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Spectrum-X course/1. Foundations/Lesson 1.2

Choosing the switch: SN2201 through SN6800-LD

S1·E2The switch that cannot be installed · Hotel lobby, 07:20, an hour before the design review

S1·E2Understand~30 minsources checked todayverified against Dell-hosted SN5600 and SN2201 datasheets, Dell PowerSwitch SN6000 spec sheet, SN5000 ordering information, Dell AI switches page, Cumulus Linux 5.18 What's New, re-fetched 2026-09-07

Builds on: What Spectrum-X is, and what it is not

Before you read: what do you already know?

3 quick questions. Wrong answers are fine and expected; trying first makes the lesson stick.

After this lesson you can

  • Match each Spectrum switch model to its ASIC generation, port count, aggregate bandwidth and packet buffer.
  • Explain the four non-networking constraints that decide a switch choice: airflow direction, power feed, cooling medium and ambient ceiling.
  • Read an SN5000 ordering part number and say what its suffix commits the customer to.
  • Identify where the NVIDIA and Dell datasheets disagree and state both figures instead of picking one.

Episode 2 — The switch that cannot be installed

The situation · Hotel lobby, 07:20, an hour before the design review

The bill of materials is open on the SE’s laptop and his coffee has gone cold again. Thirty-two liquid-cooled Spectrum-6 leaves, priced overnight, about to be quoted into the hall you both walked yesterday: AC power distribution units, no busbar, no facility water, and an inlet you measured at 34 C. Procurement joins early and asks only about lead time, which this once is the right question.

You do the elimination out loud before anyone else arrives. The -LD models take a 48/54 VDC busbar and facility water at 17-45 C through UQD8 v2 quick disconnects, none of which that room has.[5] The air-cooled SN6600 exists, but its operational ambient stops at 0-30 C, ASHRAE A3 - tighter than the hall already runs.[5] The SN5600 goes to 35 C and the SN5610 to 40 C.[1] Then the quiet one: airflow direction is baked into the ordering part number, only the SN5400 is listed in both directions, and a mis-ordered chassis cannot be corrected on site.[4]

This is why the portfolio is shaped the way it is. A generation is silicon - 51.2 Tb/s per Spectrum-4 ASIC, 102.4 Tb/s per Spectrum-6 - but a model is a chassis with a power feed, a cooling medium, an ambient ceiling and a direction the air travels.[1][5]

The rack eliminates models faster than the network chooses them.

Segment 1 starts where the choice really starts: the ASIC.

1Three ASIC generations, and what each one buys

The portfolio a Dell rep quotes spans three Spectrum generations. Spectrum (the SN2201 generation) carries a 16 MB buffer and up to 256,000 shared forwarding entries.[7] Spectrum-4 is described as “the fifth-generation Ethernet switch ASIC”, with “a fully shared and monolithic packet buffer across all ports, supporting cut-through traffic from all ports”, a deep parser and editor that “can process payloads up to the first 512 bytes”, single-pass VXLAN routing and bridging, and “up to 512,000 entries to be dynamically shared” across MAC, ARP, IPv4 routes, ACLs, ECMP and VXLAN tunnels plus 512,000 on-chip flow counters.[1] Spectrum-6 delivers “102.4 Tb/s aggregate bandwidth per ASIC”, is “built on 200G SerDes” with “800 Gb/s per port”, and supports 750,000 entries shared across routes, MAC and ACL.[5][6]

The generation also sets the feature floor for the rest of this course: adaptive routing, packet trimming, high-frequency telemetry and latency monitoring are Spectrum-4-and-later features, so a Spectrum-3 SN4700 in the same rack is a perfectly good switch that cannot run the Spectrum-X mechanisms.[14]

ProductSpeedPCIeRoleGPU generation
NIC
SuperNIC (no Arm)
SuperNIC (no Arm)
DPU
DPU
SuperNIC (Arm inactive)
DPU / storage processor
Ethernet switch
Ethernet switch
InfiniBand switch
InfiniBand switch

⚠ = not confirmed on a fetched primary source (hover for why). Facts as of DOCA 3.5.0 (Sep 2026). Selections are saved.

