What is a primary characteristic of traffic shaping?

350-401 By islever Editorial Last updated Aug 2, 2026

Short answer

B must be applied only to outgoing traffic

Question

What is a characteristic of traffic shaping?

lacks support for marking or remarking
must be applied only to outgoing traffic Correct Answer
can be applied in both traffic directions
queues out-of-profile packets until the buffer is full

Key Takeaways

This question tests your understanding of the directional limitations and operational mechanics of traffic shaping versus policing, with the common trap being the misinterpretation of how shaping handles out-of-profile traffic.

Traffic shaping is a QoS mechanism designed to control outbound data rates by buffering and delaying packets to match a configured profile. The community consensus strongly supports option B, emphasizing that shaping is fundamentally restricted to egress interfaces, unlike policing which can operate bidirectionally.

Common mistake: Candidates frequently choose D, mistakenly believing shaping passively queues packets until the buffer reaches capacity. In reality, shaping actively regulates traffic flow by introducing controlled latency to conform to rate profiles, and its defining architectural constraint is its exclusive egress application.

Expert Analysis

Core Concept: Egress-Only Operation

Traffic shaping is strictly an outbound/egress mechanism. As noted in multiple Cisco documentation references cited by candidates, shaping requires a buffer to hold and delay packets so they can be transmitted at a controlled rate. Because incoming traffic arrives at line speed and must be processed or dropped immediately upon interface ingress, there is no practical way to apply shaping on the inbound direction. This makes Option B definitively correct and Option C incorrect. A useful exam mnemonic is "Police inbound & Shape outbound."

Why Other Options Are Incorrect

Option A: Shaping fully supports marking and remarking (e.g., DSCP or CoS values) either before shaping occurs or as part of the traffic classification process. Marking is independent of the shaping mechanism itself.
Option D: While shaping does buffer out-of-profile traffic, it does not merely queue packets until the buffer is full. Instead, it actively regulates transmission timing by delaying packets to smooth bursts and maintain compliance with the Committed Information Rate (CIR) or Peak Information Rate (PIR). Describing it as passive queuing until buffer exhaustion confuses shaping with simple tail-drop queuing or misrepresents its latency-inducing, rate-matching behavior.

Shaping vs. Policing Context

Understanding the directional and behavioral differences between shaping and policing is critical for the ENCOR exam. Policing enforces limits by dropping or remarking excess traffic without adding significant delay, making it suitable for both ingress and egress. Shaping prioritizes order and latency tolerance by delaying excess traffic, which is why it is architecturally confined to egress interfaces.

Official Reference

These links open the official vendor documentation in a new tab.

Exam Strategy

When evaluating QoS questions, always distinguish between shaping (delays/buffers, egress-only, latency-tolerant) and policing (drops/remarks, bidirectional, latency-sensitive). Use the directional rule of thumb to eliminate options quickly, and scrutinize wording around buffering—shaping regulates flow through controlled delay, not passive fill-and-drop behavior.

Community Votes

54%

46%

54% of anonymous learners picked answer B. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 13 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 13

babanaber 👍 6 Answered D

https://www.cisco.com/c/en/us/support/docs/switches/catalyst-4000-series-switches/21263-134.html#:~:text=Traffic%20shaping%20buffers%20out%2Dof%2Dprofile%20traffic%20and%20smoothes%20traffic%20bursts%2C%20but%20affects%20the%20delay%20and%20delay%20variation.%20Shaping%20can%20only%20be%20applied%20on%20an%20outgoing%20interface%2C%20while%20policing%20can%20be%20applied%20on%20both%20incoming%20and%20outgoing%20interfaces.
pacman64 👍 4 Answered B

The correct answer is B: Traffic shaping must be applied only to outgoing traffic. Here's the explanation: Traffic shaping is fundamentally an outbound-only mechanism because: - It can only control traffic as it leaves an interface - It cannot shape traffic that is incoming to an interface - It requires a buffer to hold and delay packets, which only works on egress Why other options are incorrect: A) Lacks support for marking or remarking - Incorrect because traffic shaping can work in conjunction with marking/remarking mechanisms - Many implementations support both shaping and marking capabilities C) Can be applied in both traffic directions - Incorrect as explained above - shaping only works on outbound traffic - For inbound traffic control, policing would be used instead D) Queues out-of-profile packets until the buffer is full - Incorrect because traffic shaping will drop packets if the buffer becomes full - It doesn't simply queue indefinitely - When buffers are full, tail-drop or other configured drop mechanisms are implemented
falconer42003 👍 4 Answered B

Shaping is for outbound traffic. https://www.cisco.com/c/en/us/support/docs/quality-of-service-qos/qos-policing/19645-policevsshape.html
EAC84 👍 3

B https://www.cisco.com/c/en/us/support/docs/quality-of-service-qos/qos-policing/19645-policevsshape.html [ Selection Criteria] "Controls bursts and smooths the OUTPUT rate over at least eight time intervals."
wengzaii96 👍 3

i think should be C Traffic shaping can be used to manage and prioritize traffic flow on both incoming and outgoing network interfaces.

Show 8 more comments

NetworkJanitor 👍 2 Answered B

"Police inbound & Shape outbound" as a general rule B if you are going by what Cisco is stating: "Shaping can only be applied on an outgoing interface, while policing can be applied on both incoming and outgoing interfaces." Google search that string for multiple returns supporting that statement.
RickAO76 👍 2 Answered C

D - wrong Does not Queue out-of-profile packets - it regulates the rate of traffic flow by delaying/shaping to match traffic profile
cwauch 👍 2 Answered B

Is everyone avoiding the fact that B - must be applied outbound only, is a strong characteristic of shaping?
matass_md 👍 1 Answered D

While B is a valid point , that in general shaping is done on the egress interface we need to think what shaping does in the first place . Shaping puts packets in the buffer that go over the CIR (Committed Information Rate) , Shaping introduces latency . This being said , out-of-profile means traffic that goes over CIR . We have CIR PIR . Draw a line note is as CIR then a line above as PIR (Peak Information Rate) Everything thats above CIR gets shaped(buffered) , , what goes above PIR gets dropped.
d4c4159 👍 1 Answered D

Since Traffic shaping can't apply marking A is wrong. Since Traffic shaping is an outbound only service that makes B & C Wrong. Thus making D the only option for a correct Answer, although watch the wording because it only uses that wording in the Supervisor documentation, is the general Traffic Shaping documentation it states it just controls the flow.
[Removed] 👍 1

C is correct. D also is correct. out and in
RickAO76 👍 3 Answered D

-Official changing vote to D
Nikolas123 👍 3 Answered B

B is correct

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