The Open Systems Interconnection (OSI) Reference Model for networking outlines the various layers where load balancing can be performed. Layer 4, known as the Transport layer offers end to end connections and reliability.
When studying layer 4 load balancing it is natural to also compare the Layer 7 load balancing options as well. Layer 4 load balancing is relatively simple while layer 7 load balancing is far more complex. For this reason Layer 4 load balancers are normally available free of charge. One of the best known Layer 4 load balancers is Microsoft Network Load Balancer or NLB, this is a core network load balancer software that is available to users of mission critical Microsoft applications including Microsoft Exchange and Microsoft OCS the unified communications platform. Like other Layer 4 load balancer solutions it is fairly simple and most try to replace NLB with a more complex load balancer. At Layer 4, a load balancer has visibility on network information such as application ports and protocol (TCP/UDP). The load balancer delivers traffic by combining this limited network information with a load balancing algorithm such as round-robin and by calculating the best destination server based on least connections or server response times.
Most layer 4 load balancers perform the following functions: * Load balances at the most simplistic level and directs traffic based on server response time
Layer 7 load balancing is more complex but far more efficient
At Kemp we have combined the simplicity of Layer 4 load balancing with the content sensitive and rich options offered by layer 7 load balancing.
To gain an even greater level of understanding about layer 4, why not deploy a trial license today and configure layer 4 virtual services.