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I have a WinXP box (called PETER) with Cygwin installed. This is its version:

C:\bin> uname -a
CYGWIN_NT-5.1 peter 1.7.24(0.269/5/3) 2013-08-15 11:55 i686 Cygwin

I have installed SSHD on it for years and everything worked well. Recently I have changed the router from Speedport 722V to Speedport 921V (I needed IPv6). I have properly set port forwarding rules and they seem to work.

Now I have this strange effect:

  • users from the Internet can connect;
  • I can connect via SSH to my Uni, from there connect to PETER;
  • I can connect to PETER to its local IP address;
  • but I can not connect to it by using the public IP address (which is delivered by dyndns.com) or the DNS name.

I have checked that the IP address is correct. It doesn't work for both the DNS name and the numerical IPv4 address. Port forwarding works: Internet users can connect and as the log file shows, I can connect, but my connection is reset, i.e. actively terminated.

This is the SSH output when I try it:

C:\> ssh -vvvv
OpenSSH_6.2p2, OpenSSL 1.0.1e 11 Feb 2013
debug1: Reading configuration data /etc/ssh_config
debug1: /etc/ssh_config line 61: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to [] port 22.
debug1: Connection established.
debug3: Incorrect RSA1 identifier
debug3: Could not load "/cygdrive/c/text/id_rsa" as a RSA1 public key
debug1: identity file /cygdrive/c/text/id_rsa type 1
debug1: identity file /cygdrive/c/text/id_rsa-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.2
ssh_exchange_identification: read: Connection reset by peer

I only get this eventvwr output: ... sshd: PID 720: Comparing to (p4FDF19DA.dip0.t-ipconnect.de:p4FDF19DA.dip0.t-ipconnect.de).

This is my sshd_config:

Port 22
AddressFamily inet
#ListenAddress ::

# The default requires explicit activation of protocol 1
#Protocol 2

# HostKey for protocol version 1
#HostKey /etc/ssh_host_key
# HostKeys for protocol version 2
#HostKey /etc/ssh_host_rsa_key
#HostKey /etc/ssh_host_dsa_key
#HostKey /etc/ssh_host_ecdsa_key

# Lifetime and size of ephemeral version 1 server key
#KeyRegenerationInterval 1h
#ServerKeyBits 1024

# Logging
# obsoletes QuietMode and FascistLogging
#SyslogFacility AUTH
LogLevel INFO

# Authentication:

#LoginGraceTime 2m
#PermitRootLogin yes
StrictModes no
#MaxAuthTries 6
#MaxSessions 10

#RSAAuthentication yes
#PubkeyAuthentication yes
#AuthorizedKeysFile .ssh/authorized_keys

# For this to work you will also need host keys in /etc/ssh_known_hosts
#RhostsRSAAuthentication no
# similar for protocol version 2
#HostbasedAuthentication no
# Change to yes if you don't trust ~/.ssh/known_hosts for
# RhostsRSAAuthentication and HostbasedAuthentication
#IgnoreUserKnownHosts no
# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes

# To disable tunneled clear text passwords, change to no here!
PasswordAuthentication no
PermitEmptyPasswords no

# Change to no to disable s/key passwords
ChallengeResponseAuthentication no

# Kerberos options
#KerberosAuthentication no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
#KerberosGetAFSToken no

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

# Set this to 'yes' to enable PAM authentication, account processing, 
# and session processing. If this is enabled, PAM authentication will 
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
#UsePAM no

#AllowAgentForwarding yes
#AllowTcpForwarding yes
#GatewayPorts no
#X11Forwarding no
#X11DisplayOffset 10
#X11UseLocalhost yes
#PrintMotd yes
#PrintLastLog yes
#TCPKeepAlive yes
#UseLogin no
UsePrivilegeSeparation yes
#PermitUserEnvironment no
Compression yes

# after 3*2min of no answer from the client, terminate the connection
# so after a hibernation etc. the connection will most likely be dead.
ClientAliveInterval 2m
ClientAliveCountMax 3

#UseDNS yes
#PidFile /var/run/sshd.pid
#MaxStartups 10
#PermitTunnel no
#ChrootDirectory none

# no default banner path
#Banner none

# override default of no subsystems
Subsystem   sftp    /usr/sbin/sftp-server

# Example of overriding settings on a per-user basis
#Match User anoncvs
#   X11Forwarding no
#   AllowTcpForwarding no
#   ForceCommand cvs server

To make things more obscure, I "fixed" this problem the other day by modifying the /etc/hosts.allow file, but this "fix" doesn't work any more. It was not needed anyhow for the last years, so I'm all the more confused. The other day I was under the impression that the router might reverse-resolve the IP number to a name, something the old router maybe did differently than the new one??

Does anyone have any idea? I'm clueless, but I don't really understand all of the workings (e.g. the /etc/hosts.allow and .deny files are new to me).

More info: It doesn't work even with empty hosts.allowand .denyfiles. SSHD DEBUG3 logging doesn't show any reason for disconnect. Right now, I think it's a hardware problem with the router...

share|improve this question
Did you set up the same port forwarding in the new router? Do other services work fine? –  golimar Sep 3 '13 at 15:53
There are no other services, but I can connect from the outside, so port forwarding must be working OK. –  cxxl Sep 3 '13 at 15:57
Do I get your setup right: PETER - SPEEDPORT - INTERNET - UNI? Where do ,,users from the internet'' can connect to -- to the cygwin sshd? You ssh'd into UNI only for testing purposes, to check if you can connect to PETER from the ,,outside''?! –  mpy Sep 4 '13 at 15:56
"Users from the Internet" is anyone connected to the Internet and to check that, I connect to Uni and test from there. The "normal" user would just connect from his workplace on the Internet (no Uni). –  cxxl Sep 4 '13 at 16:34
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