SSH works well but scp/rsync hangs!!!!

[Mingfan Lu <mingfan.lu@xxxxxxxxx>]

Two machine M1 and M2

 *** in M1
  scp file M2:/dir
  Although it shows the file 100% transferred but scp hangs, I have to
use ctrl c to quit.
  use -vvv options, I can get vvv.log as attachment.
  It is very strange that scp only hangs when the size of file larger
than 1405B , if the size <=1405B, scp works well.
  the attachment diff.log is the difference of the two logs of strace
(to sshd and its forks (process A and process B is the replacement of
forks) )
  The former (s1.log) is the strace log when transferring 1405B file
and the later (s2.log) is for 1406B
  PS. I can use ssh to login M2 successfully.
  *** In M2
  scp file M1:/dir
  it works well!

  Any ideas?

Attachment: diff.log
Description: Binary data

Attachment: s1.log
Description: Binary data

Attachment: s2.log
Description: Binary data

Attachment: vvv.log
Description: Binary data