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.

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?

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.

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.

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

This one was easy, you won't get a free beer for this ;)

"UseDNS no" worked fine. Thx much!