OSFP<\/td> 8\u00d750G or 8\u00d7100G<\/td> No \u2014 different, larger cage<\/td> Depends on module and host platform<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\nThe CRS804-4DDQ uses QSFP56-DD ports designed for 400G operation over eight 50G PAM4 electrical lanes.<\/p>\n\n\n\n
QSFP112, by contrast, uses four electrical lanes operating at approximately 100G per lane. Although the naming and physical characteristics of different QSFP variants may appear similar, electrical lane mapping, firmware support, link modes, and module power requirements all determine actual compatibility.<\/p>\n\n\n\n
OSFP modules use a different and larger mechanical form factor and cannot be inserted directly into QSFP56-DD cages.<\/p>\n\n\n\n
Backward compatibility with earlier QSFP module generations also depends on the switch’s supported operating modes and module compatibility list. Mechanical compatibility alone does not guarantee successful link establishment.<\/p>\n\n\n\n
As a purchasing rule: choose optical transceivers and cables explicitly supported for the CRS804-4DDQ. A QSFP-DD label alone is not sufficient proof of compatibility.<\/strong><\/p>\n\n\n\n<\/span>Breakout: Turning Four Ports into Sixteen<\/strong><\/strong><\/span><\/h2>\n\n\n\nFour ports may seem limiting until you consider that each 400G port has eight independent 50G host-side electrical lanes.<\/p>\n\n\n\n
MikroTik supports configurable breakout modes, allowing the available 400G bandwidth to be divided into smaller Ethernet interfaces when the appropriate link modes and interconnects are used.<\/p>\n\n\n\nConfiguration<\/strong><\/strong><\/td>Ports Delivered<\/strong><\/strong><\/td>Typical Use<\/strong><\/strong><\/td><\/tr>4\u00d7400G<\/td> 4<\/td> GPU node interconnect, spine uplink<\/td><\/tr> 8\u00d7200G<\/td> 8<\/td> Compatible 200G NICs and uplinks<\/td><\/tr> 16\u00d7100G<\/td> 16<\/td> Existing 100G leaf switches, storage targets, 100G test equipment<\/td><\/tr> 400G \u2192 4\u00d7100G (compatible DR4 \u2192 4\u00d7DR1)<\/td> 16<\/td> Brownfield upgrades: retain 100G endpoints while introducing a 400G core<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\nThe 100G breakout path is particularly useful when upgrading existing data center networks.<\/p>\n\n\n\nA 400G DR4 transceiver uses four optical transmit lanes and four optical receive lanes, requiring eight fibers within an MPO-12 connector. Four 100G DR1 links likewise require four duplex fiber pairs, totaling eight fibers.<\/p>\n\n\n\n
With compatible optical modules, an MPO-12-to-4\u00d7LC breakout harness<\/strong> can connect one 400G DR4 interface to four independent 100G DR1 optical endpoints.<\/p>\n\n\n\nHowever, the harness itself only provides the physical fiber breakout. The switch must also be configured for 4\u00d7100G operation, and the optical modules, FEC settings, interface modes, and link partners must be compatible.<\/p>\n\n\n\n
This distinction matters: a physical breakout cable does not automatically create four operational Ethernet interfaces.<\/p>\n\n\n\n
With the correct configuration, the CRS804 can serve as a compact 400G aggregation platform while allowing existing 100G servers, storage devices, and network equipment to remain in service during the migration.<\/p>\n\n\n\n
Two practical cautions are worth emphasizing.<\/p>\n\n\n\n
First, the breakout harness must match the optical module’s fiber polarity and connector requirements, including MPO guide-pin configuration and APC polish where specified. An UPC-to-APC mismatch can cause excessive insertion loss, increased reflectance, or unreliable link operation.<\/p>\n\n\n\n
Second, each additional breakout connection introduces another potential point of failure. Document fiber polarity, port mapping, connector types, and link assignments before finalizing the cabling installation.<\/p>\n\n\n\n
<\/span>Management and RoCEv2<\/strong><\/strong><\/span><\/h2>\n\n\n\nManagement is standard MikroTik: RouterOS v7 provides configuration access through the CLI, WebFig browser interface, and WinBox desktop application.<\/p>\n\n\n\n
These familiar management options make the CRS804 approachable for network administrators already working with MikroTik equipment.<\/p>\n\n\n\n
For AI networking, one of the more important considerations is Priority Flow Control (PFC)<\/strong> and the broader set of congestion-management capabilities required by the intended workload.<\/p>\n\n\n\nThe switch provides configurable flow-control features, and RouterOS exposes the interface and breakout configuration directly.<\/p>\n\n\n\nIn independent testing, ServeTheHome reported using the CRS804 in an eight-node NVIDIA GB10 cluster running NCCL over an RDMA network.<\/p>\n\n\n\n
