hardMultiple Choice
XK0-006 Practice Question: During peak hours, a web server experiences…
During peak hours, a web server experiences timeouts. The kernel log shows 'possible SYN flooding'. Which kernel parameter should be increased to mitigate this?
⚠ Common exam trap
Test-takers frequently confuse the SYN backlog queue (`tcp_max_syn_backlog`) with the completed connection backlog (`somaxconn`), leading candidates to choose `net.core.somaxconn` even though it only affects fully established connections, not the SYN flood protection mechanism.
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
✓
net.ipv4.tcp_max_syn_backlog
The kernel log message 'possible SYN flooding' indicates that the system's SYN backlog queue is full, causing new connection requests to be dropped. Increasing `net.ipv4.tcp_max_syn_backlog` expands the maximum number of SYN requests that can be queued before the kernel starts dropping them, directly mitigating the issue.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
net.ipv4.tcp_syncookies
Why it's wrong here
tcp_syncookies is a boolean toggle, not a tunable value to increase; setting it to 1 enables SYN cookie protection, which statelessly validates handshakes under backlog pressure. It is the right defence when the SYN queue overflows. The stem asks which parameter to increase, pointing to backlog sizing rather than this on/off switch.
- ✗
net.core.somaxconn
Why it's wrong here
net.core.somaxconn caps the accept queue length, but the 'possible SYN flooding' message arises when the SYN backlog overflows before connections are accepted. Raising somaxconn alone leaves that backlog unchanged. The SYN backlog is sized by net.ipv4.tcp_max_syn_backlog, which is the parameter to increase here.
- ✓
net.ipv4.tcp_max_syn_backlog
Why this is correct
Raising `net.ipv4.tcp_max_syn_backlog` enlarges the queue holding half-open SYN_RECV connections awaiting the final ACK. Under peak load, that backlog overflows, so the kernel logs 'possible SYN flooding' and drops new handshakes. Increasing it lets the server absorb the burst, directly addressing the timeout constraint.
- ✗
net.core.rmem_default
Why it's wrong here
net.core.rmem_default sets the default socket receive buffer size, which governs how much inbound data a socket can hold, not how many half-open connection requests the backlog can absorb. It is tuned for throughput on high-bandwidth links. SYN flooding is mitigated by enlarging the accept queue or enabling syncookies.
Visual reference
Go deeper
Related to this question
About these practice questions
This XK0-006 question is part of Courseiva's 781-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This XK0-006 practice question is part of Courseiva's free CompTIA 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 XK0-006 exam.