What is Load Sharing?

Understanding Load Sharing

Load sharing is a networking technique that distributes traffic across multiple available paths, links, or servers at the same time to optimize resource use, prevent any single component from becoming a bottleneck, and improve availability. Unlike strict failover, load sharing actively uses all paths simultaneously rather than holding some in reserve.

The mechanism distributes flows based on attributes such as source and destination IP, port, or a hash of packet headers, keeping individual sessions on a consistent path to avoid reordering. Routing protocols like OSPF and EIGRP support equal-cost (and, with EIGRP, unequal-cost) multipath; link-aggregation technologies bundle physical links; and server load balancers spread connections across a pool. The distribution is typically per-flow rather than per-packet to preserve session integrity.

Load sharing matters for availability and resilience, which support the availability pillar of the CIA triad. By spreading workload, it prevents overload-induced outages and absorbs traffic spikes, including some of the impact of volumetric denial-of-service attacks. It also adds redundancy: if one path or server degrades, capacity remains on the others. Without it, a single congested link or saturated server can become a single point of failure that takes services down.

For example, a data center with two equal-cost WAN links to a provider can configure ECMP so that outbound flows are hashed across both circuits. Traffic uses the full combined bandwidth during peak periods, and if one circuit fails, the remaining link continues carrying traffic, though at reduced capacity, keeping critical services reachable.