Slow performance using ExtremeZ-IP with 3Com 4200 series switches

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Performance when using 3com series 4200 switches in conjunction with ExtremeZ-IP is several times slower than expected.

Steps to Reproduce:

Install ExtremeZ-IP on a server where the clients are connecting thru a 3Com series 4200 switch set to its default settings.


3Com series 4200 switches come preconfigured with a Quality of Service setting (QoS) that conflicts with ExtremeZ-IP’s TCP/IP window size. The 3Com switch does not work efficiently with data protocols using window sizes greater than 18k bytes. ExtremeZ-IP uses a maximum window size of 64k bytes in order to achieve the maximum file transfer speed.

Please refer to the 3Com knowledgebase article with Solution ID 3KB16151. (You must sign in to access the knowledgebase article)

For information on other network issues that could be affecting ExtremeZ-IP performance, please refer to Group Logic’s knowledge base article, “Why is one computer much slower than all the others?” This article is referenced in the “Related articles” section at the bottom of this page.


No workaround is recommended. Please refer to the ‘Cause’ and ‘Fix’ sections within this article.


Disable the QoS setting on the 3Com switch. To configure the QoS manually you will need to run the 3NS ‘Prioritize Traffic’ Wizard. See 3Com knowledgebase article with Solution ID 2.0.106697707.3904730 for more information.