SSH connection freezes RedHat

Hi Experts,

I have a Redhat Enterprise server 6.2 with openssh.
The putty connection is always freezing, and this sporadic.

I already checked the switch port for network issues, but I don't see any errors.  I check also the load of server with kSar, but I dont see anything strange.

What could it be? A faulty network card?  Are what can I do to troubleshoot more?
trivinAsked:
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Duncan RoeSoftware DeveloperCommented:
On the server, try tcpdump port ssh (you may need to be root). Post back what happens when a putty connect fails.
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gheistCommented:
For how long it "freezes"? any firewall between you and server? e.g. iptables?
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Gerwin Jansen, EE MVETopic Advisor Commented:
Is your ssh connection the only process that is freezing? Do other users of the system have similar issues? What kind and how many other connections are present when the issues happens? You can check with netstat.
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Jan SpringerCommented:
Try disabling DNS In the /etc/ssh/sshd_config and service sshd reload.
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trivinAuthor Commented:
It is indeed not always, only when there is more load on the server I think.  Because I want to do a dump right now, but I am waiting till it freezes.

When it freezes, it never comes back.

SSH is the only process that is freezing.  

There is indeed a firewall between, but no IP tables.

There are 36 open connections at this moment, when another puty terminal freezed.
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trivinAuthor Commented:
@ Duncan Roe
When I do this command, I just get a blank line when I try to execute this command.  I will try more.

@jesper, I just disabled dns... Let's see if this helps.

Freezing is random, just freezed right after logging in.
Or freezed after doing a netstat command...
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gheistCommented:
The firewall in between is most likely at fault.
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trivinAuthor Commented:
I did restart of the network stack.  The server crashed...  I logged on with DRAC for remote management, and the system was hanging, I had to do a reset of the system.
And it seems to work nice, it does not freeze any more.
But I let this thread open for some days, if the issue comes back or not.
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gheistCommented:
Check dmesg
if it updates any microcodes during boot - please consider updating all dell firmwares/microcodes/bios-es
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Gerwin Jansen, EE MVETopic Advisor Commented:
@gheist - dell?
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gheistCommented:
DRAC == DELL
Also upgrade to RHEL 6.5 would be nice (EUS is till active if you pay it, but not for long)
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Gerwin Jansen, EE MVETopic Advisor Commented:
@gheist - Thanks ;)
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trivinAuthor Commented:
server reboot fixed the issue, but the answer provided helped me to troubleshoot.
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