That result is encouraging for compact AI and GPU interconnect deployments, but successful RDMA operation should not be interpreted as a guarantee of lossless performance under every traffic condition.<\/p>\n\n\n\n
RoCEv2 deployments require careful validation of endpoint configuration, MTU, QoS mapping, PFC behavior, congestion-management features, and the specific RouterOS version.<\/p>\n\n\n\n
PFC alone does not guarantee a lossless Ethernet fabric. Incorrect configuration can cause congestion propagation, reduced throughput, or other performance problems.<\/p>\n\n\n\n
For teams without extensive RouterOS experience, AI-assisted tools can help interpret documentation, draft configuration commands, and simplify troubleshooting.<\/p>\n\n\n\n
However, changes involving port modes, flow control, QoS, and congestion management should still be reviewed and validated by a qualified network operator.<\/p>\n\n\n\n
AI assistance can lower the learning curve, but it does not replace engineering verification.<\/p>\n\n\n\n
<\/span>Measured Performance<\/strong><\/strong><\/span><\/h2>\n\n\n\nIndependent testing published by ServeTheHome reported the following aggregate throughput results.<\/p>\n\n\n\nTest<\/strong><\/strong><\/td>Result<\/strong><\/strong><\/td>Setup<\/strong><\/strong><\/td><\/tr>Keysight CyPerf<\/td> 1.567 Tbps<\/strong><\/td>4\u00d7DR4 to 4\u00d7DR4<\/td><\/tr> Keysight IxNetwork<\/td> 1.589 Tbps<\/strong><\/td>4\u00d7DR4 \u2192 16\u00d7DR1 (MPO-12-to-LC fanout)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\nSource: ServeTheHome, Cheap Desktop 400GbE Switch MikroTik CRS804-4DDQ-hRM Review<\/em>, September 3, 2026.<\/p>\n\n\n\nThese figures are independent third-party measurements, not FiberMall laboratory test results.<\/p>\n\n\n\n
The IxNetwork result is particularly interesting because the test achieved 1.589 Tbps of aggregate throughput using four 400G DR4 switch-side modules connected to sixteen 100G DR1 optical links.<\/p>\n\n\n\n
This corresponds to approximately 99% of the switch’s advertised 1.6 Tbps aggregate one-direction port bandwidth under the reported test conditions.<\/p>\n\n\n\n
The test demonstrates the potential of the CRS804’s 400G breakout capabilities. However, reproducing these results requires compatible traffic-generation equipment, transceivers, electrical PHY modes, FEC settings, and breakout configuration.<\/p>\n\n\n\n
Actual production performance also depends on packet sizes, traffic patterns, interface settings, and enabled switch features.<\/p>\n\n\n\n
For a chassis priced around $1,100, these third-party results indicate that the CRS804 can deliver impressive aggregate switching throughput for its price class.<\/p>\n\n\n\n<\/span>Power, Noise, and Rack Mounting<\/strong><\/strong><\/span><\/h2>\n\n\n\nServeTheHome reported an idle power draw of approximately 29.3 W<\/strong> in its test configuration.<\/p>\n\n\n\nMikroTik specifies a maximum rated power consumption of 123 W with attachments and 92 W without attachments. These figures represent maximum rated consumption under different configurations, not measured idle power.<\/p>\n\n\n\n
That distinction matters when comparing the CRS804 with larger data center switches.<\/p>\n\n\n\n
Depending on the model and configuration, used 32-port 100GbE switches can consume 900 W or more and generate noise levels exceeding 50 dBA.<\/p>\n\n\n\n
The CRS804’s lower power requirements make it attractive for smaller laboratories, edge installations, and compact high-speed network environments.<\/p>\n\n\n\n
Noise, however, remains an important consideration.<\/p>\n\n\n\n
Without optical modules installed, independent measurements place the CRS804 in the low-40 dBA range. Installing high-power 400G optics can increase fan speed and push the noise level above 50 dBA under certain operating conditions.<\/p>\n\n\n\n
This is acceptable in many equipment rooms and laboratory racks but less suitable for a quiet office or a desk directly beside the user.<\/p>\n\n\n\n
Rack mounting is flexible.<\/p>\n\n\n\n
A single unit can be installed in a standard 19-inch rack using the appropriate mounting accessories, while a dual-rack kit allows two units to occupy a single 1U space.<\/p>\n\n\n\n
One mechanical consideration is the distribution of weight toward the rear of the chassis, where the redundant power supplies are located.<\/p>\n\n\n\n
When installing the switch in a lightweight open-frame rack, ensure that the rack is stable, properly secured, and able to support the equipment safely. Additional shelf support may be appropriate.<\/p>\n\n\n\n
