Telnet session does not always connect and gives a blank window.

[David Wilkins]

Trying to connect to HPUX server from Windows 2000 using Telnet, Putty or CRT will intermitantly give a blank screen.

It seems that for a period of time it will connect on the first attempt sometimes it may take two attempts. Other times it will take three attempts.

Does anyone have any idea as to why?

[Daedalus]

Sounds like you may have a connectivity issue?? Can you ping the HP-UX server and if so do you get any dropped packets?

[David Wilkins]

Yes, I can ping it without any drops.

[John Dvorchak]

when you say "will intermitantly give a blank screen" I am assuming that you are talking about the client end and it just takes a while for the connection. There are only a couple of reasons why this would happen, one is connectivity. It could very well be that a ping works 100% of time but there is still an issue with the LAN. Look at the HPUX box and confirm that the NIC is set the same as the LAN switch port. They traditionally don't like to "auto-negotiate" with switches and should therefore be hard set. 100 full duplex usually works. In a 10 mb LAN this is usually not a problem.

The other issue the delay in connecting may occur because the HPUX box can't immediatley determine the Win2k's name/address from DNS.
Every attempt at telnet, the HPUX box will try to perform an nslookup on the requesting host address. Usually you can tell this is happening because the connection will eventually happen ok but it takes a minute. If that is what you suspect, once you are logged in to a who -mT and see if it gives a name or just and IP address.

[Bill Hassell]

Did you wait for 60 seconds? If the connection finally shows up after 30-60 seconds, you have a reverse lookup failure in your DNS server. HP-UX networking attempts to validate new connections by asking the DNS server if it knows about the incoming IP address. Depending on the settings in /etc/nsswitch.conf, there may be a 20 second timeout waiting for a confirmation. Or in /etc/resolv.conf you have 3 DNS servers and the first two are not reachable so 20 seconds will be burned waiting for each one to timeout.

You can fix this without modifying your DNS servers: change nsswitch.conf to look in hosts first, then go to DNS if not found. Here's the relevant entry:

hosts: files [NOTFOUND=continue UNAVAIL=continue] dns [NOTFOUND=retur
n UNAVAIL=continue TRYAGAIN=return]

Just replace the existing hosts: line with the above 1-liner. That should solve the long delay for initial connection.

[Bill Hassell]

Oops, forgot to mention that you'll need to add names and IP addresses for the problem machines into /etc/hosts for this to work.

[David Wilkins]

If the blank screen happens it happens only when I attempt to start a telnet session. From a command prompt I type "telnet " then it seems as if it connects but I don't get the login information.

This does not change. It will not eventually connect over time. I have left it open for long periods of time just to see if it will eventually connect. It does not.

With this "blank" window still running. I then have to open another command prompt and attempt to connect useing telnet. If it does not work after the second session is open, I then leave the first two "blank" windows open and open a third. The third always works.

I do know the NIC is set to Full-duplex. I'll check the switch.

[Mel Burslan]

it looks like you are having reverse DNS lookup problems as Bill H indicated above. As far as I understand, your first and second telnet windows will eventually connect after sitting blank for about 60 seconds or so. Am I right ?

[David Wilkins]

Mel, I appreciate the input but It will not connect after serveral minutes even hours.

I checked the NIC and switch/router interfaces and found they are all set to full-duplex.

[Bill Hassell]

Get a copy of Ethereal (and winpcap for PCs) so you can trace the connection attempts. Narrow the trace to just the IP address of your Win2k machine and see what's happening with the protocol. You might do a traceroute from the PC to the server and also from the server to the PC when you have problems.

[Navin Bhat_2]

Try to telnet from different systems including the server itself (localhost). Do you see different behaviour patterns?

Try hostname and ip address. Is there a difference?

Check your patch levels for telnetd.

[Navin Bhat_2]

>>>>From a command prompt I type "telnet " then it seems as if it connects but I don't get the login information

If you already checked your DNS stuff also check the sizes of the "/etc/utmp" and "/etc/wtmp" files maybe they are corrupt or too huge.

There may be threads on how to clear them and the implications thereof.

[David Wilkins]

I can telnet from other Unix servers to the one in question. It will telnet to itself.

Both Hostname and IP address respond in the same way.

[Navin Bhat_2]

Is this fixed yet?

[Rita C Workman]

So let's see if I read this right...

You can telnet from other UNIX boxes ok to this box; and you telnet to the box itself (from itself).

Obviously telnet is working.

But you can't telnet from Windows2000....is there anything blocking telnet, like maybe an IP range is excluded/denied in inetd.sec ?
Another thing, make sure the IP of the PC trying to connect is referenced either in the /etc/host file or via DNS, that way you don't have to wait for a login prompt...
Are enough tty session ? [Had to ask the obvious..]
But since it's starting from a PC....
... maybe PC there is something configured wrong on the PC.
...Remember, PC's will always read the PC host file first ! It doesn't matter what else is defined...if a host file exists it stops there first. If there is an incorrect entry in that file..it chokes resolution. Hence, you ain't a goin anywhere's son !
So you could be checking nslookup on other boxes and getting good resolve, but what about the PC itself.....

Rgrds,
Rita

[David Wilkins]

It is still not working.

It is a very tricky thing to explain...

Telnet will always work from a PC (W2K) after one or two attempts.

I can resolve the server name with nslookup without any problem.

This does not just occur on one PC it is happening on several.

I have tried it with and with out a manual entry in my host file.

[Navin Bhat_2]

what about etherreal trace? did you clear out the utmp/wtmp files?

[Mel Burslan]

Are there any PCs that you know of, which does not have this problem at all, i.e., anytime that you run command

telnet hostname

it gives you the login prompt right away ?

The reason I am asking with almost daily patches going into the windows lately, thanks to the new worms coming out of the woodwork everyday, anything on the windows end is possible. Because while trying to fight the fire, micro$oft programmers do not pay attention to minor things like "what happens to telnet application if I do this change ?" At the end, who needs telnet, right ? Why should one even consider using a *nix system while there is a much better alternative called windows-XP NOT! ? Right ? Even Gartner Group provided proof that Windows is better and cheaper than running Linux (which I am still laughing with the opposite end of my body everytime I think about it by the way)

My suggestion is to compare the service pack levels of a "good" PC and "bad" PC. I do not think this has anything to do with the DNS server or the unix host. Just for the heck of it, if you have a personal windows workstation (like a laptop or a small desktop at home that you can carry for one day) which is not blessed by the forced company updates, I would bring such a workstation and try telneting from that one.

I don't know. I can not think any other possibility.

[David Wilkins]

Quote: what about etherreal trace? did you clear out the utmp/wtmp files? - end quote

I am not familiar with ethereal trace. I do not have a wtmp file and the utmp is only 5k.

The problem I'm having now is it is working flawlessly. It will probably act up again tomorrow but right now I can't trouble shoot it when it is working.

I will try to bring in a "less patched" PC and see if that helps and get back with you tomorrow

Thanks for all of the input

[Bill Hassell]

Ethereal is a free program that formats LAN activity logs. On a PC with a copy of WinPcap, you can trace the actual LAN traffic just for this telnet connection. Get a copy from: http://www.ethereal.com/ and http://winpcap.polito.it/ Ethereal can filter all the traffic on the LAN to just the server or the PC with a problem.

Note that tyhe recommendation about DNS refers to the incoming IP address, not the server's. If your PC's IP address cannot be found by the server, then you'll see a delay. Verify this by adding your problem PC's address into /etc/hosts and edit nsswitch.conf to look on hosts first, then DNS.