Glossary · Networking

Link Aggregation (LACP)

Link aggregation bundles several physical network links into one logical link to increase capacity and provide failover, often via LACP.

Updated October 6, 2026

Link aggregation combines multiple physical Ethernet connections between two devices into one logical link. It is standardized as IEEE 802.3ad (now 802.1AX), and its control protocol, LACP (Link Aggregation Control Protocol), negotiates and monitors the bundle. It is also called port channel, bonding or teaming.

Why it matters

A bundle gives more total bandwidth and resilience: if one cable fails, traffic continues on the rest. Spanning tree treats the bundle as one link, so none of its members are blocked. However, a single flow is normally sent over just one member, chosen by hashing addresses and ports, so one download does not go faster than a single link. The gain appears when many flows run in parallel.

Example

Two 1 Gbit/s ports from a file server are bundled to a switch. Ten clients each transferring a file may share about 2 Gbit/s in total, but any one client still tops out near 1 Gbit/s. On Linux:

ip link add bond0 type bond mode 802.3ad
ip link set eth0 master bond0
ip link set eth1 master bond0

The switch ports need matching LACP configuration.

Common mistakes

  • Expecting one connection to use the combined speed.
  • Configuring LACP on one side only, which leaves the links unbundled or causes loops.
  • Mixing different speeds or duplex settings inside one bundle.

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