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Cisco Bug: CSCur52810 - Low FCIP performance when running NX-OS releases 6.2(5) to 6.2(9c)

Last Modified

Jul 27, 2017

Products (1)

  • Cisco MDS 9000 Series Multilayer Switches

Known Affected Releases

6.2(5)

Description (partial)

Symptom:FCIP tunnels don't fully utilise the available TCP window size. This leads to underperforming FCIP tunnels that never achieve their configured bandwidth on higher latency links.When TCP send queue hits 2MB threshold, the FCIP tunnel is exerting flow control back to the FC ports utilizing the tunnel. This leads to Rx B2B credit depletion. You can see the current size of the send queue via the following command:

<pre>
show ips stats tcp interface gige<x/y>

   Local  Address        Remote Address        State      Send-Q   Recv-Q
    1.1.1.1:65525     2.2.2.2:3225          ESTABLISH  2558928  0
</pre>

Conditions:This issue applies when:

 - NX-OS versions from 6.2(5) to 6.2(9c) inclusive, and
 - the platform is an MDS 9500 or MDS 9222i, and
 - latency on FCIP tunnel is high enough that a TCP window size greater than 2 MB is required
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