Load Balancing and Load Sharing - It is important to understand the difference between load balancing and load sharing.
Routing protocols after calculating the routes from their databases , they automatically put equal cost routes into the routing table. Only exception to this behaviour is BGP. Unless you enable multi-path support , BGP doesn’t place equal cost routes into routing table.
EIGRP can place unequal cost paths into routing table in addition to equal cost ones.
For both ECMP and UCMP paths if you check the route information with ‘ show ‘ commands , you will encounter ‘ traffic sharing ‘ values.
Routers will use only routing protocol information based on layer 3 , 4 information will hash the flows and send them always over one link, another flow over different link. Very similar to ‘ round robin ‘ behaviour of the load balancers.
Round-robin load balancing is similar to load-sharing
Let’s imagine server load balancing:
Load balancers can measure the servers resources such as CPU , memory , established session numbers, least connections.Based on those numbers, gives more intelligent decision and redirect to flows to best servers.
Load balancing based on least connection allows intelligent decision
Although we use the term ‘ load balancing ‘ with the routers,switches; it is good to know that the correct term is ‘ load sharing ‘.
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