MSN4600-CS2RC vs MSN4600-CS2FC: C2P or P2C Airflow?
TL;DR
MSN4600-CS2RC and MSN4600-CS2FC are the same NVIDIA Spectrum-3 SN4600C switch — 64 QSFP28 ports of 100GbE, Cumulus Linux, dual AC power supplies — differing only in the direction air moves through the chassis. CS2RC is C2P (air enters at the ports); CS2FC is P2C (air enters at the power-supply side). Airflow is fixed at manufacture, so the choice is determined by which side of the switch faces your cold aisle.
On this page
The two part numbers are the same switch
Every specification that appears on a datasheet is identical between these two part numbers. Same Spectrum-3 ASIC, same 64 QSFP28 ports at 100GbE, same 6.4 Tb/s of switching capacity, same 2U chassis, same x86 control plane, same dual hot-swap AC power supplies, same Cumulus Linux.
The only difference is which direction the fans push air:
- MSN4600-CS2RC —
R= C2P ("connector to power"). Air enters at the port side and exhausts at the power-supply side. - MSN4600-CS2FC —
F= P2C ("power to connector"). Air enters at the power-supply side and exhausts at the port side.
That is the entire delta. It is also the difference that most often sends a switch back, because nothing on the spec comparison flags it as a decision.
| MSN4600-CS2RC | MSN4600-CS2FC | |
|---|---|---|
| NVIDIA SKU | 920-9N302-00R7-0C0 | 920-9N302-00F7-0C2 |
| Airflow | C2P — intake at ports | P2C — intake at power supplies |
| Platform | Spectrum-3 SN4600C | Spectrum-3 SN4600C |
| Ports | 64× QSFP28 · 100GbE | 64× QSFP28 · 100GbE |
| Switching capacity | 6.4 Tb/s | 6.4 Tb/s |
| Operating system | Cumulus Linux | Cumulus Linux |
| Power supplies | 2× AC, hot-swap | 2× AC, hot-swap |
| Form factor | 2U, standard depth | 2U, standard depth |
Why airflow direction matters
Data centers are organized into hot aisles and cold aisles. Cold supply air is delivered to one face of the rack, equipment pulls it in, and heated exhaust leaves into the opposite aisle, where it returns to the cooling plant. The containment only works if every device in the rack moves air the same way.
A switch installed with reversed airflow breaks that in two directions at once. It ingests hot exhaust from the aisle it should be venting into — so it runs hot, throttles fans to maximum, and shortens component life — and it dumps its own exhaust into the cold aisle, raising intake temperature for every other device drawing from that face. One reversed 2U switch is enough to create a hot spot that reads as a cooling fault somewhere else entirely.
This is why airflow is a purchasing decision rather than an installation detail. Fan modules and power supplies on these platforms are keyed and marked by airflow direction, and a chassis is built as one or the other. You cannot reverse a C2P unit into a P2C unit by turning fans around, and mounting the switch backwards to fix the airflow puts the ports on the wrong face and generally will not reach the cabling anyway.
How to choose the right variant
The rule is simple once it is stated in terms of your own rack rather than the vendor's label:
- Find which face of the rack receives cold supply air. This is the cold aisle, and it is the side every device in that rack must draw from.
- Determine which side of the switch will face it once the switch is mounted the way its ports need to be cabled.
- If the port side faces the cold aisle, order C2P —
MSN4600-CS2RC. Air enters at the ports, which is where the cold air is. - If the power-supply side faces the cold aisle, order P2C —
MSN4600-CS2FC. - Match every other device in the rack. The correct answer for this switch is whatever direction the servers and other switches in the same rack already move air.
When a rack is already populated, step 5 short-circuits the whole exercise: look at what is installed and match it. Mixed airflow in one rack is the failure mode this decision exists to avoid.
Checking what you already have
Units are physically marked — vendors color-code fan and power-supply handles by airflow direction — but the marking convention differs between generations and manufacturers, so it is a confirmation rather than a source of truth.
The ordering part number is the authority. Read the R or F position in the OPN, or the NVIDIA SKU: 920-9N302-00R7-0C0 is the C2P build, 920-9N302-00F7-0C2 is the P2C build. On a live switch the operating system will also report platform and airflow, which is the most reliable check available without opening the rack.
On secondary-market purchases, confirm the OPN against the physical unit rather than the listing. Listings routinely quote the platform name (SN4600C) without the suffix that determines whether the switch is usable in your rack, and "SN4600C, 64-port, 100G" describes both variants equally well.
What this does not change
Airflow direction has no effect on throughput, latency, port count, breakout behavior, routing features, or the operating system. Both part numbers carry Cumulus Linux and behave identically once installed correctly.
It also does not affect the operating-system question, which is encoded separately in the trailing C of the part number and is a different procurement issue entirely — see Cumulus Linux vs Onyx. A part number can be wrong on airflow, on operating system, or on both, and the two are independent.
For the full platform specification behind both variants, see the SN4600C datasheet.
Frequently asked questions
Can I change the airflow direction on an MSN4600 switch?
No. Airflow is fixed at manufacture. Fan modules and power supplies are keyed and marked by direction, and the chassis is built as either C2P or P2C. Reversing fans is not a supported conversion, and mounting the switch backwards puts the ports on the wrong face.
Which is C2P, the CS2RC or the CS2FC?
MSN4600-CS2RC is C2P — the R position in the part number marks connector-to-power, meaning air enters at the port side. MSN4600-CS2FC is P2C, with air entering at the power-supply side.
What happens if I install the wrong airflow variant?
The switch ingests hot exhaust instead of cold supply air, so it runs hot and drives its fans to maximum, and it vents its own exhaust into the cold aisle, raising intake temperature for everything else drawing from that face. It usually presents as a cooling problem elsewhere in the rack rather than as a fault on the switch.
Do CS2RC and CS2FC differ in performance?
No. Both are the same Spectrum-3 SN4600C platform with 64 QSFP28 ports at 100GbE, 6.4 Tb/s of switching capacity, and Cumulus Linux. Throughput, latency, features, and the operating system are identical.
How do I tell which variant a used switch is?
Read the ordering part number on the unit rather than trusting the listing. The R or F position identifies it, as does the NVIDIA SKU — 920-9N302-00R7-0C0 for C2P, 920-9N302-00F7-0C2 for P2C. A running switch will also report its platform and airflow from the operating system.
Related
NVIDIA SN4600C Specs & Datasheet (MSN4600-CS2RC)
The NVIDIA Spectrum-3 SN4600C is a 2U open Ethernet switch with 64 QSFP28 ports of 100GbE — 6.4 Tb/s of switching capacity and 8.4 Bpps of packet processing — built for spine and super-spine roles in large virtualized data centers and as the 100GbE storage and management fabric around GPU clusters. It ships under several MSN4600 ordering part numbers that differ only in airflow direction and preloaded network OS; MSN4600-CS2RC is the C2P, Cumulus Linux variant.
Read →Cumulus Linux vs Onyx: NVIDIA Switch Operating Systems
Cumulus Linux and Onyx are the two network operating systems NVIDIA has shipped preloaded on Spectrum Ethernet switches. Cumulus Linux is a Linux-native NOS managed with standard Linux tooling; Onyx (formerly MLNX-OS) is the older Mellanox-lineage switch OS. Current SN4600C ordering part numbers ship Cumulus Linux — marked by a trailing C in the part number — and the Onyx part numbers for that platform have been withdrawn.
Read →Last updated