CVAD: Slow file transfers from VDA to client drive on a local network, on 1912 CU5 VDA

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Article ID: CTX463701

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Updated On:

Description

Clients experiencing slow file transfers while connected to the internal networks or on LAN . 

The maximum file transfer speed would be at 350KB/s on each occasion when user attempts to copy the file from VDA to a Local drive on Client machine via Client Drive Mapping

Resolution

If viewing MTU size as 1410 which means TCP MSS should be 1370 based on the formula in the article (TCP MSS = MTU (1410) – IP+TCP Header (40)).

 
  1. On the device, apply these registry settings:
HKEY_LOCAL_MACHINE\SOFTWARE\Citrix\ICA Client\Engine\Configuration\Advanced\Modules\TCP/IP "OutBufLength"="1370"
HKEY_LOCAL_MACHINE\SOFTWARE\Citrix\ICA Client\Engine\Configuration\Advanced\Modules\TCP/IP "OutBufCountClient2"= Number of OutBufs

HKEY_LOCAL_MACHINE\SOFTWARE\Citrix\ICA Client\Engine\Configuration\Advanced\Modules\TCP/IP "OutBufCountHost2"= Number of OutBufs

The value of "Number of OutBufs" above should be calculated as follows:
Number of Buffers = TCP Receive Window/1370 where:
  • TCP Receive Window = Bandwidth (kbps) / 8 X Latency in ms
  • Example, if the bandwidth over IPSEC tunnel is 50Mbps, then:
50Mbps = 50x1024 = 51200 Kbps
  • TCP Receive window = 51200 (divided by) 8 (multiplied by) 20 (latency in ms), ie 128,000
  • In this example, Number of Buffers = 128000/1370, that is  93.4 which when rounded up will be 94.
Note: If the registry key can't be found in the location above, an alternate place to look is: HKEY_LOCAL_MACHINE\Software\wow6432node\citrix\ICA Client\Engine\Configuration\Advanced\Modules\TCP/IP

Problem Cause

TCP MSS configuration which needs a tweak based on the network bandwidth
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