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Nur
Staff
Nur
Staff
October 27, 2025

Technical Tip: How to troubleshoot when Log Forwarding sending Jumbo packet to Destination

  • October 27, 2025
  • 0 replies
  • 387 views
Description

This article describes how to troubleshoot when Log Forwarding sends a Jumbo packet to the Destination: FortiGate -> FortiAnalyzer (Log Forward) -> FortiGate -> Destination.
Scope FortiAnalyzer, FortiGate.
Solution Screenshot 2025-10-26 090051.png

 

  1. X.X.1.7: FortiAnalyzer IP.
  2. X.X.8.35: Destination IP.
  3. Based on the packet capture, the FortiAnalyzer is sending a Jumbo Frame to the destination.
  4. When the traffic sends packets larger than the Maximum Transmission Unit (1500bytes), the packet needs to be fragmented the packet into small pieces.
  5. The packet does not fragment cause the High Bandwidth.

 

Screenshot 2025-10-26 091205.png

 

Refer to the troubleshooting below to fix the fragment issue.

 

FortiGate (Sender/Receiver) :

 

Configure the default MTU size at Policy FortiGate:
 
config firewall policy
    edit XXXXX
tcp-mss-sender : XXXXX
tcp-mss-receiver : XXXX
end

 

FortiAnalyzer :

Turn off segmentation-offload:

 

diagnose system interface segmentation-offload port <action> // off||on

 

 
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