Products tab. The two switch rows - Spectrum-4 (SN5600) and Spectrum-6 (SN6600/SN6800) - sit next to the SuperNIC rows on purpose: a Spectrum-X quote is always one switch row plus one NIC row.

2SN5000: the Spectrum-4 workhorses

SN5610 SN5600 SN5600D SN5400
Connectors 64 OSFP 800GbE + 2 SFP28[1] 64 OSFP 800GbE + 1 SFP28[1] 64 OSFP 800GbE + 1 SFP28[1] 64 QSFP-DD 400GbE + 2 SFP28[2]
Capacity 51.2 Tb/s[1] 51.2 Tb/s[1] 51.2 Tb/s[1] 25.6 Tb/s[2]
Packet rate 33.3 Bpps[1] 33.3 Bpps[1] 33.3 Bpps[1] 33.3 Bpps[2]
Lanes per port 8x 100G PAM4[1] 8x 100G PAM4[1] 8x 100G PAM4[1] 8x 50G PAM4[2]
Buffer 160 MB[1] 160 MB[1] 160 MB[1] 160 MB[2]
CPU / memory / SSD Octa-core AMD, 32 GB, 80 GB NVMe[1] Hexa-core x86, 32 GB, 160 GB SATA-3[1] Hexa-core x86, 32 GB, 160 GB SATA-3[1] see SN5000 sheet[2]
PSU / fans 4 (2+2), 5 (N+1)[1] 2 (1+1), 4 (N+1)[1] 2 (1+1), 4 (N+1)[1] 2 (1+1)[2]
Power input 200-240 VAC[1] 200-240 VAC[1] DC bus bar 40-60 VDC[1] AC[2]
Airflow Reverse[1] Reverse[1] Reverse[1] Reverse and forward[2]
Operating 0-40 C[1] 0-35 C[1] 0-35 C[1] 0-35 C[2]

The hardware manual sums the family up as “64 ports of 800GbE in a dense 2U form factor” for SN5600, SN5600D and SN5610, and “64 ports of 400GbE” for the SN5400.[3] NVIDIA’s stated reason for the SN5610 is that it “introduces a modified hardware specification that optimizes system power consumption and enhances efficiency” while “sharing identical scale and connectivity capabilities with the SN5600”; the SN5600D “features a direct current (DC) bus bar for power intake, making it ideal for NVIDIA DGX SuperPOD offerings”.[1] The SN5600 datasheet also claims 256-way ECMP, against 64-way on the SN2201.[1][7]

Cumulus Linux tracks these as separate platforms: 5.13 added the SN5600D and listed SN5400 ITU-T G.8273.2 Class C compliance, and 5.13.1 added the SN5610.[11]

3SN6000: liquid, busbar and photonics

The Spectrum-6 line is where the physical plant starts making the decision. Dell’s spec sheet gives four models.[5] The SN6800-LD is “the industry’s first 4-ASIC co-packaged Ethernet switch for AI scale-out”, with 512 ports of 800 Gb/s over MMC-12 optical fibres, 409.6 Tb/s of capacity, up to 2,048 breakout connections, 5RU, 16-core AMD CPU, 64 GB DDR5, 4x 160 MB of buffer, 64 external laser sources, liquid cooling through 10x UQD8 v2 connectors at 12.27 LPM with coolant at 17-45 C, on a 48/54 VDC busbar (permissible 40-60 VDC).[5] The SN6810-LD is the single-ASIC 2RU version: 128 co-packaged 800 Gb/s ports, 102.4 Tb/s, 4x UQD8 v2 at 3.27 LPM, 16 external laser sources.[5] The SN6600-LD keeps pluggable optics - “64 OSFP cages supporting 128 ports of up to 800 Gb/s in a compact 2RU form factor” - with 2x UQD8 v2 at 5.7 LPM and the same busbar.[5] The SN6600 is the only air-cooled member: AC powered at 220-240 VAC, 3RU, “connector-to-power (port-side intake)”, 256 MB of packet buffer on Dell’s sheet, and an operational ambient of “0 to 30 C, ASHRAE A3”.[5]

