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“F5 networks” is a leading multinational conglomerate that specializes in Application Delivery Networking and services. The primary focus of this business is on security, efficiency, accessibility, and distribution. F5 is compatible with public, private, and hybrid cloud systems, including Azure, Amazon Web Services, and Google Cloud. To assist you in the interview process, we have compiled and given below a list of F5 load balancer interview questions that are appropriate for both fresh graduates and experienced applicants. Mastering these interview questions can help you gain confidence and pass your interview.

F5 Load Balancer Interview Questions and Answers

F5 Load Balancer Interview Questions For Freshers

1. What is Load Balancing on Servers?

Server Load Balancing (SLB) optimizes network speed and content delivery by utilizing a variety of techniques and prioritization to react to network requests. SLB allocates users to a set of servers and guarantees that users are not routed to failing servers.

2. How does SLB function?

SLB utilizes two distinct forms of load balancing:

  • Application-level load balancing: balancing choices are made using traffic data, including WSLB.
  • Load balancing at the transport level: this is a DNS-based method that does not require an application payload.

3. Is an F5 load balancer a software application or a hardware device?

To begin, load balancers are classified as software-based and hardware-based. Vendors of hardware such as F5 Networks and Citrix include the software-based load balancer within their products.

4. What information is required to configure the appliance for cookie load balancing?

You'll need the cookie's name and value, the VIP to which you're binding, and the groupings to which you're balancing.

5. What is a load balancer's health check?

The load balancer's Health Check function enables you to configure settings for doing diagnostics on the functionality of web servers connected with each appliance. Health checking enables you to ascertain whether a server or resource is operational or has failed.

6. What are the three applications of SLB?

The three advantages of utilizing SLB are as follows:

  1. Increased scalability.
  2. It provides redundancy.
  3. Upkeep and performance.

7. How familiar are you with iControl?

iControl is a web service-enabled Application Programming Interface that provides granular control over F5's application administration and customization platform.

8. What exactly is GSLB?

Global Server Load Balancing is quite similar to SBL, except that it enables us to load balance VIPs from many geographical locations as a single entity. Additionally, GSBL enables geographic site expansion and low latency.

9. What is the procedure for enabling GSLB?

The easiest method of enabling GSLB is through the use of CDN (Content Delivery Network). Global CDN will collect data from their clients' origin servers, cache it on geographically distributed servers, and offer dependable internet content to consumers worldwide.

10. What are persistent cookies?

Typically, persistent cookies are retained on the user's device. These cookies enable us to remember our users' credentials, as well as information, preferences, and settings. Essentially, these cookies are used to enhance the user's online experience.

11. In an array network load balancer, what is the distinction between a persistent cookie strategy and a QoS cookie policy?

The Persistent Cookie strategy assigns a cookie to a group depending on its name. A QoS Cookie policy determines the server group to which a cookie is assigned depending on the identity and value of the cookie issued to that unit.

12. Which server will be contacted first when load balancing to the main server?

This is determined by the load balancing strategy you choose. Following are a few examples:

  • Least Connection Method: The genuine server with the fewest simultaneous connections will obtain the initial connection.
  • Round Robin Method: The authenticated server with the smallest entry index receives the initial connection.
  • Shortest Response:  The user request will be routed to the most responsive actual server.

F5 Load Balancer Interview Questions For Experienced

13. What is a Reverse Proxy Cache?

Reverse Proxy Cache is a caching that resides next to the source server, as the name implies. When a user requests a cached item, the proxy will respond from the cache rather than the origin server.

14. Is it necessary to enable clustering in order to access GSLB?

Yes, the clustering must be enabled in order to leverage GSLB. Each proxy in the network should have a configuration that is similar. As a result, if an appliance becomes a zone master, it may act as a DNS.

15. What Is Overflow?

When there are more queries than the server can handle, this is referred to as Overflow. Overflow is one of the techniques in array GSBL that addresses this issue by redirecting queries to another server when the local site reaches 80% of its capacity.

