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Operating System - Tru64 Unix
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Slooow... SSH2 - X11 forwading (Tunneling)

Ed Notari
Occasional Contributor

Slooow... SSH2 - X11 forwading (Tunneling)

This message has been previously sent to an Alpha-Managers Listserv.

Problem in a nutshell;
We are seeing performance issues as we are trying to implement SSH2 and X11 forwarding (tunneling) for X-Apps to the desktop. Specifically, "jerky" or slowed performance in NEDIT and some lag times in other x-apps.

The specs;
ES40 2x667MHz, 1GB RAM, Tru64 v5.1A, fully patched, latest Tru64 SSH2, 100Mb full to switch, VLAN2.
_DESKTOP_ Intelium 2.4GHz, 1GB RAM, W2KPro, PuTTY, ReflectionX, 10Mb full to switch, VLAN2.

The SSH2 configuration is mostly default.

Is this type of performance lag normal?
It certainly hasn't happened when running ReflectionX via telnet.

It doesn't seem to be caused be unusual packet sizes traversing blades in the switch. I connected directly to a secondary ethernet connection on the ES40 using a PC164LX Alpha system (same OS) and saw similar performance issues from alpha to alpha.

Is there a way to test for or mitigate this problem?
If any more info is needed please advise and I will provide it.

Ed Notari
Ralf Puchner
Honored Contributor

Re: Slooow... SSH2 - X11 forwading (Tunneling)

1. try to use the command truss or trace (must be installed seperatly) within the ssh command execution. Have a look to the socket open calls and check if TCP_NODELAY was set.


create a trace of the communication and check the time of acknoledge from the receiver side. Check for gabs - maybe an indicator for high watermarks or timeouts.

2. Sending data from 100MBit to 10MBit leads to an performance issue on switch side. Test with 10MBit on server and client side. If problem is gone replace switch by another model/vendor.
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