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Load-Sharing vs Load-Balancing

Load balancing is an attempt to process traffic evenly across a network with multiple links. The reason this term is less preferred than load sharing is because it is difficult to achieve perfect load balancing. With load balancing, if I looked at two traffic graphs, I’d expect to see two identical amounts of bandwidth being used on each path to the destination.  Because of the different ways I can achieve load balancing (eg: with cef I could use per-packet, per-destination, per source-destination etc) it can be difficult to achieve true load balancing across each of the paths.

Load sharing is a term used when attempting to share some of the traffic across multiple links.  A good example of load sharing is when having two devices connect using two links of different speed.  Let’s say link one is 9Mbit/s, and the other is 3Mbit/s.  For every three packets we send through the 9Mbit link, we would want to send one packet down the 3Mbit/s link.  The result is that the 9Mbit/s link would send a higher proportion of traffic than the 3Mbit/s link.

There is one more point I want to add before moving on.  When talking about either term, load balancing or load sharing, we are talking about a unidirectional method of sharing data through paths to the destination.  This is because network layer traffic (layer 3 IP traffic) is connectionless; meaning that each packet that is sent, is a completely independent piece of data.  So return traffic can take a totally different path to which is was sent.  If we want to load-balance or load-share back to the source, we would have to configure this separately.

2 Comments

ccna certificationMay 18th, 2012 at 12:40 pm

Load-sharing and Load-Balancing is easily one of the most misunderstood topics in networks. Those knowledgable usually understand the difference and is aware of the concept of load-sharing.

karthikFebruary 3rd, 2016 at 1:54 pm

As per my understanding Load balancing occurs only when the threshold reaches it’s level,

and load-sharing occurs when the both link are being utilized at the same time.

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