We are having some issues with several clients running Windows 10 downloading files from our HTTP file delivery server. We can’t reproduce the error on our end but notice that TCP window scaling is not “ramping up” and throughput between the Linux server and Windows 10 client remains low. We have run a TCPDUMP on … Read more
There is TCPMSS target to edit MSS value of connections (including forwarded). How to edit window size (for example, cap to some maximum value) by iptables rule? Expecting something like iptables -t mangle -A OUTPUT -p tcp –dport 1234 -j TCPWINDOW –tcpwindow-set ‘min(val,100000)’ Answer To change TCP window from iptables you need to: checkout https://github.com/p5n/ipt_tcpwin … Read more
The TCP window size is the amount of data that the sender will send before waiting for a TCP ack. Does the receiver have a way to control this (e.g., as part of the TCP handshake), or is it only the sender who can control? Answer Yes the receiver can dynamically control the TCP window … Read more
In an effort to prevent DDOS attacks I followed suggestions to leave /proc/sys/net/ipv4/tcp_syncookies value set to 1 in my linux box to enable TCP syncookies. However, when I look at this URL: http://ckdake.com/content/2007/disadvantages-of-tcp-syn-cookies.html It tells me that if I enable tcp_syncookies then half the tcp features including large window management will be disabled which could … Read more
I have a very odd issue with our cisco firewall, If on our osx machines we run the following to disable window scaling support: sudo sysctl -w net.inet.tcp.rfc1323=0 We see near 40% improvement in download speeds (tested using varying linux iso image mirrors). If I sit my machine directly onto the outside modem (Manually setting … Read more
I have a really strange one. I have packet loss with Excessive ‘TCP Dup ACK’ & ‘TCP Fast Retransmission’ when I download files (and only download) from two different Windows 2008 servers. Upload speed is fine. This ONLY occurs if the client computers(Win7) is connected at 100mb/s. At 1GB, no errors and I get full … Read more
A satellite connection generally has a RTT around 500ms. Connections generally suffer sub-optimal transfer speeds, in spite of large amounts of bandwidth because TCP acknowledgements take too long to arrive. My understanding is that a good way to address this problem with TCP connections is to set the TCP Window size to the connection speed … Read more
Facts (please identify any false statements): I have a 100 Mbps connection between two sites that are 80 ms apart This is a long fat connection that could benefit from a large TCP window size perhaps up to 100 Mbps * 0.08 sec = 1,000,000 bytes Both machines are running Windows Server 2012. “Receive window … Read more
