How to Choose the Right 400Gb Switch for Your Data Center

The right 400Gb switch is the one that fits its role in your fabric. Decide whether it is a spine, an AI back-end leaf, a deep-buffer edge or a migration step from 100G, then match port count, buffer architecture, optics form factor and network operating system to that role. Price comes last, because at 400G the switch itself may not be the biggest line on the bill once optics, licensing and support are added. This guide compares the 400G switches Nexus Compute supplies from Arista, Cisco and NVIDIA, and answers the pricing question buyers ask most about Arista.

What role will the 400G switch play in your fabric?

• General-purpose 400G spine: fixed 32-port 1U boxes such as the Arista 7060DX4-32, the Cisco Nexus 9332D-GX2B and the NVIDIA SN4700, all 32 x 400GbE QSFP-DD. At 64 ports in 2RU, the Cisco Nexus 9364D-GX2A doubles the radix.
• AI and GPU back-end fabric: high radix, RoCEv2 and low latency. The NVIDIA SN5600 puts 128 x 400GbE (64 OSFP cages, split) in 2U with adaptive routing, and the Arista 7060DX5-64S offers 64 x 400GbE with a 114 MB shared buffer and RoCEv2 congestion management.
• Deep-buffer spine, edge and DCI: the Arista 7280DR3-24 pairs 24 x 400GbE with a VOQ architecture on Jericho2-class silicon and a multi-GB dynamic buffer.
• Migration from 100G: mixed-speed switches such as the Cisco Nexus 93600CD-GX (28 x 100G QSFP28 plus 8 x 400G QSFP-DD) and the Arista 7280CR3-32P4 (32 x 100GbE plus 4 x 400GbE) keep 100G downlinks and add 400G uplinks.
• Large AI spine: the Arista 7808R4 is an 8-slot modular chassis with 36 x 800GbE per line card and breakout to 400G, for fabrics that outgrow fixed switches.

How many ports and how much breakout do you need?

In a two-tier leaf-spine design, the spine's port count caps how many leaves the fabric can hold, so a 64-port spine supports twice as many leaves as a 32-port one before you add a third tier. Breakout stretches that further when leaves or servers run at 100G. The Nexus 9332D-GX2B breaks out to as many as 128 x 100G or 64 x 200G, the 7060DX5-64S to 256 x 100G, and the Nexus 9364D-GX2A supports 4 x 10/25/50/100G or 2 x 200G per port. Count the ports you need in year three, not on day one. One caution when comparing spec sheets: vendors quote capacity differently. Some count one direction, some count both. A 32 x 400G switch moves 12.8 Tbps in each direction, which is 25.6 Tbps counted full-duplex. That is why the Nexus 9332D-GX2B is listed at 12.8 Tbps and the Arista 7060DX4-32 at 25.6 Tbps despite the same port count. Compare port count multiplied by port speed, then look at buffer, latency and features.

Shallow buffer or deep buffer?

Deep-buffer switches built on VOQ architectures, such as the 7280DR3-24 and the Jericho3-AI based 7808R4, absorb incast bursts and speed mismatches that would overflow a smaller buffer. That suits spines facing storage, WAN edges and data center interconnect. High-radix switches with shared on-chip buffers (64 MB on the SN4700, 114 MB on the 7060DX5-64S) win on port density per rack unit and on latency, and they rely on ECN and PFC to manage congestion in AI and leaf roles. If you are unsure which your traffic needs, our guide to congestion control in AI training fabrics explains the mechanisms.

Does it matter whether the switch uses QSFP-DD or OSFP?

Yes, because the optics must match the cage. The Arista and Cisco 400G switches here use QSFP-DD, while the NVIDIA SN5600 and the Quantum-2 InfiniBand switches use OSFP. QSFP-DD cages also accept QSFP28 modules, which makes gradual migration from 100G simpler. Mixing QSFP-DD and OSFP platforms means stocking two families of transceivers and cables. See 100G vs 400G transceivers explained before you size the optics order.

Do you need 400G Ethernet or 400G InfiniBand?

The NVIDIA Quantum-2 QM9700 and QM9790 are NDR InfiniBand switches, not Ethernet: 64 x 400Gb/s through 32 OSFP cages with SHARPv3 in-network computing. The QM9700 is managed with an embedded subnet manager, and the QM9790 is externally managed through NVIDIA UFM. Choose InfiniBand for a dedicated GPU training fabric, and 400G Ethernet with RoCEv2 when the same network must also carry storage and general data center traffic.

Which network operating system fits your team?

Operating system is where much of the long-term cost sits. Arista switches run EOS with CloudVision. The Cisco Nexus 9332D-GX2B and 9364D-GX2A run in NX-OS or ACI spine mode, and the 93600CD-GX in NX-OS or ACI. NVIDIA Spectrum switches run open operating systems, Cumulus Linux or SONiC. A switch your engineers already know how to automate, monitor and upgrade is usually cheaper to run than a slightly cheaper switch they do not.

How does the pricing of Arista switches compare to other brands?

There is no honest one-line answer, because list prices and project prices differ widely, and a fair comparison has to be like for like: the same silicon class, the same port count and the same support term. What moves the total is consistent across Arista, Cisco and NVIDIA:

• Silicon and buffer class: deep-buffer VOQ platforms such as the 7280R3 and 7800R4 generally carry a premium over high-radix shared-buffer switches with the same number of ports.
• Port count, speed and form factor: a 64-port 2U switch generally costs more than a 32-port 1U one, and a modular chassis adds supervisors, fabric modules and line cards.
• Optics: at 400G, populating every port with transceivers can rival or exceed the cost of the switch, so price optics and cables in the same quote.
• Software licensing: Arista CloudVision is licensed separately from the switch, Cisco sells Nexus software in licensing tiers with ACI also needing APIC controllers, and NVIDIA UFM is a separate software product for managing InfiniBand fabrics.
• Support: Cisco Smart Net, Arista and NVIDIA support contracts, each priced by term and response level.

Compare 400G switches on three- to five-year cost per usable port, including optics, licenses and support. Hardware price alone ranks them wrongly more often than not.

Current pricing appears on each product page or is quoted on request. Nexus Compute can quote an Arista option and a Cisco or NVIDIA option side by side with optics and support included, so the comparison runs on your port count rather than a list price. Shortlist by role first, then ask for both brands in the same quote.

400G switch buying checklist

• Role in the fabric, and the number of leaves or servers it must connect in year three.
• Ethernet with RoCEv2, or InfiniBand for a dedicated training fabric.
• Buffer architecture: deep-buffer VOQ or high-radix shared buffer.
• Optics cage (QSFP-DD or OSFP), breakout requirements and cable reach.
• Network OS, management platform and any controller or license it depends on.
• Airflow direction to match your hot and cold aisles, and redundant power.
• Support term and response level, aligned with the rest of the network.