C3750G /Enabling MLS Qos gives performance issues to SUNThin clients

Unanswered Question
Nov 9th, 2009

1. The problem is when a Sun Thin Client and Sun Thin Client Server is connected together on a CAT 3750 with the 'mls qos' command enabled, the Sun Thin Client experiences a screen persistent problem. When the user moves a window across the screen, there is a slow redraw rate. Once "mls qos" command is removed everything is fine.

The thin clients run on 100Mbps and the servers at 1000Mbps across a switch stack of 4 x Cisco 3750.

In troubleshooting this problem, the lab configuration used is just from two devices off a single 3750G switch. The thin client is on Gi1/0/1 and server is on Gi1/0/2.


Have investigated the packets between the server and thin client and have noticed that it is a Sun proprietary protocol based on UDP with packets being 90bytes big. The protocol remains idle unless the user uses the thin client and hence the data flow can be bursty.

Tried applying an ACL, class-map and policy-map and giving the highest priority (af43) to the data but the problem still exists. The packets are being marked correctly as seen by using Wireshark.

Also, to emulate the problem, used iperf to generate UDP packets across two laptops and have noticed that packets begin to be dropped when the bandwidth is set higher than 8Mbps.

The SHOW INTERFACE commands show that there are no packets being dropped however packets are being dropped when performing an iperf test.

I have this problem too.
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Giuseppe Larosa Thu, 11/12/2009 - 09:48

Hello Alphonse,

I think you have enough elements to open a service request on this.

and you have probably already done it.

Hope to help



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