Every SN6000 has a dedicated BMC port on RJ45; the BMC is “an integral part of the security Root-of-Trust”, supports remote power management and “reports liquid leak detection events”.[5] Co-packaged optics come with their own claims - 5x higher power efficiency, 10x greater reliability, 5x longer uptimes - and their own dependency, an external laser source that “delivers continuous light to the integrated optical engines”.[6]

Two sheets, two answers on the same model: Dell lists the SN6600-LD with 32 GB DDR5 and an 80 GB NVMe, while the NVIDIA-branded sheet lists 64 GB and 160 GB NVMe.[5][6] Give the customer both numbers with their sources rather than choosing.

4SN2201: the switch everybody forgets to quote

Every AI pod needs an out-of-band network, and NVIDIA positions the SN2201 as “ideal as an out-of-band (OOB) management switch or as a ToR switch connecting up to 48 1G Base-T host ports with non-blocking 100GbE spine uplinks”.[7] Its specification is deliberately modest: 48x RJ45 plus 4x QSFP28, 448 Gb/s throughput, 667 Mpps, 16 MB packet buffer, dual-core x86 with 8 GB of memory and a 20 GB SSD, two power supplies in 1+1, four fans in N+1, forward or reverse airflow, 100-264 VAC input and 100 W typical ATIS power in a 1U chassis.[7] Port options are 4x100GbE, 8x50GbE, 4x40GbE, 16x25GbE, 16x10GbE, 16x1GbE and 48 Base-T ports at 1000, 100 or 10 Mb/s.[7] The hardware manual adds an SN2201_M variant that takes a DC power busbar instead of the two PSUs.[8] The datasheet claims 64-way ECMP, and the switch supports ONIE, Cumulus Linux and community SONiC.[7]

Dell resells all of this. Its AI-switches catalogue lists PowerSwitch SN6800-LD (409.6 Tbps), SN6810-LD (102.4 Tbps), SN6600-LD (102.4 Tbps), SN5610 (51.2 Tbps), SN5600D (51.2 Tbps), SN5400 (25.6 Tbps), SN4700 (12.8 Tbps) and SN2201 (448 Gbps), alongside the Broadcom-based Z9864F-ON, Z9664F-ON and Z9432F-ON and the Quantum InfiniBand models.[9] Lesson 5 works out who supports what.

5Reading the ordering table before the quote goes out

Model choice ends in a part number, and the SN5000 ordering table carries commitments that no software setting can undo.[4] The SN5400 ships as 920-9N42C-00RB-7C0 (64 QSFP56-DD + 1 SFP28, AC PSUs, C2P airflow) and 920-9N42C-00FB-7C0 (64 QSFP56-DD + 2 SFP28, AC PSUs, P2C airflow) - two airflow directions, two part numbers.[4] The SN5600D is 920-9N42F-00RI-KC0 with the 48 VDC busbar, and the SN5610 is 920-9N42F-00RI-3C1 with four AC PSUs.[4] The AC SN5600 920-9N42F-00RI-7C0 is marked End of Life in that table while the other rows are in production release.[4]

The line that went out at noon

How it ended

The revised quote is SN5610 leaves at 51.2 Tb/s, ordered with the airflow direction that matches the hall’s hot aisle, plus one SN2201 for the out-of-band network nobody had costed.[1][4][7] Two things you refuse to smooth over go in the same mail: the Dell and NVIDIA SN6000 sheets disagree on memory and SSD, and the AC SN5600 part number is marked End of Life.[5][4] What you say in the review: “Tell me about water, busbar, ambient and aisle direction, and I will tell you which models are even installable in your room.” The SE moves four rows of his promise spreadsheet from Promised to Verified. At 02:10 the night shift calls from the Dell lab, where the pilot rack is being built: twenty-four host links up, eight refusing.

