Quick Answer
The answer is QoS pre-classify. This feature is required because when IPsec encrypts a packet, the original IP header—including its DSCP markings—is encapsulated within the tunnel payload, and the tunnel interface generates a new outer IP header with a default DSCP value of zero. By enabling QoS pre-classify on the crypto map or tunnel interface, the router copies the original DSCP value to the outer header before encryption, ensuring that IPsec VPN QoS preserve DSCP markings end-to-end. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of how QoS interacts with VPN encapsulation; a common trap is assuming that marking the tunnel interface itself will carry the DSCP through encryption. Remember: the tunnel header is a fresh header, so pre-classify is the bridge that copies the inner mark to the outer packet. A useful memory tip is “pre-classify copies, post-encrypt is blind.”
This 350-501 practice question tests your understanding of automation and quality of service. 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.
An enterprise uses IPsec VPN to connect branch offices. They apply QoS policies on the tunnel interface but notice that original DSCP markings are not preserved after encryption. Which feature should be enabled to maintain end-to-end QoS?
AutoQoS
Why wrong: AutoQoS automates QoS configuration but does not address IPsec marking.
QoS pre-classify
This feature copies the original DSCP to the tunnel header.
MPLS TE
Why wrong: MPLS TE is for traffic engineering, not marking preservation.
NBAR
Why wrong: NBAR is for application recognition, not marking preservation.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
QoS pre-classify
When IPsec encrypts a packet, the original IP header (including DSCP markings) is hidden inside the tunnel payload. The tunnel interface then applies a new outer IP header, and QoS policies applied to the tunnel interface classify based on the outer header's DSCP, which defaults to 0. Enabling 'qos pre-classify' on the crypto map or tunnel interface copies the original DSCP value to the outer IP header before encryption, preserving end-to-end QoS markings across the IPsec tunnel.
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.
AutoQoS
QoS pre-classify
Why this is correct
This feature copies the original DSCP to the tunnel header.
Related concept
Read the scenario before looking for a memorised answer.
MPLS TE
Why it's wrong here
MPLS TE is for traffic engineering, not marking preservation.
NBAR
Why it's wrong here
NBAR is for application recognition, not marking preservation.
Common exam traps
Cisco often tests the misconception that QoS policies on the tunnel interface automatically see the inner packet's DSCP, but in reality encryption hides the original header, so 'qos pre-classify' is required to copy the marking to the outer header.
Detailed technical explanation
The 'qos pre-classify' feature works by copying the original packet's IP header (including DSCP) to the outer tunnel header before encryption, or by allowing the QoS policy to classify based on the original packet's header before it is encapsulated. This is configured under the crypto map or tunnel interface with the command 'qos pre-classify'. In a real-world scenario, if a branch office uses DiffServ with EF (Expedited Forwarding) for VoIP, without this feature the voice traffic would lose its priority marking after encryption, causing jitter and poor call quality.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the 350-501 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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Automation and Quality of Service — study guide chapter
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FAQ
Automation and Quality of Service — This question tests Automation and Quality of Service — Read the scenario before looking for a memorised answer..
The correct answer is: QoS pre-classify — When IPsec encrypts a packet, the original IP header (including DSCP markings) is hidden inside the tunnel payload. The tunnel interface then applies a new outer IP header, and QoS policies applied to the tunnel interface classify based on the outer header's DSCP, which defaults to 0. Enabling 'qos pre-classify' on the crypto map or tunnel interface copies the original DSCP value to the outer IP header before encryption, preserving end-to-end QoS markings across the IPsec tunnel.
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 25, 2026
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