Remote telnet sessions locks up with larger amount of output

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Connected remotely (through a Sonicwall router) entering commands with a lot of output, such as ls -al or ps -ef, the sessions just locks up. Entering other commands, with less output seem to run fine. If I connect directly from the console I don't have this issue. We have tried lowering the MTU and still have the problem. Not sure if there is a firewall appliance problem or not. We have an AIX box on the same network and never have any problems with it. We are running Red Hat EL 6.4.

Any ides would be greatly appreciated. Thanks

ST
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thomas.jones2@dodiis.mil's picture Guru 6435 points
14 January 2015 6:02 PM

Used to run into issues with some firewalls - particularly NAT'ing firewalls - where you'd see this kind of behavior. Some of them had overrides that you needed to set to avoid this behavior ...but it's been a good ten years since I've had to deal with those peculiarities.

james.radtke@siriusxm.com's picture Guru 6863 points
14 January 2015 6:10 PM

Same here.. except I think mine was even using SSH. Ha - the "good ol' days" ;-) And mine would only happen when I would paste a bunch of text in to the terminal. But, now that you mention it, I think my issue was only when I was VPN'd in. Which points to some sort of network device - I really can't recall what the fix was.

Sandy - does your client have any buffer settings?
Is your RHEL host on the same subnet as the target?
Did you try using nmap (and wireshark) to gather some packets?

thomas.jones2@dodiis.mil's picture Guru 6435 points
14 January 2015 9:43 PM

Yeah. You had to apply fixes for telnet/SSH and fixes for SMTP conversations (and sometimes FTP). Surprised that these things still crop up.

Jamie Bainbridge's picture Red Hat Guru 7257 points
14 January 2015 11:28 PM

My first thought was also MTU. What does a packet capture of the TCP session on each end show?

ST Community Member 85 points
15 January 2015 4:56 PM

I am working with Red Hat support on the issue now. They are looking at tcpdumps.

Everything was working fine going through a Sonicwall to an IBM AIX server. Just started having problems when they went live on the RHEL server and we switched firewall rules to go to it instead of the IBM server. We have cleaned up the firewall rules and recreated for telnet to the RHEL server, but still have the issue.

Thanks for everyone's response.

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