Lab

Read-only. There is no Spectrum switch in the Dell lab, so the hardware half of this lesson is the rack, not the box.

  1. Inventory the lab rack physically. Record: the direction of the hot aisle relative to the port side of the servers, whether the rack has AC PDUs or a DC busbar, the measured inlet temperature, and whether any liquid loop exists. No commands, no changes.
  2. Using the ordering table, write which SN5400 OPN would be orderable for that rack and why, then state what would have to change in the room before an SN6600-LD could be installed - water at 17-45 C, UQD8 v2 connectivity and a 48-60 VDC busbar.[4][5] Expected: a two-paragraph note you could paste into a design review.
  3. On a Dell lab host, record the optics you actually have, because that constrains which switch ports they can land on: 
    sudo ethtool -m ens1f0np0 | head -20
    Expected: identifier, connector type and vendor. If the command fails with Cannot get module EEPROM information, the interface is a DAC without EEPROM access or the driver does not expose it - note that and continue.
  4. Optional, customer or partner lab with a live SN switch. Read the platform inventory and environment, no changes: 
    nv show platform
nv show platform environment
    Expected: model string, serial, PSU and fan status, temperatures. Compare the PSU and fan counts with the datasheet row you built in step 1 - a 2+2 PSU count says SN5610, a 1+1 says SN5600 or SN5600D.[1]

Retrieval check

10 questions from memory. Answer before looking anything up; misses become flashcards.

Explain it to a Dell SE

Explain to a Dell rack integrator in four sentences why the switch model in an AI pod is decided by the rack before it is decided by the network.

14 flashcards for this lesson — 0 in deck. Spaced review lives at /review.

Sources

Facts in this lesson were checked against Dell-hosted SN5600 and SN2201 datasheets, Dell PowerSwitch SN6000 spec sheet, SN5000 ordering information, Dell AI switches page, Cumulus Linux 5.18 What's New, re-fetched 2026-09-07. Dates are when each page was fetched.

  1. NVIDIA Spectrum SN5600 Series Switches Datasheet (Dell-hosted) · fetched 2026-09-07
  2. NVIDIA Spectrum SN5000 Series Switches Datasheet (SN5400 columns) · fetched 2026-09-07
  3. Introduction | NVIDIA Spectrum-4 SN5000 2U Switch Systems Hardware User Manual · fetched 2026-09-07
  4. Ordering Information | NVIDIA Spectrum-4 SN5000 Switch Systems · fetched 2026-09-07
  5. Dell PowerSwitch SN6000 Ethernet Switch Series spec sheet · fetched 2026-09-07
  6. NVIDIA Spectrum SN6000 Ethernet Switch Series Datasheet · fetched 2026-09-07
  7. NVIDIA Spectrum SN2201 Switch Datasheet (Dell-hosted) · fetched 2026-09-07
  8. Introduction | SN2201 and SN2201_M 1G Management Switch Systems User Manual · fetched 2026-09-07
  9. AI Networking Switches | Dell USA · fetched 2026-09-07
  10. What's New | Cumulus Linux 5.18 · fetched 2026-09-07
  11. What's New | Cumulus Linux 5.13 · fetched 2026-09-07
  12. Cumulus Linux 5.18 Release Notes · fetched 2026-09-07
  13. NVIDIA Spectrum-X Ethernet Platform · fetched 2026-09-07
  14. High Frequency Telemetry | Cumulus Linux 5.18 · fetched 2026-09-07

The same idea elsewhere

Other lessons that cover this ground, sometimes from another course's angle.