Ok, the transfer that is stalling is caused by the process using port 8094

  5.502271  130.1.1.118 -> 130.1.1.45   TCP [TCP ZeroWindow] 8094 > 59561 [ACK] 
Seq=1 Ack=56809 Win=0 Len=0 TSV=163928420 TSER=311968938

Which would be (accroding to lsof | grep TCP | grep 8094) PID 11561

# ps -ef | grep 11561
root     11561 10625  6 Nov18 ?        11:21:26 /opt/nsr/nsrmmd -n 2

strace reveals FD 7

01:11:02.593016 write(7, "\0\0\0\0XL0305           NETWORKER                    
                             3\0\0\0\0\0\0\0\0\0\0\0\

which finally boils down to the tape drive

# lsof -p 11561 | grep 7u
nsrmmd  11561 root    7u   CHR     9,128      0t0     6489 /dev/nst0

I also found this.
http://www.mibus.org/2012/11/11/networker-random-stalling/
Not sure though if just killing nsrmmd is a solution..

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