TCP URG Packets dropped as " Invalid TCP flag "
05/31/2022 0 People found this article helpful 16,480 Views
When a device is sending TCP packets with URG flag firewall is dropping the packet as Invalid TCP flag. This is causing interruptions in TCP communication.
Source is sending TCP packet with URG pointer set and firewall is dropping this packet as " Invalid TCP Flag"
Below Resolution is applicable for devices using SonicOS 7.x firmwares :
NOTE: This is caused as the source is sending TCP packet SYN , ACK with URG flag and firewall is configured to drop URG packets.
- Determine the zones from where this traffic is coming in from
- Find the access rule that this traffic is using to reach the destination device
- Navigate to Policies tab |Rules and Policies . Click on configure for the access rule used for this traffic
- Click on Optional settings of the access rule and enable Allow TCP Urgent Packets option
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