We have 2 servers one in London and other in Budapest that both have SSH Tectia Server 4.0.5.
We are experiencing very slow file transfer speeds 1.1MBps using "scp" command. we invstigated with our N/W expert and it boiled down to tcp window scaling.
When we tried the same transfers between 2 servers with OpenSSH_3.6.1 the speed between London to Budapest for "scp" file transfer was 2.1MBps
When we tried a transfer from server with OpenSSH_3.6.1 to Server with SSSH Tectia, the server with OpenSSH showed in Network capture that it was asking for tcp a window of 5840 with scaling of 7 (which means multiply by 128) = 747520; but SSH tectia server responds back with window of 49680 (with scaling of 0, which means multiply by 1).
We also confirmed that "ndd /dev/tcp tcp_wscale_always" is set to 1 that is enabled.
Questions are: 1. How do we enable or force SSH Tectia to perform tcp window scaling? 2. Are latest versions of Tectica allow tcp window scaling? 3. Is there any other way to make file transfer run faster on SSH Tectia Server 4.0.5
Thanks Samir Oracle DBA
asked Oct 22 '10 at 15:51