Packet Filter (PF) is a renown firewall application that is maintained upstream by the security-driven OpenBSD project. It is more accurately expressed as a packet filtering tool, hence the name, and it is known for its simple syntax, user-friendliness, and extensive features. PF is a stateful firewall by default, storing information about connections in a state table that can be accessed for analytical purposes. PF is part of the FreeBSD base system and is supported by a strong community of developers. Although there are differences between the FreeBSD and OpenBSD versions of PF related to kernel architectures, in general their syntax is similar. Depending on their complexity, common rulesets can be modified to work on either distribution with relatively little effort.
This rule applies scrubbing to all incoming traffic. You include the fragment reassemble option that prevents fragments from entering the system. Instead they are cached in memory until they are reassembled into complete packets, which means your filter rules will only have to contend with uniform packets. You also include the max-mss 1440 option, which represents the maximum segment size of reassembled TCP packets, also known as the payload. You specify a value of 1440 bytes, which strikes a balance between size and performance, leaving plenty of room for the headers.
Ans: Network firewall protects your network from unauthorized access. It filters traffic based on the configuration set by the firewall administrator. The firewall basically performs two functions, block and permit traffic based on configuration.
Ans: Firewall filters network traffic based on the configuration set by the firewall administrator. It can permit or block any port number, web application, and network-layer protocols based on configuration.
Proxy firewall combines stateful inspection technology to enable deep packet inspection. Here, the firewall act as a proxy; a client makes a connection with the firewall, and then the firewall makes a separate connection to the server on behalf of the client.
Ans: In simple words, a packet-filtering firewall filters traffic based on packet attributes such as source and destination addresses, source and destination port numbers, and protocol types.
Ans: Circuit Level Gateway is considered more secure because Packet-filtering solutions filter traffic based on packet attributes, as discussed in the previous question. Circuit Level Gateway filters are based on the communication pattern of TCP/IP packets. Packet-filtering solutions open the system to denial-of-service (DoS) attacks (buffer overflow exploits in \"allowed\" applications on target machines, connections exhaustion). However, Circuit Level Gateway filters are also not able to protect the system from DoS attacks completely.
Ans: Stateful inspection is the most effective way to secure a network. It combines the features of the packet filtering firewall, Circuit Level Gateway, and Application Level gateway.
The term firewall originally referred to a wall intended to confine a fire within a line of adjacent buildings. Later uses refer to similar structures, such as the metal sheet separating the engine compartment of a vehicle or aircraft from the passenger compartment. The term was applied in the late 1980s to network technology that emerged when the Internet was fairly new in terms of its global use and connectivity. The predecessors to firewalls for network security were routers used in the late 1980s. Because they already segregated networks, routers could apply filtering to packets crossing them.
The first reported type of network firewall is called a packet filter, which inspects packets transferred between computers. The firewall maintains an access control list which dictates what packets will be looked at and what action should be applied, if any, with the default action set to silent discard. Three basic actions regarding the packet consist of a silent discard, discard with Internet Control Message Protocol or TCP reset response to the sender, and forward to the next hop. Packets may be filtered by source and destination IP addresses, protocol, source and destination ports. The bulk of Internet communication in 20th and early 21st century used either Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) in conjunction with well-known ports, enabling firewalls of that era to distinguish between specific types of traffic such as web browsing, remote printing, email transmission, and file transfers.
The first paper published on firewall technology was in 1987 when engineers from Digital Equipment Corporation (DEC) developed filter systems known as packet filter firewalls. At AT&T Bell Labs, Bill Cheswick and Steve Bellovin continued their research in packet filtering and developed a working model for their own company based on their original first-generation architecture. In 1992, Steven McCanne andVan Jacobson released paper on BSD Packet Filter (BPF) while at Lawrence Berkeley Laboratory.
Endpoint-based application firewalls function by determining whether a process should accept any given connection. Application firewalls filter connections by examining the process ID of data packets against a rule set for the local process involved in the data transmission. Application firewalls accomplish their function by hooking into socket calls to filter the connections between the application layer and the lower layers. Application firewalls that hook into socket calls are also referred to as socket filters.
Teams set up a firewall inline across a network to act as a border between external sources and the guarded system. Admins create so-called choke points at which a firewall inspects all data packets entering and leaving the network. A packet is a piece of data formatted for Internet transfer that contains:
A hardware firewall (or an appliance firewall) is a separate piece of hardware that filters traffic entering and coming out of a network. Unlike a software firewall, these self-contained devices have their own resources and do not consume any CPU or RAM from host devices.
These types of firewalls only analyze surface-level details and do not open the packet to examine its payload. A packet-filtering firewall examines each packet in a vacuum without considering existing traffic streams.
This simplistic firewall type quickly approves or denies traffic without consuming a lot of resources. However, these systems do not inspect packets, so even malware-infected requests get access if there's a proper TCP handshake.
A stateful inspection firewall (or dynamic packet-filtering firewall) monitors incoming and outgoing packets at the network and transport layers. This firewall type combines packet inspection and TCP handshake verification.
Stateful inspection firewalls maintain a table database that tracks all open connections and enables the system to check existing traffic streams. This database stores all key packet-related info, including:
When a new packet arrives, the firewall checks the table of valid connections. Familiar packets go through without further analysis, while the firewall evaluates non-matching traffic according to the pre-set ruleset.
Proxy firewalls operate at the app layer, the highest level of the OSI model. These systems have deep packet inspection (DPI) capabilities that check both payloads and headers of incoming traffic.
A firewall is a type of cybersecurity tool used to filter traffic on a network. Firewalls can separate network nodes from external traffic sources, internal traffic sources, or even specific applications. Firewalls can be software, hardware, or cloud-based, with each type of firewall having unique pros and cons.
Circuit-level gateways are another simplistic firewall type meant to quickly and easily approve or deny traffic without consuming significant computing resources. Circuit-level gateways work by verifying the transmission control protocol (TCP) handshake. This TCP handshake check is designed to ensure that the session the packet is from is legitimate.
While extremely resource-efficient, these firewalls do not check the packet itself. So, if a packet held malware but had the proper TCP handshake, it would easily pass through. Vulnerabilities like this are why circuit-level gateways are not enough to protect your business by themselves.
This firewall type combines packet inspection technology and TCP handshake verification to create a more significant level of protection than either of the two architectures could provide alone.
Hardware firewalls use a physical appliance that acts like a traffic router to intercept data packets and traffic requests before they're connected to the network's servers. Physical appliance-based firewalls like this excel at perimeter security by ensuring malicious traffic from outside the network are intercepted before the company's network endpoints are exposed to risk.
The primary benefit of having cloud-based firewalls is that they are straightforward to scale with your organization. As your needs grow, you can add additional capacity to the cloud server to filter larger traffic loads. Cloud firewalls, like hardware firewalls, excel at perimeter security.
This chapter describes the concepts, tools, and methods for configuring the firewall by using packet filtering. It also provides examples for displaying the firewall settings that enforce network security on a system.
A firewall filters incoming and outgoing network packets, based on packet hea