In Windows 7 Pro the registry options don't appear to have any affect on the length of the TCP header. in the CurrentControlSet/TCIP/Parameters setting SackOpts = 0 is supposed to turn off selective acknowledgments, but isn't when looking at packet captures. This also applies to tcp1234 for turning off the other TCP header options... how can I turn the tcp header options off?

Hi, How do you know that the option is no avail? I also tried this on my personal computer, the following is the captured frame which captured by myself, you can see the value of Ack significant is set to 1. Frame: Number = 787, Captured Frame Length = 90, MediaType = ETHERNET + Ethernet: Etype = Internet IP (IPv4),DestinationAddress:[00-**********],SourceAddress:[D4-8***********] + Ipv4: Src = 157*, Dest = 157.*, Next Protocol = ESP, Packet ID = 17303, Total IP Length = 76 + Esp: Next Protocol = TCP, SPI = 0x4a3f0884, Seq = 0x3 - Tcp: [Keep alive ack]Flags=...A...., SrcPort=58845, DstPort=52226, PayloadLen=0, Seq=2376607458, Ack=2383729472, Win=65518 SrcPort: 58845 DstPort: 52226 SequenceNumber: 2376607458 (0x8DA826E2) AcknowledgementNumber: 2383729472 (0x8E14D340) + DataOffset: 128 (0x80) - Flags: ...A.... CWR: (0.......) CWR not significant ECE: (.0......) ECN-Echo not significant Urgent: (..0.....) Not Urgent Data Ack: (...1....) Acknowledgement field significant Push: (....0...) No Push Function Reset: (.....0..) No Reset Syn: (......0.) Not Synchronize sequence numbers Fin: (.......0) Not End of data Window: 65518 Checksum: 0x39F8, Disregarded UrgentPointer: 0 (0x0) - TCPOptions: + NoOption: + NoOption: - SACK: type: SACK. 5(0x5) Length: 10 (0xA) - Blocks: -1911237825~-1911237824 LeftEdge: 2383729471 (0x8E14D33F) RightEdge: 2383729472 (0x8E14D340) You may post the frame here, let us check it. Because I found that the registry key already removed by default, so I assume this function can not be controlled by this key. Maybe this no longer can change and turned off by design. The following link for your reference. Thanks.Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.