SK0-004 · Question #288
A server is connected to a gigabit Ethernet switch and has negotiated 1Gbps / Full Duplex. When transferring large files to and from other servers on the segment via FTP slow performance is noticed…
The correct answer is C. Increase the TCP window size. TCP window size controls how much unacknowledged data can be in transit at once. A small window size causes the sender to stall waiting for ACKs, severely limiting throughput on high-bandwidth connections.
Question
A server is connected to a gigabit Ethernet switch and has negotiated 1Gbps / Full Duplex. When transferring large files to and from other servers on the segment via FTP slow performance is noticed. All network cabling, network hardware and server hardware were verified to be working correctly. Which of the following could be done to improve performance?
Options
- ADecrease the TCP window size.
- BIncrease the UDP window size.
- CIncrease the TCP window size.
- DDecrease the UDP window size.
How the community answered
(45 responses)- A4% (2)
- B13% (6)
- C78% (35)
- D4% (2)
Why each option
TCP window size controls how much unacknowledged data can be in transit at once. A small window size causes the sender to stall waiting for ACKs, severely limiting throughput on high-bandwidth connections.
Decreasing the TCP window size would force more frequent ACKs and further reduce throughput, making the slow performance worse.
FTP uses TCP, not UDP, so adjusting a UDP window size has no effect on FTP transfer performance.
The TCP receive window defines the maximum amount of data a sender can transmit before receiving an acknowledgment. On a gigabit link transferring large files, a small default window size creates a bottleneck because the sender must pause and wait for ACKs frequently. Increasing the TCP window size (or enabling window scaling per RFC 7323) allows more data to be in flight simultaneously, fully utilizing the available bandwidth.
FTP operates over TCP, not UDP, so decreasing a UDP window size is irrelevant to the described scenario.
Concept tested: TCP window size and large file transfer throughput
Source: https://learn.microsoft.com/en-us/troubleshoot/windows-server/networking/slow-ftp-file-transfer-if-tcp-receive-window-is-too-small
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