https://www.techtarget.com/searchnetworking/answer/Application-vs-network-load-balancing-Whats-the-difference
None of the services users take for granted on the internet -- such as online shopping, reading the news or checking investments -- or in large corporate IT environments would work without load balancing.
Load balancing spreads traffic over multiple systems that might be geographically distributed in clouds or data centers and located in virtual servers or dedicated systems worldwide. For example, without load balancing, everyone who checked a news website or shopped online would access the same system. If all that traffic flowed into any single system, the servers would become hopelessly bogged down. Load balancing directs that traffic among servers so they share the load more evenly.
Two common types of load balancing are network load balancing and application load balancing. Each differs by whether it operates at Layer 4 or Layer 7 of the seven-layer OSI model.
Network load balancing is implemented in a system or device that operates similarly to a router, often with hardware and software designed specifically for the purpose. It operates at Layer 4, the transport layer, and supports protocols such as TCP and User Datagram Protocol (UDP). TCP guarantees all packets are delivered, while UDP makes no guarantees.
End users make requests to services using commonly known domain names. For example, a request to CNN's website goes to the load balancer identified by the site's internet address. The load balancer's routing table is configured with multiple IP addresses of systems loaded with CNN content. The balancer performs a quick operation, forwarding the request to the appropriate system.
A network load balancer doesn't examine the request's content, so it doesn't decide where to direct the request based on the content. If a server goes offline, a load balancer skips the route to it, providing overall reliability.
Application load balancing operates at Layer 7, the application layer. An application installed on a server examines each incoming request, such as HTTPS or SMTP requests. Application load balancing can direct requests toward one of the servers best able to satisfy the request. For example, an online shopping request could be directed to a system maintaining the inventory for that type of product.
While a network load balancer forwards requests, application load balancing examines the application layer protocol data from the request header. This examination takes more time than network load balancing, but it enables the balancer to make a more informed decision about where to direct the request.
As requests arrive, load balancers use different algorithms to choose possible routes. Some algorithms are static, meaning they route requests according to predefined rules, while others are dynamic and make routing adjustments based on factors such as server workloads and response times. Examples of commonly used load-balancing algorithms include the following:
Network load balancing and application load balancing each have advantages, depending on the type of internet service required. Network, or Layer 4, load balancers can provide faster responses, as they forward requests without examining them. Application, or Layer 7, load balancers offer greater overall efficiency because they send requests where they are most efficiently handled.
The choice of network or application load balancing depends on the type of information stored in web applications, cloud environments and on-premises systems, as well as the reason people access it and the level of traffic.
Using CNN again as an example, users typically go to its website for the latest news. Some click on a specific story, while others see what's on the homepage and select a story from there. Application load balancing wouldn't be useful in the latter scenario because the requests are simply to CNN.com and don't include information on the individual stories users will choose. The required routing of requests to different servers for performance optimization is a task for a network load balancer.
On the other hand, requests to Amazon's website by online shoppers often involve a particular type of product. Application load balancing would be useful in this case. Directing an initial request to a server that supports the product type a shopper is interested in should help speed up the response.
A wide variety of load balancers are available to buy or for free. Some offer just application or network load balancing, while others support both types. The following are some examples of popular commercial products, listed in alphabetical order:
Open source load-balancing tools with free editions include HAProxy, Relianoid and Traefik Proxy. Some commercial products, such as Progress Kemp LoadMaster, also include a free version, while others can be used free for evaluation or a limited time.
David Jacobs has more than 30 years of networking industry experience. He has managed leading-edge hardware and software development projects as well as consulted Fortune 500 companies and software startups.
03 Apr 2025