N10-009 Question 101
Single answerForm factors: Small form-factor pluggable (SFP), Quad small form-factor pluggable (QSFP)A network administrator is upgrading the uplinks between a top-of-rack switch and the data center core. The new core switch has QSFP+ ports available, while the existing top-of-rack switch has SFP+ 10 GbE uplink ports. The administrator needs to provide four separate 10 GbE connections from a single port on the core switch to the top-of-rack switch, using supported modular interfaces rather than replacing either switch. Which solution should the administrator choose?
- A
Install a QSFP+ to 4x SFP+ breakout cable on the core switch and connect the four 10 GbE lanes to the SFP+ ports on the top-of-rack switch
- B
Install a standard SFP transceiver in the QSFP+ port on the core switch and connect it directly to one SFP+ port on the top-of-rack switch
- C
Use a QSFP28 transceiver in the core switch port because QSFP28 is backward compatible with all SFP+ interfaces
- D
Use an RJ45 copper transceiver in the QSFP+ port and split it into four Ethernet patch cables to the top-of-rack switch
Show answer and explanation
Correct answer: A
Explanation
The best solution is to use a QSFP+ to 4x SFP+ breakout cable, assuming both the core switch and its operating system support breakout mode on that port. In practical deployments, QSFP+ commonly supports 40 GbE, which can be divided into four 10 GbE lanes for connectivity to SFP+ interfaces. This is a standard use case in data centers where higher-density aggregation switches connect to access or top-of-rack switches with 10 GbE uplinks. By contrast, SFP and QSFP are different physical form factors and are not directly interchangeable. Network+ candidates should recognize both the physical differences and the operational use case: SFP/SFP+ is typically used for single-lane links, while QSFP/QSFP+ supports multi-lane higher-bandwidth connectivity and, on supported platforms, breakout into multiple lower-speed links. Vendor documentation from major switch manufacturers such as Cisco, Juniper, and Arista commonly notes that breakout support is platform- and port-specific, so verifying compatibility is a best practice before deployment.
- A. Correct.
Correct. A QSFP+ port can be used for breakout in many supported switch platforms, allowing one 40 GbE QSFP+ interface to split into four independent 10 GbE links. This is a common data center design when a higher-density core switch must connect to multiple SFP+ interfaces on another switch. The key is that the switch hardware and software must support breakout mode, and the correct breakout cable or optics must be used.
- B. Incorrect.
Incorrect. A standard SFP transceiver does not fit into a QSFP+ port because the form factors are physically different. Even though both are pluggable optics, QSFP+ and SFP/SFP+ are not interchangeable modules. This option reflects a common misconception that any pluggable optic can be inserted into any modular port.
- C. Incorrect.
Incorrect. QSFP28 is a 100 GbE form factor and is not universally backward compatible with SFP+ interfaces. A QSFP28 module also does not solve the requirement to present four separate 10 GbE links to SFP+ ports unless the specific hardware supports an appropriate breakout configuration. Assuming all newer form factors are automatically compatible with older ones is a common error.
- D. Incorrect.
Incorrect. QSFP+ ports are not designed to be converted into four separate RJ45 Ethernet patch cable connections with a simple split. Ethernet links require supported transceivers, signaling standards, and switch support. Passive cable splitting of one switched uplink into multiple independent RJ45 links is not how modular Ethernet uplinks work.