The firewall principle of the cellular router has a series of hardware and software components between different network security domains. Through monitoring and restriction, we can shield the private information, structure and operation status externally as much as possible, and selectively accept external access.
The firewall comes from the field of architectural design and refers to a wall used as a divider to slow or protect other parts from fire when one part catches fire. In a computer network, a firewall is a combination of one or more systems used to set security policies between two or more networks. The firewall serves to isolate abnormal access and allows only steady traffic to pass, thus protecting the security of home and enterprise internal network information.
Linux firewalls usually consist of two parts, iptables and netfilter. iptables is a command-line tool for Linux management firewall rules and in userspace. Netfilter performs message filtering and is in the Linux kernel space. Sometimes iptables is collectively referred to the Linux firewall.
Iptables is used to set, maintain, and check firewall IP message filtering rules and network address translation rules for the Linux kernel.
Iptables is a message status monitoring firewall, which means that the firewall stores information about each connection and can associate each message with the link it belongs to.