JNCIA-SEC Srx Series Service Gateways Practice Question
An engineer is analyzing traffic flow mechanics on an SRX Series gateway. A TCP packet arrives that does not match any existing session in the session table. What is the immediate default action taken by the SRX flow module for this first packet?
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
✓
A session is created in the session table, and the packet is processed against security policies.
When the first packet of a new session arrives, the SRX performs a route lookup, evaluates security policies, and if permitted, allocates a session entry in the session table before forwarding the packet.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A session is created in the session table, and the packet is processed against security policies.
Why this is correct
The SRX evaluates the security policy and creates a session state entry in the session table upon a successful match and permit action.
- ✗
The packet is immediately dropped by the screen check mechanism until a reverse flow is established.
Why it's wrong here
Screen checks happen early, but valid packets are not dropped simply because a reverse flow does not yet exist.
- ✗
The packet is forwarded transparently through the data plane, and the session table is updated only upon session termination.
Why it's wrong here
The SRX is a stateful firewall; sessions must be created at the start of the traffic flow, not at termination.
- ✗
The packet is punted to the Routing Engine for static route validation and ARP resolution before session creation.
Why it's wrong here
Initial packet processing and session creation happen in the PFE/flow module, not by punting every first packet to the Routing Engine.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed August 2026 · checked against the official Juniper Networks exam blueprint
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