Link Aggregation (LAG / LACP)
Definition
Link aggregation combines several physical links between two devices into one logical link, called a LAG, for more total capacity and resilience. LACP (Link Aggregation Control Protocol), first defined in IEEE 802.3ad and now maintained in IEEE 802.1AX, negotiates and monitors the bundle. Traffic is distributed per flow by a hash of addresses or ports, and not per packet, so that the frames of one flow stay in order. A single flow, such as one Dante or NDI stream, therefore never exceeds the speed of one member link: a 4×1 Gbps LAG cannot carry a single 3 Gbps stream.
In the field
A LAG raises the aggregate capacity available to many parallel flows, not the capacity available to one flow. A single stream that needs more than 1 Gbps requires a faster link, such as 10 GbE. When one member link fails, LACP removes it from the bundle and the remaining links carry the traffic at reduced capacity.
Sources
- IEEE 802.1AX-2020, Link Aggregation : groupe d'agrégation de liens (LAG) utilisé comme un lien unique ; protocole LACP · standards.ieee.org
- Cisco, 10GBASE SFP+ Modules Data Sheet : liens 10 GbE en modules SR, LR, ER et câbles cuivre twinax (DAC) · cisco.com
- Link aggregation (Wikipedia, pointeur secondaire) : LACP défini d'abord dans l'IEEE 802.3ad puis dans l'IEEE 802.1AX depuis 2008 ; répartition par conversation (hachage des adresses) · en.wikipedia.org