SSCP Network and Communications Security Practice Question
Which TWO of the following are methods to defend against SYN flood attacks? (Select TWO)
⚠ Common exam trap
Watch out — candidates often confuse general TCP hardening features (timestamps, routing) with actual SYN flood mitigations — candidates often pick 'increase backlog' as the only answer and miss SYN cookies, or select UDP as a workaround without realizing it breaks the protocol.
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
✓
Increasing the SYN backlog queue size
Option C (Increasing the SYN backlog queue size) is correct because a SYN flood exhausts the backlog of half-open connections; enlarging the backlog lets the server hold more pending SYNs so legitimate clients can still complete the three-way handshake before the queue overflows. Option D (SYN cookies) is correct because it eliminates the need to store half-open state: the server encodes connection parameters into the SYN-ACK sequence number and only allocates resources when the final ACK returns, so spoofed SYNs cannot exhaust memory. Option A (Enabling IP routing) is unrelated to SYN flood mitigation and would only forward packets between interfaces, potentially worsening exposure. Option B (Using UDP instead of TCP) is not a defense—SYN floods are specific to TCP's handshake, and switching protocols changes the application entirely rather than protecting it. Option E (Disabling TCP timestamps) has no effect on SYN flood resistance; timestamps are an optional TCP extension for RTT measurement and PAWS, not a resource-exhaustion control.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enabling IP routing
Why it's wrong here
Enabling IP routing lets the host forward packets between interfaces; it does not reduce half-open connections and can widen exposure. It is tempting because it sounds like traffic control, but routing is the correct setting when the device must act as a gateway between subnets, not as SYN flood protection.
- ✗
Using UDP instead of TCP
Why it's wrong here
UDP is connectionless and not subject to SYN floods, but it changes the protocol.
- ✓
Increasing the SYN backlog queue size
Why this is correct
Enlarging the SYN backlog queue lets the server hold more half-open connections before exhausting the table, absorbing bursts rather than dropping legitimate handshakes. It directly mitigates the stem's SYN flood constraint by raising the volume of pending requests the TCP stack tolerates.
- ✓
SYN cookies
Why this is correct
SYN cookies encode connection state in the sequence number instead of allocating a backlog entry, so the server never stores half-open connections. This defeats the stem's SYN flood constraint by removing the resource exhaustion the attack depends on.
- ✗
Disabling TCP timestamps
Why it's wrong here
TCP timestamps are an optional header extension used for round-trip measurement and PAWS, so disabling them leaves the SYN backlog exhaustion mechanism untouched. It is tempting because it alters TCP behaviour, but timestamp removal is the correct action when troubleshooting middlebox or NAT timestamp issues.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official ISC2 exam blueprint
This SSCP practice question is part of Courseiva's free ISC2 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 SSCP exam.