DIRECT ANSWER / 01
Confirm equipment and mating parts before freezing cable configuration
400G does not identify a single optical interface. Cisco’s current official module material, for example, includes DR4 on parallel singlemode MPO-12, FR4 on duplex-LC singlemode WDM, and SR8 on multimode MPO-16. Choose cabling from the complete module references and the platform compatibility matrix.
“400G MPO” is not a purchasing specification. First distinguish parallel optics from WDM, SMF from MMF, and direct links from breakouts. Then define end face, gender, polarity, length and testing.
SELECTION MATRIX / 02
Purchasing decision matrix
| Item | Identify | Correct action | Avoid |
|---|---|---|---|
| 400GBASE-DR4 | Parallel SMF on MPO-12 | Parallel singlemode equipment links; some modules support 4×100G breakout | Verify module reference, APC, fibre count, gender, map and remote end |
| 400GBASE-FR4 | Duplex-LC SMF with in-module WDM | Links using duplex-fibre infrastructure | Verify LC UPC, modules at both ends, wavelength architecture and reach |
| 400GBASE-SR8 | Parallel MMF on MPO-16 | Short-reach parallel multimode links | Verify MPO-16 APC, OM grade, adapter and breakout target |
RFQ INPUTS / 03
Minimum inputs a supplier can verify
| Category | Required input or confirmation |
|---|---|
| Equipment and modules | Switch/NIC plus full module references, software and compatibility matrix |
| Optical interface | DR4 / FR4 / SR8; MPO-12 / MPO-16 / LC; APC or UPC |
| Link architecture | Direct or breakout, lane map, installed trunks and intermediate connections |
| Delivery | Length datum, labels, quantity, test method and report format |
BUYER FAQ / 04
Purchasing FAQ
Does every 400G link use MPO?
No. Official 400G portfolios include MPO-12, MPO-16 and duplex LC. The exact module determines the interface.
Can DR4 and FR4 use the same patch cable?
No selection can be made from rate alone. DR4 uses parallel MPO-12 while FR4 uses duplex LC; both mechanics and optical architecture differ.
Can SR8 be sourced as ordinary MPO-12?
No. MPO-16 interface, key orientation and mating parts must be checked against the complete reference.
How can an RFQ avoid a mismatch?
Send both module references, port photos, direct/breakout objective and lane map for review.
SOURCES / 05
Sources and applicability
Sources checked: 2026-09-22. This guide clarifies purchasing fields; it does not replace current equipment data sheets, full standards or the approved project drawing.