Buffer Credit Loss Recovery Methods
Which TWO of the following are valid methods to recover from buffer credit loss on a Fibre Channel link?
Quick Answer
The correct answer is that increasing the BB_Credit value is one valid method, while reducing the link speed is the other. Reducing the link speed recovers from buffer credit loss by lowering the frame transmission rate, which gives the receiver’s buffer credits time to replenish and prevents overrun, effectively stabilizing the link during credit starvation caused by long distances or congestion. On the Cisco DCCOR 350-601 exam, this concept tests your understanding of Fibre Channel flow control and buffer-to-buffer credits, often appearing in a “choose two” format where a common trap is selecting “increase the link speed” instead of decreasing it. Remember that slowing down the link is a temporary workaround that sacrifices bandwidth for stability. A helpful memory tip: “Slow the flow to let credits grow.”
⚠ Common exam trap
Cisco often tests the misconception that increasing link speed or aggregating links (port channels) can solve buffer credit issues, but the correct approach is to either reduce speed or increase BB_Credits, as credit loss is a flow-control problem, not a bandwidth problem.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Reduce the link speed.
Reducing the link speed is a valid method to recover from buffer credit loss because it decreases the number of frames transmitted per unit time, allowing the receiver's buffer credits to replenish and preventing further overrun. This is a temporary workaround that reduces the effective bandwidth but can stabilize the link when buffer credit starvation occurs due to distance or congestion.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Reduce the link speed.
Why this is correct
Lower speed reduces the number of credits needed to maintain the link.
- ✓
Increase the BB_Credit value.
Why this is correct
Configuring more buffer credits compensates for credit loss.
- ✗
Enable WRED on the switch.
Why it's wrong here
WRED is for congestion avoidance in IP networks, not Fibre Channel.
- ✗
Use port channel to aggregate links.
Why it's wrong here
Port channels increase bandwidth but do not address buffer credit depletion.
- ✗
Credit recovery using RDMA.
Why it's wrong here
RDMA is used in Ethernet networks, not for Fibre Channel buffer credits.
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Same concept, more angles
1 more way this is tested on 350-601
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A storage network engineer notices high buffer credit starvation counters on an inter-switch link. What is the most effective solution to reduce this issue?
medium- A.Change the ISL port mode from E to F.
- B.Reduce the ISL speed to 1 Gbps.
- ✓ C.Increase the number of buffer credits on the ISL.
- D.Enable QoS to prioritize buffer credit recovery.
Why C: High buffer credit starvation counters on an inter-switch link (ISL) indicate that the switch is running out of buffer credits to send frames, causing pauses in transmission. Increasing the number of buffer credits on the ISL directly addresses this by providing more credit pool for the link, allowing the switch to send more frames before needing acknowledgment, thus reducing starvation and improving throughput.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-601 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-601 exam.