent to the first available member in a list until it fails, then moves to the next. It does not load balance based on capacity.

Round Robin: This passes each new connection request to the next server in line, treating the old and new servers exactly the same.

Least Connections (member): While this sends traffic to the server with the fewest active connections, it assumes all servers are equal. If an old server and a new server both have 10 connections, they are treated as equally capable of taking the 11th, which is not true in this scenario.

X-Forwarded-For inserts the original client IP into HTTP headers, preserving client identity while SNAT is enabled.

SSH is a TCP-based service. A TCP monitor validates service availability without requiring application-layer inspection.

To solve this requirement, we must distinguish between the two "legs" of an SSL connection in a BIG-IP environment: Client-side and Server-side.

Current State (SSL Bridging): The administrator states the servers currently require encrypted traffic. This means the BIG-IP is likely performing "SSL Bridging." In this setup, a Client SSL profile terminates encryption from the user, and a Server SSL profile re-encrypts the traffic before sending it to the back-end servers.

Target State (SSL Offloading): The requirement is to "offload SSL" to reduce web server load. This means the BIG-IP will continue to handle the encryption for the users (keeping the Client SSL profile) but will communicate with the back-end servers using unencrypted HTTP.

Why Option A is correct:

Remove the Server SSL profile: By removing this profile, the BIG-IP stops attempting to initiate an SSL/TLS handshake with the pool members.

Configure Pool Members to use HTTP: The service port for the pool members must be changed (typically from port 443 to port 80) so that the BIG-IP sends standard HTTP traffic to the servers.

Why other options are incorrect:

B & D: These suggest removing the Client SSL profile. If you remove this, the users can no longer connect via HTTPS, which violates the requirement for encrypted communication between the users and the BIG-IP.

C: Changing the Virtual Server to accept HTTP traffic would mean the user-to-BIG-IP connection is no longer encrypted, which is the opposite of SSL termination/offloading.