FIELD GUIDESource-led reference
Port & Cable

Network · Exact Product Example

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

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

One QSFP end at breakout-capable portend A
Four integral SFP+ branchesend B
Bidirectionaldirection evidence
Passiveconversion

Endpoint map

Start with what is physically represented

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.

One QSFP end at breakout-capable port reference →Four integral SFP+ branches reference →Compare references with these ends →Canonical cable/adapter note →

Choose for the actual job

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

ConstructionDocumented

Passive copper breakout assembly; exact table lists 30AWG and PVC for this PID.

Evidence: C990A

Fallback / lower modesConditional

Automatic conversion into four links from an arbitrary QSFP port is not established; software, port grouping and supported rates matter.

Evidence: C990A

Environment and handlingConditional

Allow separate clearance and bend space for the QSFP trunk and SFP+ branches; do not load neighboring ports with the breakout body.

Evidence: C990A

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.

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

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

Source-documented example; no hardware test

Capability ledger

Six questions kept separate

DataDocumented

QSFP-to-four-SFP+ copper breakout; host port must support the required breakout mode and lane mapping.

Evidence: C990A

Power / chargingConditional

No PoE or endpoint charging. Exact assembly consumption is not established by the inspected cable-dimension table.

Evidence: C990A

VideoNot Applicable

No native display mode represented.

ConversionPassive

Passive copper breakout assembly; exact table lists 30AWG and PVC for this PID.

Evidence: C990A

Length / reachDocumented

3m PID; Table7 separately locates the fan-out 1m from the QSFP end. That 1m figure is not total cable length.

Evidence: C990A

Markings / certificationConditional

Record the complete PID and branch/lane identifiers; QSFP and SFP+ shapes alone do not establish breakout support.

Evidence: C990A

Explicit unknowns
  • No physical sample, electrical/optical measurement or hardware interoperability test was performed.
  • Read the exact platform's breakout-port and software table; record subport lane mapping before requesting a configuration change.

Source boundary

Why this profile says what it says

Back to first citation ↑

Source records: S1108

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.

Scope: Cisco QSFP-4SFP10G-CU3M, 3m passive breakout · review due 2027-01-21

Cisco · Cisco 40GBASE QSFP Modules Data Sheet

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

Open source ↗

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

Evidence behind this page

Scope first. Source second. Approval separate.

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

Page scope: exact-product-example

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.