How to force TCP window scaling using SSH?

Question

Inter continent data transfer's speed is maximum 2MB/s.

I checked and the SSH server of my server doesn't even use window scaling, and the window itself is very small, around 22KB...

Flags [S], seq 1433200120, win 29200, options [mss 1420,sackOK,TS val 1451891061 ecr 0,nop,wscale 7], length 0 Flags [S.], seq 3549718494, ack 1433200121, win 65535, options [mss 1460,sackOK,TS val 4214039974 ecr 1451891061,nop,wscale 9], length 0 

Server is 65535*9=590 KB

Window scaling is enabled.

$ cat /proc/sys/net/ipv4/tcp_window_scaling 1 

And I've already increase all the parameters to 25MB and 16MB minimum an default in /etc/sysctl.conf:

net.core.wmem_max=25165824 net.core.rmem_max=25165824 net.ipv4.tcp_rmem = 16777216 16777216 25165824 net.ipv4.tcp_wmem = 16777216 16777216 25165824 

I'm using Fedora 39 and RHEL 8, what can I do to force the SSH server to handle much more inflight data?

Answer 1

So the point is the latency between the end-points which hits TCP quite bad for bandwidth consumption, and therefore you try to go ahead with the TCP window scaling.

About 10 years back i also had issues transferring TBs of data across the glob and if you can not head for block based replication and therefore stuck with filesystem structure scans and copy, you may checkout bbcp.

http://pcbunn.cithep.caltech.edu/bbcp/using_bbcp.htm (disclaimer: i am not taking responsibility for the content of the link)

Those days it was quite helpful as it also can utilize with the parallel streams the full WAN capacity and works similar as scp.

In the end this was also the reason why i stopped it, as on leased lines one is not alone, you have to anyway align with the network operations center, either on bandwidth limits or on quality of service definitions of your traffic, in the end - technical feasible - but not sustainable.