Yes The firewall does not involve the specific implementation and mode selection of GRE protocol, because GRE belongs to the network layer protocol, and the firewall mainly focuses on the security policies and filtering rules at the transport layer and above. However, if you refer to the configuration on the firewall to filter and manage GRE traffic, you can adopt mixed mode. Mixed mode refers to the combination of access control list (ACL) and state detection to control and review traffic. By configuring appropriate rules, the firewall can allow or reject packets transmitted through GRE tunnel according to the source address, destination address, port number and other information.