---
title: "10G to 25G Migration: When the Per-Port Economics Justify the Switch"
slug: "25g-vs-10g-upgrade-path-sfp28-sfp-plus"
type: analysis
category: "Migration & Upgrades"
tags: ["25G", "10G", "SFP28", "SFP+", "migration", "TOR switch", "server connectivity", "enterprise"]
seo_focus_keyword: "10G to 25G migration SFP28 upgrade decision"
---

The move from 10G to 25G server connectivity has been underway for long enough that the decision tree is reasonably well-established, but the number of enterprises still running 10G ToR infrastructure in new deployments suggests the economic case isn't as clear as the bandwidth case. The honest answer is: 25G is almost always the right choice for new deployments, and the reasons why many organizations still choose 10G have more to do with procurement inertia and cabling assumptions than actual economics.

## The Per-Port Cost Comparison in 2024

The hardware economics have shifted significantly over the past five years. In 2019, 10G SFP+ SR optics were approximately 30% cheaper than 25G SFP28 SR equivalents, and 10G ToR switches were substantially cheaper than 25G switches in 48-port configurations. By 2024, the economics look different:

A 25G SFP28 SR optic from a quality third-party manufacturer runs €25–€45 depending on volume. A 10G SFP+ SR optic from the same manufacturer runs €15–€25. The per-port cost delta is €10–€20, or roughly 40–60% more for 25G. That's a real premium.

The switch-level comparison is more nuanced. A 48-port 25G ToR switch (e.g., Arista 7050CX3-48YC12, Cisco Nexus 93180YC-FX) runs approximately €8,000–€15,000 at current street prices depending on vendor and optic count. A comparable 48-port 10G ToR switch runs €4,000–€8,000. The 25G switch premium is roughly €5,000–€7,000 per switch, or approximately €100–€150 per port—versus the €10–€20 per-port optic cost delta.

The capital cost comparison thus comes out to roughly €120–€170 per port more expensive for 25G versus 10G in a fresh deployment. Over a 5-year hardware lifecycle, this is approximately €25–€35 per port per year.

## The Bandwidth Economics and Lifecycle Consideration

A 25G port delivers 2.5× the bandwidth of a 10G port at roughly 1.5–1.7× the cost. The cost-per-Gbps comparison favors 25G: approximately €5–€7 per Gbps for 25G versus €8–€12 per Gbps for 10G at current prices.

The lifecycle argument is stronger than the initial cost argument. Infrastructure installed today will remain in service for 5–7 years under typical enterprise refresh cycles. The server connectivity requirements at the end of that cycle—2029 or 2030—will reflect application workloads that are being planned and deployed now. AI/ML inference workloads, high-frequency data analytics, containerized microservices with high east-west traffic volumes, NVMe-over-Fabric storage—all of these drive higher bandwidth utilization per server than a 10G link was designed to sustain under the workloads of 2015.

Installing 10G in a new deployment in 2024 means accepting mid-cycle obsolescence around 2027–2028 when server bandwidth requirements start to exceed 10G sustained utilization rates, requiring either a refresh ahead of the planned cycle or bandwidth-constrained application performance.

## SFP28 vs. SFP+ Physical Compatibility

SFP28 and SFP+ use the same SFF-8402 mechanical form factor. An SFP28 module will physically fit in an SFP+ port, and vice versa. However, the electrical interface specifications differ:

SFP+ operates at the 10GBASE-SR/LR Ethernet or 10G Fibre Channel electrical interface rate. SFP28 operates at 25GBASE-SR/LR electrical interface rate. The host port's SerDes (Serializer/Deserializer) determines which speeds are supported.

In practice: an SFP28 module inserted into an SFP+ port will typically auto-negotiate to 10G operation or fail to link, depending on the platform. It will not run at 25G in an SFP+ port regardless of the module's specifications. Conversely, an SFP+ module in an SFP28 port will typically run at 10G if the switch supports 10G on that port interface type.

This backward compatibility is useful for mixed-generation migrations. A 25G ToR switch with 48 SFP28 ports can accept SFP+ 10G modules in ports that connect to servers not yet upgraded to 25G NICs—a common scenario during a phased server refresh where ToR switches are upgraded before all servers. The SFP28 port runs at 10G with the SFP+ module without any configuration change in most implementations.

## TOR Cabling Scenarios: What Changes and What Doesn't

The fiber plant between ToR switches and servers doesn't change at all for SR applications. 25GBASE-SR uses 850 nm VCSEL over OM3/OM4 on LC duplex—the same fiber and connector type as 10GBASE-SR. A server rack with OM4 patch cords pre-installed for 10G can have its transceivers swapped to 25G without touching the fiber. This is a material point for existing data centers: the cabling investment is preserved.

The cabling considerations that do change are at the ToR-to-ToR level. If you're also upgrading uplinks from 10G to higher speed, the uplink ports on 25G ToR switches are typically 100G QSFP28 (4×25G) rather than 40G QSFP+. This changes the cable type for uplinks, but the switch-to-leaf fiber runs are typically shorter-reach and are being installed fresh in most refresh projects anyway.

For direct attach copper (DAC) connections—common in top-of-rack server to switch connections up to 3–5 meters—the change from 10G to 25G means new DAC cables. SFP28 25G DAC cables are not compatible with SFP+ 25G ports because the electrical signaling is different, and while the connectors are mechanically interchangeable, the active copper or passive twinax cable must be rated for the appropriate speed. Existing 10G DAC cables need replacement in a 25G migration.

## Why Most Enterprises Do This Wrong

The typical suboptimal migration pattern is: an organization approves a server refresh, new servers arrive with dual 25G NICs, and procurement orders 10G ToR switches "because we have 10G SFP+ switches from the last cycle and we want to standardize." This decision optimizes for the wrong variable—minimizing OpEx on network hardware in the short term at the cost of deploying infrastructure that is obsolete by design.

The second common mistake is upgrading ToR switches to 25G while keeping 10G uplinks, creating a 25G-to-10G speed mismatch at the aggregation layer that immediately limits the achievable bandwidth per ToR switch to the uplink capacity rather than the server-facing capacity. If you're migrating to 25G at the server layer, the aggregation layer uplinks need to be part of the same migration plan.

The correct migration sequence is: upgrade ToR switches and uplinks first (25G ports, 100G uplinks), then migrate servers as they're refreshed. This allows existing 10G servers to run at 10G on the new infrastructure (using SFP+ backward compatibility) while new 25G servers get full-speed connectivity immediately. The infrastructure investment is complete at the start, and no second migration is required when the last 10G server is replaced.

The economics justify 25G for essentially any enterprise deploying more than 100 server ports in a new facility or major refresh today. The argument for 10G boils down to "we're at end of lease and this will be torn down in 18 months"—which is a legitimate exception, not a default.
