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I have a strange problem using a tunnel device with new OpenSSH versions. I have the newest OpenSSH 7.3p1 (Debian) client and server side running with the newest Linux kernel (4.7.0), also from the Debian repository.

I can use the ssh server with tunnel devices from clients with older OpenSSH and older Linux kernel version. From the recent client I can use tunnel devices with ssh servers which are older, too.

My problem is, if I try to connect from the newest client programs to the newest server, than I got (with -vvv) the following error message, after configuring the tunnel device

# ifconfig tun1 10.1.1.1 pointtopoint 10.1.1.2
debug2: channel 0: write failed
debug2: channel 0: close_write
debug2: channel 0: chan_shutdown_write: shutdown() failed for fd 5: Socket operation on non-socket
debug2: channel 0: output open -> closed

The tunnel is not working, it means, packets are able to see with tcpdump server side from the client but no one packet is sent from the server back to the client. As the server can be used from an older client (OpenSSH 7.1p2 with kernel 4.4.0 works; OpenSSH 7.2p2 with kernel 4.5.0 does not work, too), it can not be related to the server. Otherwise it can also not be the client, because with older server version it works fine, too. Are there any hint to solve these strange issue? There is not iptables which blocks traffic.

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  • This isn't a security question; it's a systems administration question. I've voted to migrate to SuperUser.
    – Polynomial
    Oct 27, 2016 at 11:01
  • With OpenSSH 7.4p1 the problem still exists.
    – Micha
    Jan 11, 2017 at 12:11

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