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clearloon

Member

Registered: 2009-01-07

Posts: 79

ssh using DNS fails after a period of time

Hello -

ssh into my box using a domain name is failing after a period of time (minutes).

It works when  sshd first starts, but then after a period of time it will fail. After failure, I can still ssh in using the hostname, just not using the dyndns name.

I've tried the suggestions at 3.3 here (http://www.openssh.org/faq.html) but have had no result.

I've got no idea why this is happening! Why would it work to start with, but then later fail?

All my packages are current as at today, and sshd_config looks like this:

# OpenBSD: sshd_config,v 1.75 2007/03/19 01:01:29 djm Exp $
# This is the sshd server system-wide configuration file.  See
# sshd_config(5) for more information.
# This sshd was compiled with PATH=/usr/bin:/bin:/usr/sbin:/sbin
# The strategy used for options in the default sshd_config shipped with
# OpenSSH is to specify options with their default value where
# possible, but leave them commented.  Uncommented options change a
# default value.

Port 443
Protocol 2
ListenAddress 0.0.0.0
#ListenAddress ::

# HostKey for protocol version 1
#HostKey /etc/ssh/sshhostkey
# HostKeys for protocol version 2
#HostKey /etc/ssh/sshhostrsa_key
#HostKey /etc/ssh/sshhostdsa_key

# Lifetime and size of ephemeral version 1 server key
#KeyRegenerationInterval 1h
#ServerKeyBits 768

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

# Authentication:

LoginGraceTime 120
PermitRootLogin no
#StrictModes yes
#MaxAuthTries 6

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

# For this to work you will also need host keys in /etc/ssh/sshknownhosts
#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 yes
#PermitEmptyPasswords no

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

# 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 mechanism.
# Depending on your PAM configuration, this may bypass the setting of
# PasswordAuthentication, ~PermitEmptyPasswords, and
# "PermitRootLogin without-password". If you just want the PAM account and
# session checks to run without PAM authentication, then enable this but set
# ChallengeResponseAuthentication=no
#UsePAM no

#AllowTcpForwarding yes
#GatewayPorts no
#X11Forwarding no
#X11DisplayOffset 10
#X11UseLocalhost yes
#PrintMotd yes
#PrintLastLog yes
#TCPKeepAlive yes
#UseLogin no
#UsePrivilegeSeparation yes
#PermitUserEnvironment no
#Compression yes
#ClientAliveInterval 0
#ClientAliveCountMax 3
UseDNS no
#PidFile /var/run/sshd.pid
#MaxStartups 10

# no default banner path
#Banner /some/path

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

Any ideas?

Thanks,

cl

ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 19,876

Re: ssh using DNS fails after a period of time

Any chance someone in the middle is blacklisting you?  Like your company's (your school / your coffee shop) IP department detecting a dynamic DNS and shutting down access?

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clearloon

Member

Registered: 2009-01-07

Posts: 79

Re: ssh using DNS fails after a period of time

possible, however the issue has arisen for both my home and work connections within the last 2 weeks. Seems unlikely they'd both blacklist at the same time. Also, it does work from both initially - it just drops after 30 minutes or so...

R00KIE

Forum Fellow

From: Between a computer and a chair

Registered: 2008-09-14

Posts: 4,734

Re: ssh using DNS fails after a period of time

I would check if you are not getting a new IP after a connection drop, that might cause trouble with dyndns.

Do a dns lookup and check that you get the correct IP and not something like 127.0.0.1 or your previous IP. You can also try to connect using IP only after you start having problems and check if the problem is with dns or something else. Check the logs and look for anything suspicious.

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R00KIE
Tm90aGluZyB0byBzZWUgaGVyZSwgbW92ZSBhbG9uZy4K

clearloon

Member

Registered: 2009-01-07

Posts: 79

Re: ssh using DNS fails after a period of time

Meh. Same thing's happening when I use an IP address. Am investigating router/ISP issues...