Differences between Windows Clustering Network Load Balancing and Round Robin?

Answer 1

I will make a few assumptions here: 1) By "Windows Clustering Network Load Balancing" you mean Windows Network Load Balancing software included in Windows Server software a.k.a NLB., and 2) By Round Robin, you mean DNS Round Robin meaning the absence of a software or hardware load balancing device, or the concept of the Round Robin algorithm available in just about every load balancing solution.

Microsoft NLB is designed for a small number (4 - 6) of Windows Servers and a low to moderate number of new connections per second, to provide distribution of web server requests to multiple servers in a virtual resource pool. Some would call this a "cluster", but there are suttle differences between a clustered group of devices and a more loosely configured virtual pool. From the standpoint of scalability and performance, almost all hardware load balancing solutions are superior to this and other less known software load balancing solutions [e.g. Bright Tiger circa 1998].

DNS Round Robin is an inherent load balancing method built into DNS. When you resolve an IP address that has more than one A record, DNS hands out different resolutions to different requesting local DNS servers. Although there are several factors effecting the exact resulting algorithm (e.g. DNS caching, TTL, multiple DNS servers [authoritative or cached]), I stress the term "roughly" when I say it roughly results in an even distribution of resolutions to each of the addresses specified for a particular URL. It does not however, consider availability, performance, or any other metric and is completely static. The basic RR algorithm is available in many software and hardware load balancing solutions and simply hands the next request to the next resource and starts back at the first resource when it hits the last one.

NLB is based on proprietary software, meant for small groups of Windows servers only on private networks, and is dynamic in nature (takes into account availability of a server, and in some cases performance). "Round Robin", DNS or otherwise, is more generic, static in nature (does not take into account anything but the resource is a member of the resource pool and each member is equal), and ranges from DNS to the default static load balancing method on every hardware device in the market.