Cisco SD-WAN TCP Optimization Functions
Short answer
BC The Cisco SD-WAN TCP optimization tool uses TCP selective acknowledgment (SACK) and terminates TCP connections locally at the WAN edge.
Question
Key Takeaways
The question tests knowledge of TCP optimization components: SACK for efficient retransmission and local termination to bypass WAN congestion.
This question examines the specific mechanisms of Cisco SD-WAN TCP optimization, focusing on its use of Selective Acknowledgment (SACK) and local connection termination at the WAN edge. The correct options highlight how these features improve throughput by managing window sizes and reducing latency.
Common mistake: Many candidates choose option D (remote termination), incorrectly assuming a dual-ended proxy is required or that termination happens at both ends, whereas the feature primarily terminates locally to optimize the path.
Expert Analysis
Why the Answer Is Correct
Cisco SD-WAN TCP optimization works by terminating the TCP connection locally at the WAN edge router (Option C). This creates a proxy-like effect where the SD-WAN device handles the retransmissions over the WAN link instead of the end hosts. Additionally, it utilizes TCP Selective Acknowledgment (SACK) (Option B) to inform the sender about which segments have arrived successfully, allowing for more efficient retransmission of only lost packets rather than entire windows.
Why the Other Options Are Wrong
Option A is too generic; standard TCP uses ACKs, but SACK is the specific optimization feature. Option D is incorrect because while dual-ended proxies are possible, the core function described in the context of 'local' optimization usually refers to the single-ended or primary termination point at the edge closest to the client or as configured, and specifically, the documentation highlights local termination as the key mechanism for the optimization engine itself. Option E is incorrect because TCP optimization is primarily for data traffic throughput, not specifically for control traffic packet loss handling.
Community Comment Notes
Community consensus strongly supports BC, with users noting that the feature terminates connections locally and uses SACK to maximize throughput. One user referenced official Cisco documentation confirming that TCP optimization fine-tunes TCP parameters and uses SACK. Another comment mentioned that while dual-ended proxies exist, the fundamental description aligns with local termination and SACK usage.
Official Reference
This link opens the official vendor documentation in a new tab.
Exam Strategy
When studying SD-WAN features, focus on the specific protocols and mechanisms used for optimization, such as SACK and NPTv6. Understand whether a feature operates at the control plane or data plane, and whether it modifies traffic flow directly.
Frequently Asked Questions
Why does TCP optimization terminate connections locally?
What is the role of SACK in this optimization?
Community Votes
80% of anonymous learners picked answer BC. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 7 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 7
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abvga 👍 2The Cisco SD-WAN TCP Optimization feature terminates TCP connections locally at the WAN edge routers and uses TCP Selective Acknowledgment (SACK) in order to better control the TCP-Window-Size and maximize the throughput through the WAN links.
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Zamochit 👍 1It is recommended that you configure TCP optimization on both the routers, the router closer to the client and the router closer to the server. This configuration is sometimes called a dual-ended proxy. "It is possible to configure TCP optimization only on the router closer to the client", a scenario called single-ended proxy, but this configuration is not recommended because the TCP optimization process is compromised. TCP is a bidirectional protocol and operates only when connection-initiation messages (SYNs) are acknowledged by ACK messages in a timely fashion. I dont know... it could be local (at client) and it is using Selective ACK...
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Knowledge33 👍 1The optimization is done between both end routers: https://www.cisco.com/c/en/us/td/docs/routers/sdwan/configuration/optimization-ha/ios-xe-16/network-optimization-high-availability-book-xe/m-tcp-optimization.html#:~:text=This%20feature%20optimizes%20TCP%20data,trip%20latency%20and%20improve%20throughput.
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Gycu 👍 1BC The Cisco SD-WAN TCP Optimization feature terminates TCP connections locally at the WAN edge routers and uses TCP Selective Acknowledgment (SACK) in order to better control the TCP-Window-Size and maximize the throughput through the WAN links
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Tsartipi 👍 1A and C could be correct : https://www.cisco.com/c/en/us/td/docs/routers/sdwan/configuration/appqoe/ios-xe-17/appqoe-book-xe/m-tcp-optimization.html#:~:text=TCP%20optimization%20fine%20tunes%20the,Catalyst%20SD%2DWAN%20devices.
Show 2 more comments
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RafaJohnston76 👍 1Based on this article: https://www.networkacademy.io/ccie-enterprise/sdwan/application-quality-of-experience-appqoe#:~:text=The%20Cisco%20SD%2DWAN%20TCP,throughput%20through%20the%20WAN%20links.
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mikidvd51 👍 1IMHO the SACK feature in TCP is standard for number of years between ordinary TCP hosts. I don't quite understand why is cisco SDWAN pinpointing here this as groundbreaking SDWAN optimization.
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