Technical Tip: SOCKS5 'Command Not Supported (7)' error when connecting to FortiProxy

The error Command not supported (7) occurs when a SOCKS5 client attempts to establish a SOCKS5 connection through FortiProxy by using a command that is not supported, such as Bind or UDP ASSOCIATE.

Results from a packet capture when connecting through FortiProxy using SOCKS5

Frame 33: 76 bytes on wire (608 bits), 76 bytes captured (608 bits)
Ethernet II, Src: Fortinet_09:00:02 (00:09:0f:09:00:02), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 192.168.10.10, Dst: 10.100.11.12
Transmission Control Protocol, Src Port: 1080, Dst Port: 59532, Seq: 3, Ack: 14, Len: 10
Socks Protocol
Version: 5
Results(V5): Command not supported (7)
Reserved: 0
Address Type: IPv4 (1)
Remote Address: 0.0.0.0
Port: 0

Ensure that SOCKS5 clients are configured to use only the CONNECT command when communicating through FortiProxy.