16. What is the purpose of the "least connections" method?

The "least connections" approach directs clients to sites with the fewest contemporary links.

17. What is the purpose of a round-robin load-balancing algorithm?

Round-robin is one of the most straightforward ways for spreading client requests over a set of servers. As each query is sent to one of the group's servers, this protocol instructs the load balancer to continue the procedure until no more queries are received.

18. Describe the various load balancing strategies.

Various load balancing strategies include the following:

  • Round-robin Format
  • Round Robin with a weighted distribution
  • Weighted Least Common Denominator Connection
  • SDA Resource-based approach
  • Adaptive Resource-Based Adoption
  • Weighted Response Time

19. In F5, what is a pool?

A pool is a collection of equipment, such as web servers, that work together to collect and handle the traffic. BIG-IP does not route client information to the specified destination IP address in the user requests. Rather than that, it transmits the request to the subscribers of that group.

20. What purpose do the nodes in your load balancer serve?

The load balancer's nodes will assist you in routing customer queries to the specified destination. In basic terms, the node serves as a conduit for the client’s request to reach its destination.

21. What are the distinctions between dynamic and static content? Is it possible for the Array appliance to cache dynamic content?

A web server responds to a client's request for a web page by returning the required content. Static content is that which is obtained from disk/memory and provided to the user without further intervention.

Dynamic content is determined by measuring the amount that is created on the fly by the host.

22. What is the depth of recursion?

It represents the number of layers accessible underneath the primary or parent page.

23. What is the definition of True Clustering?

True clustering enables the synchronization of all configurations across all machines in the cluster. Of course, only universal parameters are synced, such as the SLB configuration. Local characteristics, such as the IP addresses of the interfaces, are not synced.

24. What is the definition of Virtual Clustering?

Virtual clustering ensures the availability of VIPs between cluster members. For instance, if one appliance responsible for traffic processing fails, another device in the cluster will assume responsibility for traffic processing.

25. What is virtual clustering and how does it work?

In a group of Array equipment, one device is designated as the Master for a certain VIP and is responsible for all traffic associated with that VIP. All others remain in Backup mode. If the Master device fails, one of the Backup devices is promoted to Master status.

F5 Load Balancer Technical Interview Questions

26. What is RAM cache?

The RAM cache is used to provide information to clients straight from the memory of the F5 device. Both client and the server benefit from the RAM cache since it decreases the load on the server and responses delay.

27. What is the content of the RAM Cache that is not cacheable?

Private data supplied in the cache's management headers is not cacheable.

28. How can you delete the cache quickly?

The shortcut key combination ctrl+F5 is used to refresh or delete the cache.

29. What is pipeline construction?

Pipelining is a mechanism in which several requests are sent simultaneously over a single TCP protocol without anticipating answers. The server will provide replies in the order in which they were received.

30. What parameters do we need to provide while configuring the cluster?

The following are the parameters that must be defined in the cluster configuration:

  • Address of the VIP
  • Cluster-ID
  • Method of Authorization
  • User Interface
  • Priorities.

31. What exactly is SNAT?

SNAT translates the source client's IP address included inside the query to the BIG-IP device's transcription address.

32. Define DNAT?

Destination Network Address Translation is abbreviated as DNAT. This enables users to route packets to a specified IP address.

33. What exactly is an iRule?

It is a type of script that was developed to access features that are not available through the GUI or CLI. This iRule enables us to engage directly with the traffic flowing by that device.

34. What are the various components of iRule?

iRule contains three critical components:

  • Operators
  • Declarations of Events
  • Commands for iRule.

35. Is it possible to distinguish between verified and unverified exceptions?

We can inspect verified exceptions during a program's execution, whereas we can inspect unverified exceptions during the program's compilation. Exceptions can be produced manually, both controlled and uncontrolled.

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Liam Plunkett

Solution Architect

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