FIELD GUIDESource-led reference
Port & Cable

P810 / Network / Cable / adapter

Cisco QSFP-4SFP10G-CU3M — four-port breakout DAC

Connect a supported 40G QSFP port configured for breakout to four supported 10G SFP+ ports.

Also called Cisco QSFP-4SFP10G-CU3M, 3m passive breakout

A breakout cable is not an Ethernet switch, a splitter that duplicates traffic, or a QSFP-to-single-SFP adapter.

The useful distinction

Match the complete manufacturer identity, endpoint roles and selected length; a similar shell or cable color is insufficient.

Claim inspection dates: 2026-10-23 · Independent review pending

Cable / adapter note · not an individual product specification

The useful distinction

Understand the requirement.

Connect a supported 40G QSFP port configured for breakout to four supported 10G SFP+ ports. [C990A]

Bounded facts, visible unknowns

Specifications and limits

Cisco QSFP-4SFP10G-CU3M — four-port breakout DAC facts and limitations
Documented task / modeQSFP-to-four-SFP+ copper breakout; host port must support the required breakout mode and lane mapping. [C990A]
Construction / lengthPassive copper breakout assembly; exact table lists 30AWG and PVC for this PID. 3m PID; Table7 separately locates the fan-out 1m from the QSFP end. That 1m figure is not total cable length. [C990A]
Verified device listNot included. Check exact device and accessory documentation.
A boundary, not an omission to guess around.

Passive copper breakout assembly; exact table lists 30AWG and PVC for this PID. Allow separate clearance and bend space for the QSFP trunk and SFP+ branches; do not load neighboring ports with the breakout body.

Before you connect

What to check

  1. Read the exact platform's breakout-port and software table; record subport lane mapping before requesting a configuration change.
  2. Check condition with power disconnected where the equipment guidance permits; stop for damage, heat or unknown powered connections.
  3. Keep published source support separate from physical test results.
Trace a supported connection class →

Direction and fallback

Four two-way 10G branches fan out from a documented QSFP breakout-capable port; this is not four copies of a single received packet stream. Automatic conversion into four links from an arbitrary QSFP port is not established; software, port grouping and supported rates matter.

Worked selection example

Where the switch manual explicitly supports four 10G subports on the chosen QSFP port, map each labelled branch to its intended SFP+ peer and retain that map in the support record.

What to observe next

Read the exact platform's breakout-port and software table; record subport lane mapping before requesting a configuration change.

Your next step

Move from the form to the requirement.

Compare this field note See the differences without assuming interchangeability.Work through a connection Choose your task before deciding on a cable.Explore this evidence trail Inspect the claims and their dependencies.

The source trail

Evidence for this page

AI-assisted inspection is not independent engineering review. Source scope and access limitations are disclosed below. Procedural checklists are editorial requirements, not hardware measurements.

C990ASource checked · pending review

QSFP-to-four-SFP+ copper breakout; host port must support the required breakout mode and lane mapping. No PoE or endpoint charging. Exact assembly consumption is not established by the inspected cable-dimension table. Passive copper breakout assembly; exact table lists 30AWG and PVC for this PID. 3m PID; Table7 separately locates the fan-out 1m from the QSFP end. That 1m figure is not total cable length.

Cisco · Cisco 40GBASE QSFP Modules Data Sheet ↗

Locator: QSFP-to-Four-SFP+ copper breakout section; Table 1; Table 7 breakout location; Table 8 dimensions
Access: public page. Exact QSFP-4SFP10G-CU3M breakout role. Table 7's 1m is breakout location from QSFP, not cable length.

S1108: full source recordInspect review dependencies →

Claim scope: Cisco QSFP-4SFP10G-CU3M, 3m passive breakout. Next review due 2027-01-21.

Suggest a correction to this field note →

Evidence behind this page

Scope first. Source second. Approval separate.

1 linked sources · 1 scoped claims · 0 sources with inspection/access flags.

Page scope: content_program_cable_selection

Assessment 2026-10-23 · earliest scheduled source review 2027-01-21. This is a recorded-date assessment, not a live source check. Page-level independent review is not established by this panel.

Inspect 1 source scopes, access limits and dates

S1108 · Cisco 40GBASE QSFP Modules Data Sheet

Cisco · Manufacturer / product-owner domain · inspected 2026-10-23 · due 2027-01-21

Within inspection window

Scoped support: Exact QSFP-4SFP10G-CU3M breakout role. Table 7's 1m is breakout location from QSFP, not cable length.

Not established / limitations: Exact QSFP-4SFP10G-CU3M breakout role. Table 7's 1m is breakout location from QSFP, not cable length.

Locator: QSFP-to-Four-SFP+ copper breakout section; Table 1; Table 7 breakout location; Table 8 dimensions

Trace 1 claims to their source records

C990A · P810

QSFP-to-four-SFP+ copper breakout; host port must support the required breakout mode and lane mapping. No PoE or endpoint charging. Exact assembly consumption is not established by the inspected cable-dimension table. Passive copper breakout assembly; exact table lists 30AWG and PVC for this PID. 3m PID; Table7 separately locates the fan-out 1m from the QSFP end. That 1m figure is not total cable length.

Claim scope: Cisco QSFP-4SFP10G-CU3M, 3m passive breakout

Source links: S1108 · Evidence trail →

Prepare this page for review →Read the evidence method →

Recorded evidence only. An inspection date, publisher label, source link or generated packet is not independent technical review, hardware testing, fabrication approval or a compatibility verdict.