Quick Answer
The correct answer is that Fibre Channel buffer credits control the flow of frames between directly connected ports. This credit-based flow control mechanism, known as BB_Credit, ensures lossless transmission by requiring each port to advertise its available receive buffers to its directly attached peer; the sender may only transmit a frame when it holds a positive credit count, preventing buffer overflow and frame drops at the receiver. On the Cisco DCCOR and CCNP Data Center Core 350-601 exam, this concept tests your understanding of Fibre Channel’s unique lossless behavior versus Ethernet’s pause-based flow control—a common trap is confusing buffer credits with end-to-end credit or assuming they apply across switches rather than only on the direct link. Remember the memory tip: “Buffer credits are for the buddy on the wire, not the whole network.”
This 350-601 practice question tests your understanding of storage network. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which statement about Fibre Channel buffer credits is true?
They are used for load balancing across multiple paths.
Why wrong: Load balancing is done by other mechanisms.
They control the flow of frames between directly connected ports.
Buffer credits manage the number of outstanding frames.
They are allocated per VSAN.
Why wrong: Buffer credits are allocated per port.
They detect CRC errors in frames.
Why wrong: CRC is for error detection, not buffer credits.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
They control the flow of frames between directly connected ports.
Fibre Channel buffer credits implement a credit-based flow control mechanism between directly connected ports (Nx_Port to Fx_Port or E_Port to E_Port). Each port advertises its available buffer credits (BB_Credit) to the directly attached peer, and the sender can only transmit a frame when it has a positive credit count. This prevents frame loss due to buffer overflow at the receiver, ensuring lossless transmission over the link.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
They are used for load balancing across multiple paths.
Why it's wrong here
Load balancing is done by other mechanisms.
They control the flow of frames between directly connected ports.
Why this is correct
Buffer credits manage the number of outstanding frames.
Related concept
Read the scenario before looking for a memorised answer.
They are allocated per VSAN.
Why it's wrong here
Buffer credits are allocated per port.
They detect CRC errors in frames.
Why it's wrong here
CRC is for error detection, not buffer credits.
Common exam traps
Cisco often tests the distinction between flow control (buffer credits) and error detection (CRC) or fabric-level features (VSANs, load balancing), so the trap here is confusing a link-level mechanism with higher-layer or fabric-wide functions.
Detailed technical explanation
Buffer credits are negotiated during the Exchange Link Parameters (ELP) process when a link comes up, and each port advertises its BB_Credit value (typically 0–255 for standard links, up to 4095 for extended links). In long-distance Fibre Channel links (e.g., over dark fiber or DWDM), insufficient buffer credits can cause performance degradation because the round-trip time exceeds the credit window; engineers must calculate the required BB_Credit using the formula: BB_Credit = (Distance in km × 2 × 1000) / (Frame Size in bytes / 2) to maintain full throughput.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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FAQ
Storage Network — This question tests Storage Network — Read the scenario before looking for a memorised answer..
The correct answer is: They control the flow of frames between directly connected ports. — Fibre Channel buffer credits implement a credit-based flow control mechanism between directly connected ports (Nx_Port to Fx_Port or E_Port to E_Port). Each port advertises its available buffer credits (BB_Credit) to the directly attached peer, and the sender can only transmit a frame when it has a positive credit count. This prevents frame loss due to buffer overflow at the receiver, ensuring lossless transmission over the link.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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