# packet filter

> software which inspects packets transferred between computers and blocks or allows them

**Wikidata**: [Q831660](https://www.wikidata.org/wiki/Q831660)  
**Source**: https://4ort.xyz/entity/packet-filter

## Summary
A packet filter is software that inspects data packets transferred between computers and either blocks or allows them based on rules. It is a type of firewall — a network security system that monitors and controls incoming and outgoing network traffic according to predetermined security rules.

## Key Facts
- Packet filter is software that inspects packets transferred between computers and blocks or allows them (Wikidata description).  
- Packet filter is classified as instance_of: software category.  
- Packet filter is subclass_of: firewall (a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules).  
- Alias: "Netzwerkfilter".  
- Related technology: Berkeley packet filter — an interface to data link layers on a Unix-like system; inception: 1992.  
- Wikidata/use property identifier: Q1885572.  
- Sitelink_count (Wikidata): 4; Wikipedia language pages available in German (de), Hungarian (hu), Indonesian (id), and Dutch (nl).  
- Google Knowledge Graph ID: /g/121hf7xt.

## FAQs
### Q: What does a packet filter do?
A: A packet filter inspects packets transferred between computers and either blocks or allows them based on inspection rules. It enforces access decisions at the packet level as part of network traffic control.

### Q: How is a packet filter related to a firewall?
A: A packet filter is a subclass of a firewall. A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules; packet filters implement that function at the packet inspection level.

### Q: Is the Berkeley packet filter the same as a packet filter?
A: The Berkeley packet filter is a related technology. It is an interface to data link layers on Unix-like systems (inception 1992) and is commonly used for low-level packet capture and filtering, but it is described as a related interface rather than the general packet filter class itself.

## Why It Matters
Packet filters are a fundamental mechanism for enforcing network security policies at the packet level. By inspecting individual packets and making allow-or-block decisions, packet filters control traffic flow between hosts and networks and implement basic access controls that underpin many higher-level security measures. As a subclass of firewalls, packet filters provide a lightweight, rule-driven approach to preventing unauthorized traffic, detecting simple anomalies, and segregating network segments. They also interface with low-level packet capture and filtering technologies — for example, the Berkeley packet filter (1992) provides an interface to data link layers on Unix-like systems — which enables software and tools to observe and act on network packets directly. Because packet filters are software components, they are adaptable and can be embedded in routers, host-based firewalls, and network appliances to meet specific security requirements.

## Notable For
- Being the software-level mechanism that inspects and decides to block or allow individual network packets.  
- Classification as a subclass of firewall, tying it directly to the broader field of network traffic control and security.  
- Explicit alias in German: "Netzwerkfilter."  
- Relation to the Berkeley packet filter, a 1992 interface for data link layer access on Unix-like systems.

## Body
### Definition
- Packet filter: software which inspects packets transferred between computers and blocks or allows them.  
- The definition is recorded as the entity's description in Wikidata.

### Classification and Parentage
- Instance of: software category.  
- Subclass of: firewall.  
- Parent class "firewall" is defined as a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules.

### Identifiers and Links
- Wikidata/use property identifier: Q1885572.  
- Google Knowledge Graph ID: /g/121hf7xt.  
- Sitelink_count on Wikidata: 4.  
- Wikipedia language pages listed: de (German), hu (Hungarian), id (Indonesian), nl (Dutch).

### Aliases and Naming
- Known alias: Netzwerkfilter.

### Related Technologies
- Berkeley packet filter (related Thing): described as an interface to data link layers on Unix-like systems.  
- Berkeley packet filter inception year: 1992 (reference available: https://www.tcpdump.org/papers/bpf-usenix93.pdf).

### Scope and Role
- Operates at the packet level to make allow/block decisions for network traffic.  
- Functions as a software component within the broader firewall class of network security systems.