Re: ssh communication issue
Larry Irwin wrote:
Our ssh connections work fine on all our servers when we connect via the
local network.
But, when we ssh from the internet, there are long pauses where i/o is
not displayed/echoed to the screen on our Debian servers.
We experience 10 to 30 second pauses after a screen or 2 of display on
Debian Etch kernel 2.6.12, SSH-2.0-OpenSSH_4.2p1 Debian-5.
We have same issue, with slightly shorter pauses, on a Debain Sarge
kernel 2.4.18, OpenSSH_3.4p1 Debian 1:3.4p1-1.woody.3.
We do not experience the problem on a SCO OS5 3.2v5.0.5 kernel,
OpenSSH_2.2.0p1
Does anyone know what might me contributing to the screen IO issue?
Cheers,
Larry
Nate Duehr wrote:
You're not very clear about which portion of the session is slow.
The interactive session after login.
Individual characters echoing back from the remote end after you're at a
shell? The initial connection process?
All i/o is either normal (i.e. almost immediate) or frozen for a while.
Look for...
A slow network. (Latency across the Internet is not great for interactive
keyboard sessions, in many cases.)
A slow DNS lookup or lack of /etc/hosts entries. (During the connection
process, SSH looks up your remote machine's name via reverse DNS lookups.
Are you coming from machines that don't have proper reverse DNS entries on
the new Debian machines, whereas the old SCO machine has a proper reverse
DNS entry?)
None of the machines have proper entries for reverse DNS lookups. We will
never know what our remote IP will be when accessing our servers from remote
locations. For testing purposes, I am ssh'ing from the Etch box 3 times to
the same remote server, then ssh'ing back to the 3 aforementioned servers
from the remote server. -- Of note is the following: On the ssh session back
to the SCO box I can telnet over the LAN from the SCO box to the Etch box
and I never have any pauses. So, if I ssh to the SCO box and then initiate
local connections, I'm OK... But a direct connection to either of the Debian
boxes intermittently freezes i/o.
A slow machine. (Are all these machines the same speed/quality?)
ssh -v will help you see what portion of the process is slow if it's
during the connection process.
Connecting is not an issue to/from any of them, just the interactive
sessions.
The SCO box is a PII 400MHz 256MB RAM, the Etch box is a PIV 3GHz 1GB RAM
The SCO box is the oldest and slowest.
If it's after you're connected, see what the ping times between your
server and your client are. That's the biggest factor in how
"interactive" your keyboard will feel.
Remote client (Sarge) to server (Etch):
64 bytes from xxx.xxx.xxx.xxx: icmp_seq=0 ttl=241 time=55.6 ms
64 bytes from xxx.xxx.xxx.xxx: icmp_seq=1 ttl=241 time=56.4 ms
64 bytes from xxx.xxx.xxx.xxx: icmp_seq=2 ttl=241 time=56.5 ms
64 bytes from xxx.xxx.xxx.xxx: icmp_seq=3 ttl=241 time=55.7 ms
Server (Etch) to remote client (Sarge):
64 bytes from xxx.xxx.xxx.xxx: icmp_seq=1 ttl=37 time=55.3 ms
64 bytes from xxx.xxx.xxx.xxx: icmp_seq=2 ttl=37 time=56.1 ms
64 bytes from xxx.xxx.xxx.xxx: icmp_seq=3 ttl=37 time=60.1 ms
64 bytes from xxx.xxx.xxx.xxx: icmp_seq=4 ttl=37 time=56.3 ms
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