How do I troubleshoot scp timeouts when ssh and sftp seem to work fine?

Question

Keep in mind, ssh works fine... I can run top all day long and never get disconnected. SFTP works fine too! This problems only effects SCP. When I try to SCP a file, it begins tranferring and every time, within 30 seconds it will reset the scp session. A debug of scp looks like this:
.....
debug2: channel 0: rcvd adjust 81920
debug2: channel 0: rcvd adjust 81920
debug2: channel 0: rcvd adjust 81920
debug2: channel 0: rcvd adjust 73728
debug1: channel 0: free: client-session, nchannels 1
debug3: channel 0: status: The following connections are open:
#0 client-session (t4 r0 i0/8192 o0/0 fd 4/5 cfd -1)

debug3: channel 0: close_fds r 4 w 5 e 6 c -1
debug1: fd 0 clearing O_NONBLOCK
debug1: fd 1 clearing O_NONBLOCK
Read from remote host attmatdc3wapi01: Connection timed out
debug1: Transferred: stdin 0, stdout 0, stderr 61 bytes in 8.6 seconds
debug1: Bytes per second: stdin 0.0, stdout 0.0, stderr 7.1
debug1: Exit status -1
debug1: compress outgoing: raw data 11219574, compressed 11223746, factor 1.00
debug1: compress incoming: raw data 1715, compressed 937, factor 0.55
lost connection

There are two Juniper ISG2000 firewalls connected to both devices. No other users on these firewalls complain about this issue so I can only assume it's only effecting my networks.

So the question is... What steps would you suggest taking to troubleshoot this issue?

Answer 1

These two lines...



--> Read from remote host attmatdc3wapi01: Connection timed out

--> lost connection



...give a hint. The first thing I would try is forcing a longer timeout condition with the "-o ConnectTimeout=xx" option.



scp -o ConnectTimeout=60 user@server /blablablah



Warning: Not all versions of scp accept this option.



For verification, you may want to trace the connection with a packet sniffer (such as www.wireshark.org) and see what happens at the network layer (lost or duplicate packets or packets arriving too late, etc).



If the timeout condition still occurs with longer timeout settings, it's probably an scp to ssh implementation/incompatibility issue and I would load a new or different scp client.

Answer 2

Ssh Timeout Server Not Responding

Answer 3

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