Stateful Firewall and Stateless Firewall

Stateful Firewall:
- Stateful firewall is a type of network layer firewall that keeps track of the state of network connections.
- It maintains a table of active connections known as a state table or state table cache.
- The state table contains information about each connection, such as source and destination IP addresses, port numbers, and connection status (open, closed, or in progress).
- When a packet arrives at the stateful firewall, it is compared against the state table to determine whether it is part of an established connection or a new connection.
- If it is part of an established connection, the firewall allows the packet to pass through.
- If it is a new connection, the firewall checks the packet against its rule set to determine whether it should be allowed or denied.
- Stateful firewalls provide better security and performance compared to stateless firewalls because they can make more intelligent decisions based on the state of connections.

Stateless Firewall:
- Stateless firewall is a type of network layer firewall that does not maintain any information about the state of network connections.
- It makes decisions based solely on the information contained in each individual packet.
- When a packet arrives at a stateless firewall, it is compared against the firewall's rule set to determine whether it should be allowed or denied.
- The firewall does not consider the packet's relationship to any other packets or connections.
- Stateless firewalls are simpler and less resource-intensive compared to stateful firewalls, but they provide less advanced security and do not provide protection against certain types of attacks, such as IP spoofing.

Conclusion:
- The network layer firewall has two sub-categories: stateful firewall and stateless firewall.
- Stateful firewalls maintain a state table of active connections and make decisions based on the state of connections.
- Stateless firewalls make decisions based solely on the information contained in each individual packet and do not maintain any state information.
- Stateful firewalls provide better security and performance, while stateless firewalls are simpler but less secure.