Coming in OcNOS 7.1 · End-to-end

Global Load Balancing: Fabric-Wide Path Selection

DLB makes the right call at one hop; GLB makes the right call across the whole fabric. Coming in OcNOS 7.1, Global Load Balancing extends load balancing from a per-port view to end-to-end path quality, closing the multi-hop hot-spot gap on three-tier AI fabrics up to the 16,384-GPU ceiling.

Book an architecture review Open the AI fabric design suite
OcNOS 7.1GLB release
End-to-endpath scoring, not local hop
16,384GPU ceiling, reference design

Scoring the whole path, not just the local hop

A three-tier slice (leaf, spine, super-spine) carrying GPU AllReduce. GLB picks the path with the best end-to-end score, not the best local-egress score, so a clean uplink that lands on a congested downlink is no longer chosen blindly.

Global Load Balancing across a three-tier AI fabric Three-tier AI fabric. Two super-spines on top, four spines in the middle, two leaves at the bottom. Telemetry arrows flow upward and back down so the ingress leaf sees end-to-end path quality. One spine-to-super-spine link is congested and bypassed in favour of an alternative end-to-end path. end-to-end telemetry Super-Spine-1TH5 · 51.2T Super-Spine-2TH5 · 51.2T Spine-1e2e ok Spine-2e2e ok Spine-3uplink hot Spine-4e2e ok Ingress LeafGLB · ranks paths Egress Leaftarget rack GLB · END-TO-END PATH SCORING · MULTI-HOP CONGESTION AWARENESS · OcNOS 7.1

DLB and GLB, by scope of the path decision

DLB scores each ECMP next-hop using local egress queue-depth, which is optimal on a 2-tier leaf-spine. Scale to a 3-tier Clos and you can pick a spine with a clean uplink, only to land on a super-spine whose downlink back to the egress leaf is congested. The local view is correct; the end-to-end view is wrong.

Axis DLBlocal, shipping today GLBglobal, OcNOS 7.1
Scope of decisionPer-hop: each switch ranks its own ECMP next-hops.End-to-end: ingress leaves rank complete leaf-to-leaf paths.
Signal usedLocal egress queue-depth and link-utilisation on this switch.Congestion telemetry aggregated from every tier, back to ingress.
Best fit2-tier leaf-spine fabrics, and the leaf-to-spine hop in a three-tier fabric.Three-tier fabrics with super-spines, up to the 16,384-GPU ceiling.
Hot-spot caughtLocal egress congestion only.Downstream hot-spots the local hop cannot see.
RebindingFlowlet-aligned, in-order for RoCEv2 and TCP.Flowlet-aligned, same in-order guarantee, full-fabric input.

How the GLB implementation fits together

GLB is enabled by OcNOS as the network operating system on open Broadcom-based hardware.

Scale

Up to the 16k-GPU ceiling

Reference designs use 256 spine switches and 128 super-spine switches, each a 64x800G Tomahawk 5, sized to the 16,384-GPU architectural ceiling.

What to expect when you adopt GLB

GLB is coming in OcNOS 7.1. Contact IP Infusion for supported platforms and licensing.

  • Coming in OcNOS 7.1. Release life cycle and support windows at the OcNOS releases page.
  • Architecture review available. If you are sizing a 1,000-plus GPU fabric, we will run a sizing exercise that includes the GLB telemetry plane. Get a first-pass leaf-spine layout with the AI fabric design suite.

DLB sets the floor, GLB raises the ceiling

Dynamic load balancing is already reducing tail latency at 2-tier scale. GLB, coming in OcNOS 7.1, carries that same discipline up into the three-tier fabrics where the largest clusters live.

DLB solves the common case

On 2-tier leaf-spine and the leaf-to-spine hop, local dynamic load balancing already removes most ECMP collisions. That is shipping on TH4 and TH5 today.

GLB solves the scale case

GLB, coming in OcNOS 7.1, scores complete paths so the ingress leaf stops chasing a clean uplink into a congested downlink.

Global Load Balancing, answered

How is GLB different from DLB?
DLB scores each next-hop using local egress queue-depth on one switch, which is optimal on a 2-tier leaf-spine. GLB aggregates congestion telemetry from every tier so ingress leaves rank complete leaf-to-leaf paths, catching downstream hot-spots the local view misses on three-tier fabrics.
When is GLB available?
GLB is coming in OcNOS 7.1. Contact IP Infusion for supported platforms and licensing.
How large a fabric does GLB support?
Reference designs use 256 spine switches and 128 super-spine switches, each a 64x800G Tomahawk 5, sized to the 16,384-GPU architectural ceiling.

Go deeper. Take it with you.

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Datasheet

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Sizing a multi-thousand-GPU fabric? Let's run the numbers together

Tell us the workload and the GPU scale, and an IP Infusion engineer will size the GLB telemetry plane with you, or start with a first-pass leaf-spine layout in the AI fabric design suite.

Book an architecture review Open the AI fabric design suite

Design the whole AI fabric with OcNOS

From the business case to the port-count maths, pick up wherever you are in the build.

Solution Open AI Fabric The complete 800G AI fabric: open switches, OcNOS-DC, and support under one contract. Reference designs AI Fabric Topologies Rail-optimized two-tier and three-tier fabrics, and coherent DCI, sized in real port counts. Size & build AI Fabric Design Suite Size a GPU fabric: leaf, spine, and super-spine counts with a component and power summary.
New to AI fabrics? Start here What is an AI fabric? What is a GPU fabric? What is lossless Ethernet? What is RDMA? AI networking switches
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