<\/span>The Optics Bill Nobody Budgets For<\/strong><\/strong><\/span><\/h2>\n\n\n\nHere is the arithmetic that actually determines the total cost of a 400G deployment.<\/p>\n\n\n\n
A 400G port is not simply a port on a switch. It is part of a complete interconnect system<\/strong> that includes the switch interface, optical transceiver or cable assembly, physical cabling, and the network adapter or equipment at the other end.<\/p>\n\n\n\nIn some deployments, the switching hardware may represent only a relatively small share of the overall link cost.<\/p>\n\n\n\n
The following table illustrates relative cost differences among common 400G interconnect options, using passive DAC as a baseline.<\/p>\n\n\n\n
These ratios are planning estimates rather than verified quotations. Actual pricing varies by vendor, reach, module specification, compatibility requirements, and order quantity.<\/p>\n\n\n\nOption<\/strong><\/strong><\/td>Reach<\/strong><\/strong><\/td>Typical Use<\/strong><\/strong><\/td>Relative Cost \/ Port<\/strong><\/strong><\/td><\/tr>400G QSFP-DD passive DAC<\/strong><\/td>1\u20133 m<\/td> Same-rack node-to-switch<\/td> 1\u00d7 baseline<\/td><\/tr> 400G QSFP-DD AOC<\/td> 3\u201330 m<\/td> Adjacent racks, short inter-rack links<\/td> 2\u20134\u00d7<\/td><\/tr> 400G DR4 (MPO-12, 8-fiber)<\/td> 500 m<\/td> Switch-to-switch, structured cabling<\/td> 8\u201320\u00d7<\/td><\/tr> 400G FR4 (duplex LC)<\/td> 2 km<\/td> Cross-building, campus<\/td> 15\u201330\u00d7<\/td><\/tr> 400G DR4 + 4\u00d7DR1 fanout<\/td> Up to 500 m, subject to link budget<\/td> 100G hosts connected to a 400G core<\/td> DR4 + harness + 4\u00d7DR1<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\nThe important lesson is that a relatively inexpensive 400G switch does not automatically mean an inexpensive 400G network.<\/p>\n\n\n\nA four-port CRS804 populated with DR4 transceivers and MPO fiber trunks can require a substantially larger total investment than the chassis price alone suggests.<\/p>\n\n\n\n
If the connected devices are located within the same rack, compatible passive DAC cables are often the most economical interconnect option.<\/p>\n\n\n\n
They eliminate the need for separate optical transceivers and fiber patch cables while providing short-reach, high-bandwidth connectivity with minimal additional latency.<\/p>\n\n\n\n
This is one of the deployment scenarios in which the CRS804’s price advantage becomes particularly attractive.<\/p>\n\n\n\n
<\/span>Three Ordering Notes That Prevent Returns<\/strong><\/strong><\/span><\/h3>\n\n\n\n1. Match the host cage, not just the speed.<\/strong><\/p>\n\n\n\nA 400G-capable host may use QSFP-DD or OSFP interfaces depending on its network adapter and hardware generation.<\/p>\n\n\n\n
For example, certain high-speed NVIDIA ConnectX platforms use OSFP interfaces, while the CRS804-4DDQ uses QSFP56-DD.<\/p>\n\n\n\n
Connecting these devices requires a cable assembly or optical transceiver solution compatible with both endpoints, including their electrical lane configurations, supported link speeds, FEC requirements, and physical connectors.<\/p>\n\n\n\n
Do not assume that a passive form-factor adapter automatically resolves differences in electrical signaling or supported operating modes.<\/p>\n\n\n\n
Before ordering, verify the complete host-to-switch interconnect configuration.<\/p>\n\n\n\n
2. DR4 is not DR4 everywhere.<\/strong><\/p>\n\n\n\nAlthough 400G DR4 defines a standardized optical interface, actual module implementations and deployment requirements must still be checked.<\/p>\n\n\n\n
Confirm the number of active fibers, MPO connector type, polarity method, connector polish, supported breakout modes, and host compatibility.<\/p>\n\n\n\n
A typical 400G DR4 interface uses eight active fibers within an MPO-12 connector, but the complete cable assembly must match the optical equipment.<\/p>\n\n\n\n
3. Do not automatically buy 400G optics for a single 100G connection.<\/strong><\/p>\n\n\n\nIf the endpoint uses a 100G interface, a compatible QSFP28 transceiver operating in a supported 100G mode may provide a simpler solution than a 400G DR4 breakout configuration.<\/p>\n\n\n\n
However, backward compatibility must be verified against MikroTik’s supported module list and the required port configuration.<\/p>\n\n\n\n
Installing a single QSFP28 module in a compatible QSFP-DD cage does not create four independent physical QSFP28 sockets.<\/p>\n\n\n\n
When four separate 100G DR1 endpoints must be connected through one 400G port, a supported 400G DR4 module with an appropriate MPO-to-LC breakout harness remains a practical option.<\/p>\n\n\n\n