[yocto] TCP Window Issue while doing SSH

[Ashish Dalela]

Hi,

I'm seeing a TCP window issue while doing a SSH. Below is TCPDUMP capture
of SSH from Yocto to an external Linux server. Yocto sends a SYN window of
14600 (10x of MSS) and external Linux server ACKs with Window of 5792 (4x
of MSS). Now, Yocto Linux drops the ACK.

When I do the SSH from external Linux server the same thing happens and
Yocto Linux never sends out a SYN ACK.

19:00:17.309270 IP 9.1.2.1.40144 > 9.1.1.5.ssh: S 1858484743:1858484743(0)
win 14600 <mss 1460,sackOK,timestamp 130112 0,nop,wscale 5>
19:00:17.309282 IP 9.1.1.5.ssh > 9.1.2.1.40144: S 606474867:606474867(0)
ack 1858484744 win 5792 <mss 1460,sackOK,timestamp 3722481670
115037,nop,wscale 7>

I'm using 9.0.1 but I have faced the same issue with 9.0.2 as well. I tried
turning off TCP window scaling with sysctl -w
"net.ipv4.tcp_window_scaling=0" but it does not help.

Any suggestions on how I can fix this problem? The SSH works fine when the
peer accepts the Window size proposed by Yocto Linux but fails when the
peer proposes an alternate Win size.

Thanks
-Ashish
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