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Old 04-20-2007, 03:29 PM   #1
xafwodahs
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slow ssh response after upgrate to ubuntu 7


Hi, I have a PC which was running Ubuntu 6 and I use PuTTY on a Windows box to ssh telnet into the linux machine. This has worked fine.

Now, I upgraded to Ubuntu 7, and now when I ssh in via Putty, the login takes about 5-6 seconds before I get the password prompt. I have PuTTY configured to specify the username, so I see:

Using username "xyz"

immediately (I don't know if that ssh or putty printing that...)

and then about 5-6 seconds later, I get the password prompt.

This is annoying to me because I routinely open/use/close these telnet sessions on a rapid basis.

How can I log the ssh login process to see what's causing the delay?

Any help would be appreciated.

Note: I did not change my PuTTY configuration, so it must be something related to the new Ubuntu that's causing the delay. Also, if I just type "ssh localhost" from the linuxpc itself, I don't see the delay. Also, from my windows pc, I can ping the linux pc with a turn around time of 0.02 seconds, so the basic connection is fine.
 
Old 04-20-2007, 04:42 PM   #2
acid_kewpie
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only thing that routinely casuses these kinds of delays are reverse dns lookups. can the server find the hostname of the client you're connecting from?
 
Old 04-23-2007, 12:18 PM   #3
xafwodahs
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I installed wireshark on the linux pc and did a capture of this time period.

I see some ssh init, key exchange, diffie-hellman somethingorother, and encryped response packet all within .15 seconds.

Then there is: (time proto info) [time ref is first ssh message]
0.15 DNS "Standard query PTR <windows_ip>.in-addr.arpa"
0.15 DNS "Standard query response, No such name"
0.25 MDNS "Standard query PTR <windows_ip>.in-addr.arpa"
1.26 MDNS "Standard query PTR <windows_ip>.in-addr.arpa"
3.26 MDNS "Standard query PTR <windows_ip>.in-addr.arpa"
5.15 SSHv2 Encrypted response packet

I'm not terribly familiar with reverse DNS - is that what this is? It seems after the first DNS failed, then it tried multicast DNS whatever that is - apparently with no response.

What would cause this and how to do fix it?

Thanks.
 
Old 04-23-2007, 12:23 PM   #4
nx5000
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The server tries to get the name out of the IP (DNS ptr).

You should try to reconfigure the ftp server so that it doesn't do this anymore.
 
Old 04-23-2007, 03:34 PM   #5
acid_kewpie
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he shoots... he scores! right so either look at setting up a local dns server (very very easy with dnsmasq), add details to /etc/hosts on the server machine so they know who the client is, or set UseDNS=NO in your sshd_config file
 
Old 04-24-2007, 06:20 AM   #6
nx5000
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Quote:
Originally Posted by acid_kewpie
he shoots... he scores!
This one was easy, you won't get a free beer for this
 
Old 04-24-2007, 01:45 PM   #7
xafwodahs
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"UseDNS no" worked fine. Thx much!
 
  


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