The Log shows "Received packet retransmission. Drop duplicate packet

The Log shows "Received packet retransmission. Drop duplicate packet.

The SonicWall received two identical packets and dropped one of them.

Resolution for SonicOS 7.X

This release includes significant user interface changes and many new features that are different from the SonicOS 6.5 and earlier firmware. The below resolution is for customers using SonicOS 7.X firmware.

This log message is related to either TCP retransmission issues (for protocols such as HTTP) or the VPN configuration. It can be a Site-to-Site VPN, Client-to-Site VPN, L2TP or PPTP setup.

The following is a check list for troubleshooting Packet Retransmission messages:

1. Check MTU settings- Navigate to Network | System | Interfaces | WAN | Advanced | Interface MTU.
   
   NOTE:  It is recommended to check the 'Fragment outbound packets larger than WAN MTU' if the MTU is set below the default of 1500. Use the 'Update' button to process the changes entered.
2. Fragment Packet Handling should be enabled.
3. Pre-shared Key mismatch should be checked.
4. Check the gateway IP address and firewall name or serial number specified in the VPN policy on each end of the tunnel.
5. Lower the encryption settings.
6. Check the upstream device configuration.
7. Check for the NAT Traversal option.
8. On the computer where GVC is installed, make sure the NAT Traversal option is disabled under Connection Properties --> Peers --> Edit --> NAT - Traversal.

Resolution for SonicOS 6.5

This release includes significant user interface changes and many new features that are different from the SonicOS 6.2 and earlier firmware. The below resolution is for customers using SonicOS 6.5 firmware.

This log message is related to either TCP retransmission issues (for protocols such as HTTP) or the VPN configuration. It can be a Site-to-Site VPN, Client-to-Site VPN, L2TP or PPTP setup.

The following is a check list for troubleshooting Packet Retransmission messages:

1. Check MTU settings- Navigate to Manage | Network | Interfaces > WAN | Advanced | Interface MTU.
   
   NOTE: It is recommended to check the 'Fragment outbound packets larger than WAN MTU' if the MTU is set below the default of 1500. Use the 'Update' button to process the changes entered.
2. Fragment Packet Handling should be enabled.
3. Pre-shared Key mismatch should be checked.
4. Check the gateway IP address and firewall name or serial number specified in the VPN policy on each end of the tunnel.
5. Lower the encryption settings.
6. Check the upstream device configuration.
7. Check for the NAT Traversal option.
8. On the computer where GVC is installed, make sure the NAT Traversal option is disabled under Connection Properties --> Peers --> Edit --> NAT - Traversal.