SPI Firewall Explained

An SPI firewall is a more powerful version of the network firewall that exists in your router. Its job is to ensure that incoming data packets are legitimate. It’s a powerful firewall that can prevent malicious data packets and external attacks. Wondering what is SPI firewall and how does it work? Let us explain. 

Firewall Explained

A firewall is a security system that monitors network traffic and allows it to pass or block it. Many data packets and connection requests are exiting and entering your device while you are on it. Programs on your computer can initiate a connection request to an outside network. 

The problem is that there could be malicious programs on your computer that could be trying to communicate with its developer (hacker). A firewall analyzes what traffic entering through the ports and its source address and refers to the set rules to determine if it should be allowed or blocked. For example, as a network administrator, you can block communications to a certain port, and any application requesting to use the port will not be able to communicate. 

This kind of firewall is called a stateless firewall. And why exactly it’s called as such will become clear when we discussed how SPI firewall works. 

What is SPI Firewall?

Stateful Packet Inspection (SPI) is an advanced firewall and a contrast to a stateless firewall. It monitors network traffic for any unwanted traffic just like a stateless firewall but does so in a comprehensive way. 

An SPI firewall authenticates data packets by looking at certain information, such as connection state, source, and destination address. It determines whether the data packets belong to an active session or not. SPI firewall is capable of keeping track of both TCP and UDP network connections. 

TCP (Transmission Control Protocol) is a connection-oriented protocol that establishes a connection and waits for an acknowledgment after every data packet transmission before proceeding to the next data packet. In contrast, UDP is a connectionless protocol that prioritizes speed over accuracy and does not care for acknowledgment. 

SPI firewall can track both connection types. For TCP, it keeps checks if the data packets belong to an active session. And it can determine the same for UDP based on the configured session length. 

What are the Advantages of SPI Firewall?

Stateless firewall are only good for a basic level of network security. Enterprises will benefit from SPI because it can prevent external attacks like DDoS. It is aware of the connection requests and does not discard the data even if they belong to a legitimate application like a stateless fireless. 

• SPI can store information about outbound and inbound connections. 
• It can examine data packets to see if they belong to an active session. 
• It can detect external attacks by referring to known attacks, such as DoS (Denial of Service) and Ping of Death. 
• The firewall can track both TCP and UDP connections. 
• SPI can track if a data packet belongs to a series of data packets. 
• It can detect if external traffic is in response to a request from you. 

How to Enable SPI in Router

SPI is an advanced feature that is not present in all routers. More robust home routers and enterprise routers have the option. Different routers have different user interfaces; hence no one tutorial can work for all router models. However, the core approach remains the same. 

1. Open the router’s settings. The admin panel’s address and your username and password will be on the router’s back or is manual. 
2. Locate firewall settings in the security menu. 
3. The option to turn on the SPI firewall should be there if your router supports it.

It’s easier to refer to the product manual to confirm if the router features an SPI firewall. Newer router models would have the option to enable/disable IPv4 and IPv6 firewall protection. 

Does a VPN Interfere with SPI Firewall?

A VPN does not interfere with the function of an SPI firewall. A VPN connects you to the internet through a VPN server, while an SPI firewall simply acts as a cop for your internet traffic. 

When you install iProVPN, it makes an entry into the firewall with the TAP network adapter to allow access to the internet. So, when you connect to a VPN server, the SPI firewall will not block its traffic. 

Final Words

With all that said, SPI does have a speed penalty. It is more demanding because it has to check and authenticate each data packet. It is most useful for enterprises where security plays a more important role in preventing external attacks and malware-initiated requests.