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What is Link aggregation?

A technique (IEEE 802.1AX) that bundles several physical links so they are treated as one logical link. It increases bandwidth, and if one link fails the remaining links keep carrying traffic. Frames are assigned to one link per flow (such as a combination of source and destination), so a single flow is limited to the speed of one link. LACP is the protocol that automatically aligns the bundling settings at both ends.

Japanese name: リンクアグリゲーション

Link aggregation appears in 1 practice question across 1 topic, including Network Design and Operations.

Field: Network Design and Operations

Try it: questions about Link aggregation

Four 1 Gbps links between two switches are bundled into one logical link with link aggregation. Frames are distributed with the common method that chooses the link for each combination of source and destination addresses and port numbers (each flow). Which is closest to the maximum throughput a single TCP connection can achieve?

  1. A1 Gbps
  2. B2 Gbps
  3. C4 Gbps
Show answer and explanation

Answer: A. 1 Gbps

With link aggregation, frames belonging to the same flow are normally sent over the same single link. Splitting one flow's frames across several links could reorder them and hurt TCP performance. A single TCP connection is therefore limited to one link, 1 Gbps. When there are many flows they are spread over the four links, so up to 4 Gbps can be used in total. If one link fails, traffic continues on the remaining links, and STP sees the bundle as a single link, so none of its member links is blocked.

Link aggregation in the explanations

Questions that mention Link aggregation (1)

  1. Four 1 Gbps links between two switches are bundled into one logical link with link aggregation. Frames are distributed with the common method that chooses the link for each combination of source and destination addresses and port numbers (each flow). Which is closest to the maximum throughput a single TCP connection can achieve?

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Related terms

Throughput TCP (Transmission Control Protocol) Spanning Tree Protocol (STP) ACL (access control list) Administrative distance BGP (Border Gateway Protocol) Broadcast domain Longest prefix match OSPF (Open Shortest Path First) Path MTU discovery

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