SSH Disconnects

felix001 · 12-12-2011, 07:38 AM

Im currently connecting to 2 Linux servers over my remote access VPN via SSH.
Once server is fine, the other keeps disconnecting at random times sometimes after a few seconds idle, sometimes after a few minutes.
Ive run a debug on the SSH daemon and can see it say,

"Read error from host x.x.x.x: Connection reset by peer"

Ive checked the networking on the problematic box but everything appears fine speed/duplex/interface errors.

Does anyone have any ideas ??

soonblue · 12-12-2011, 03:55 PM

Are you connecting to these two servers from a Linux box or a Windows box using putty or something similar? I have seen weird behavior before with some servers when not sending KEEPALIVE packets every thirty seconds or so. You can edit the ServerAliveInterval on Linux to accomplish the same thing. Alternatively, take a look at your sshd_config file on the servers and lower ClientAliveInterval. This will send a packet to your client during inactivity. It may take a little tweaking. Also, how are the firewalls on your servers and client configured?

Blue

University of Delaware
Network & Systems Services
Systems Programmer III

felix001 · 12-13-2011, 11:46 AM

Hey,

Im logging in from a windows box. Typically using putty.
The firewalls between me and the server should be fine since I can connect to other linux servers on the same network without any issues/disconnects.

Its strange as Ive logged onto millions of Linux servers in the past but never has this issue(??).
Ive added a 1 sec Interval to the sshd config so will test this and let you know how it goes.

Is there anything odd in the config that you can see.

Code:

PasswordAuthentication no
#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

# This is enabled, PAM authentication is allowed through the
# ChallengeResponseAuthentication and PasswordAuthentication.
#UsePAM no
UsePAM yes

AllowTcpForwarding no
#GatewayPorts no
#X11Forwarding no
#X11DisplayOffset 10
#X11UseLocalhost yes
#PrintMotd yes
#PrintLastLog yes
TCPKeepAlive yes
#UseLogin no
#UsePrivilegeSeparation yes
#PermitUserEnvironment no
#Compression delayed
#ClientAliveCountMax 3
ClientAliveInterval 1
ClientAliveCountMax 10
UseDNS no
#PidFile /var/run/sshd.pid
#MaxStartups 10
#PermitTunnel no


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

linuxrndblog · 12-15-2011, 04:16 AM

Dear felix001,

I have understood your problem. Just put the below option in sshd_config file under /etc/ssh/ directory.

ClientAliveInterval 180

[root@localhost ~]# cd /etc/ssh/
[root@localhost ssh]# pwd
/etc/ssh
[root@localhost ssh]# ll
total 200
-rw------- 1 root root 132839 Mar 31 2010 moduli
-rw-r--r-- 1 root root 1827 Mar 31 2010 ssh_config
-rw------- 1 root root 3324 Nov 18 18:30 sshd_config
-rw------- 1 root root 668 Nov 17 00:49 ssh_host_dsa_key
-rw-r--r-- 1 root root 590 Nov 17 00:49 ssh_host_dsa_key.pub
-rw------- 1 root root 963 Nov 17 00:49 ssh_host_key
-rw-r--r-- 1 root root 627 Nov 17 00:49 ssh_host_key.pub
-rw------- 1 root root 1675 Nov 17 00:49 ssh_host_rsa_key
-rw-r--r-- 1 root root 382 Nov 17 00:49 ssh_host_rsa_key.pub
[root@localhost ssh]#

felix001 · 12-15-2011, 08:16 AM

I tried this setting but the connection still times out

(

deep27ak · 12-16-2011, 10:57 PM

try this

Code:

#vi /etc/ssh/ssh_config
ServerAliveInterval 60---->(add this line)

Code:

#cd ~/.ssh/config ------>create this file if doesnot exist
Host *
 ServerAliveInterval 60

NOTE: start the second line in this file after a space

or add your server's hostname

Code:

Host server.example.com
 ServerAliveInterval 60

restart the ssh server

novice06 · 12-17-2011, 07:47 AM

This is very common problem and very difficult to trace. It could be because of internet link, firewall, vpn.
Workaround:
If you are only shell access to server, one easy way to overcome this is use "screen" utility. connection broken when you are doing something, after reconnect just reattach

linuxrndblog · 12-19-2011, 07:25 AM

Dear felix001,

Are you resolve this issue? or still facing same issue?

felix001 · 12-20-2011, 07:16 AM

Im still having the same issue

(

deep27ak · 12-20-2011, 07:17 AM

Quote:

Originally Posted by felix001

Im still having the same issue

(

did you tried what I said?

felix001 · 12-20-2011, 07:59 AM

Yes Im afraid I did, but still no luck.

felix001 · 12-23-2011, 10:27 AM

I ran a packet capture and can see a RST being sent from the server ??
Any other ideas anyone.