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Systems & Data Center · Advanced

Multichassis Link Aggregation (MC-LAG)

A technique that lets a device bundle links to two separate switches as one LAG, as in Juniper MC-LAG or Cisco vPC.

Definition

MC-LAG peers synchronize state over an inter-chassis link (ICL) and control protocol (ICCP on Juniper). It provides active-active redundancy, though EVPN ESI-LAG is now preferred in Juniper fabrics.

Example

Two QFX switches run MC-LAG with ICCP so a server's LACP bond stays up if one switch fails.

Exam tip

MC-LAG is proprietary per vendor and needs an ICL; ESI-LAG is standards-based EVPN multihoming.

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