Sonicwall - NSA 2400 TCP Handshake Violation

Posted on 2013-11-04
Last Modified: 2013-11-08
Good morning,
I have a Sonciwall NSA 2400 with multiple Sub Interfaces/VLAN's.  One of these VLAN's hosts an WIN2K8 RDS Server.  When users logon and try to access the internet, loads of the below errors get logged on the Sonicwall.  The users web connections never resolve properly.  

We have tried.

 1.  Turning off TCP timeout.
 2.  Disable Content Filtering

Any ideas?

1      11/04/2013 11:11:21.384      Debug      Network      TCP packet received on non-existent/closed connection; TCP packet dropped, 51782, X2:V201, 443, X1      TCP Flag(s): ACK              
2      11/04/2013 11:10:21.192      Debug      Network      TCP packet received on non-existent/closed connection; TCP packet dropped, 51746, X2:V201, 443, X1      TCP Flag(s): ACK              
3      11/04/2013 11:08:51.704      Debug      Network Access      Broadcast packet dropped, 0, X2:V201, 20584      Protocol:137              
4      11/04/2013 11:05:56.128      Notice      Network Access      TCP handshake violation detected; TCP connection dropped, 51604, X2:V201, 8059, X1      Handshake Timeout              
5      11/04/2013 11:05:43.880      Debug      Network Access      Broadcast packet dropped, 0, X2:V201, 20584      Protocol:137              
6      11/04/2013 11:04:51.160      Notice      Network Access      TCP handshake violation detected; TCP connection dropped, 51563, X2:V201, 445, X1      Handshake Timeout              
7      11/04/2013 11:04:39.544      Debug      Network      TCP packet received on non-existent/closed connection; TCP packet dropped, 51316, X2:V201, 80, X1      TCP Flag(s): ACK              
8      11/04/2013 11:03:01.112      Notice      Network Access      TCP handshake violation detected; TCP connection dropped, 51499, X2:V201, 8059, X1      Handshake Timeout              
9      11/04/2013 11:02:59.144      Debug      Network      TCP packet received on non-existent/closed connection; TCP packet dropped, 51449, X2:V201, 80, X1      TCP Flag(s): ACK
Question by:GeminiTechnology
  • 2
LVL 25

Accepted Solution

Diverse IT earned 500 total points
ID: 39621678
Hi GeminiTechnology,

What is the SonicOS firmware version? (you most likely need to upgrade your firmware)
Have you performed any hardening on the security appliance?
What type of WAN connection is being used?

This Log message is displayed when the SonicWALL firewall receives a TCP packet after a particular connection was closed.

This is a generic error message as there are a number of root causes that can create this error. For example: A packet was delayed in transition for some reason and reaches the SonicWALL after the connection was closed. The SonicWALL Firewall drops the packet and logs the message.

Login to the SonicWALL and go to Firewall Settings > Flood Protection then match the following settings:
Under TCP Settings
• Enforce strict TCP compliance with RFC 793 and RFC 1122: Uncheck
        • Enable TCP handshake enforcement: Uncheck
• Enable TCP checksum enforcement: Uncheck
• Enable TCP handshake timeout: Uncheck
Layer 3 SYN Flood Protection - SYN Proxy
• SYN Flood Protection Mode: select Watch and report possible SYN floods
Then re-test with new connections (terminating the old ones by closing the browsers).

If that still fails to resolve, follow below:
Increase the Inactivity timeout of the rules on the SonicWALL.
VPN tunnels: You may need to increase activity timeout on the LAN to VPN as well as the VPN to LAN rule to avoid timeout conditions.
Make sure the upstream device, source and destination computers connecting to each other do not have latency.

Let me know how it goes and please answer the above questions in the interim.

Author Closing Comment

ID: 39633304
Thank you!
LVL 25

Expert Comment

by:Diverse IT
ID: 39634254
You're welcome! Glad I could help...thanks for the points!

Featured Post

Save on storage to protect fatherhood memories

You're the dad who has everything. This Father's Day, make sure your family memories are protected. My Passport Ultra has automatic backup and password protection to keep your cherished photos and videos safe. With up to 3TB, you have plenty of room to hold the adventures ahead.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

If you're not part of the solution, you're part of the problem.   Tips on how to secure IoT devices, even the dumbest ones, so they can't be used as part of a DDoS botnet.  Use PRTG Network Monitor as one of the building blocks, to detect unusual…
ADCs have gained traction within the last decade, largely due to increased demand for legacy load balancing appliances to handle more advanced application delivery requirements and improve application performance.
Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.
This video gives you a great overview about bandwidth monitoring with SNMP and WMI with our network monitoring solution PRTG Network Monitor ( If you're looking for how to monitor bandwidth using netflow or packet s…

919 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

18 Experts available now in Live!

Get 1:1 Help Now