Wireless Access

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Occasional Contributor II

FTP SYN packet being dropped - FTP delays

We're experiencing a puzzling situation where wireless Dell thin clients are taking an extended time to boot due to delays in interacting with the FTP server.  Each time a thin client boots, it retrieves 6 files from an onsite FTP server.  This process takes <2 seconds on the wired network but closer to 25 seconds on wireless (both clients on the same VLAN / IP space).  A packet capture at the AP reveals that each time the client starts the 3-way handshake, it sends an FTP SYN packet to the server that isn't being ack'd.  The client re-transmits the FTP SYN 3 seconds later and receives the ACK immediately this time, then goes about it's business of completing the FTP transaction.  This process repeats 6 times (6 files to be retrieved) and each time the initial FTP SYN packet is lost and each time the FTP SYN retrans 3 seconds later is ack's immediately.  These 6 @ 3-second delays between retransmissions add up to 18 seconds of additional time (plus overhead) it takes for a wireless thin client to boot.  But my concern isn't so much the 18 seconds as it is the thought that the loss of the first FTP SYN packet every time is a symptom of a bigger underlying problem.  This is a 7200 master/local environment with AP-225's running 6.4.4.16.  Any thoughts?

Guru Elite

Re: FTP SYN packet being dropped - FTP delays

You should take a pcap at the controller's interface and/or at the FTP server's interface at the same time to understand where the traffic is being dropped.

 

You could take an unencrypted pcap of the client's traffic by doing this http://community.arubanetworks.com/t5/Controller-Based-WLANs/HOW-TO-DO-DATAPATH-PACKET-CAPTURE-FOR-WIRELESS-CLIENT-FROM/ta-p/179940

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Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.
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Occasional Contributor II

Re: FTP SYN packet being dropped - FTP delays

The next step is to take a capture at the firewall and FTP server interfaces, I just thought maybe this is something that others had experienced as we're fairly certain it's a "wireless" issue as the problem does not present with the same client plugged into a wired port on the same VLAN.

 

Guru Elite

Re: FTP SYN packet being dropped - FTP delays

I will let others chime in.  My approach is to understand where the bottleneck could possibly be.  Maybe others have an immediate solution.

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Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.
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