On 12/14/11, David Groves wrote: > I am having some issues with cygwin applications (specifically sshd) > and TCP Window Scaling Factors. I am using OpenSSH client on either a > Debian Linux or FreeBSD machine to connect to sshd on a Windows 2k8 R2 > server. > > My SYN from the client has a non-zero WSF (16 for Debian, 8 for > FreeBSD), but the SYNACK response from the windows box has 0 as the > WSF. This means I will have a maximum of 64Kbytes of traffic allowed > to be unacknowledged in the TCP window. This is causing me > considerable performance problems in transfers from Europe to the US > West Coast and Australia. > > To try and decide if cygwin was a factor in this, I tried to replicate > this with Apache2 and pure-ftpd on cygwin, and in both cases, the WSF > was 0. I then tried a non-cygwin Apache2 install, and it returned a > non-zero WSF. > > TCP settings is clearly a function of the OS, but I'm a little unsure > where the line is drawn between the OS with cygwin, and it is > interesting I can reproduce this with multiple cygwin apps, and I > cannot reproduce it with non-cygwin apps, I'm thinking cygwin is at > least somewhat involved as part of the problem. > > Anyone have any ideas/pointers ?
No pointers, but it does look like a Cygwin problem. Start up wireshark on a Windows XP machine and ssh (from a cygwin window) to another machine - tcp syn packet has a window size of 65535 and a widow scale of zero. Use putty from the dos prompt to ssh to the same machine and that has a window size of 65535 and a window scale of 2 Lee -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
