# ARP cache

> collection of Address Resolution Protocol entries

**Wikidata**: [Q3623683](https://www.wikidata.org/wiki/Q3623683)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/ARP_cache)  
**Source**: https://4ort.xyz/entity/arp-cache

## Summary
An ARP cache is a specialized type of cache that stores a collection of Address Resolution Protocol (ARP) entries. Its primary function is to hold recent mappings between IP addresses and MAC addresses on a local network, avoiding the need for repeated ARP broadcast queries and thereby improving network communication efficiency.

## Key Facts
- **Definition:** A collection of Address Resolution Protocol entries.
- **Classification:** It is a specific **subclass_of** the general **cache** [class].
- **Facet:** It is a **facet_of** the **Address Resolution Protocol**.
- **Aliases:** Known as "Table ARP".
- **Sitelink Count:** Has a **sitelink_count** of **3**.
- **Wikipedia Title:** The Wikipedia article is titled **"ARP cache"**.
- **Wikipedia Languages:** The article exists in **German (de)**, **English (en)**, and **French (fr)**.
- **Wikidata Description:** Described as "collection of Address Resolution Protocol entries".
- **Google Knowledge Graph ID:** Identified by **/g/121x71fn**.

## FAQs
**Q: What is an ARP cache?**
A: An ARP cache is a temporary storage area in a computer's networking stack that holds recent Address Resolution Protocol (ARP) entries. These entries map IP addresses to physical MAC addresses, which is essential for delivering data packets on a local network.

**Q: How does an ARP cache improve network performance?**
A: By storing successful IP-to-MAC address mappings, the ARP cache eliminates the need to broadcast a new ARP request for every packet sent to a recently contacted device. This reduces network broadcast traffic and lowers latency for subsequent communications with that device.

**Q: Is the ARP cache hardware or software?**
A: The ARP cache is a software-managed data structure, typically implemented within the operating system's network stack. It resides in the system's RAM, making it a form of software cache, distinct from hardware caches like CPU cache.

**Q: How long do entries stay in the ARP cache?**
A: Entries remain in the ARP cache for a limited, configurable time period (often a few minutes). This timeout ensures that stale mappings, such as those for devices that have changed IP addresses or left the network, are eventually purged to maintain accuracy.

**Q: What happens if an ARP cache entry is missing or incorrect?**
A: If a needed IP-to-MAC mapping is not found in the cache (a cache miss), the system must broadcast an ARP request to resolve the address. If a cached entry is incorrect (e.g., due to an IP address conflict), it can lead to communication failures until the entry times out and is refreshed.

## Why It Matters
The ARP cache is a critical optimization for local area network (LAN) communication. Without it, every single IP packet destined for a new host would trigger a time-consuming ARP broadcast request, consuming bandwidth and processing power on all devices in the broadcast domain. By caching these resolutions, the ARP cache dramatically reduces this overhead, making network interactions faster and more efficient. It is a fundamental component of the TCP/IP protocol suite's practical implementation, directly impacting the responsiveness and throughput of everyday network activities like web browsing, file sharing, and printer access.

## Notable For
- **Network Efficiency Pioneer:** It was one of the earliest and most fundamental caching mechanisms implemented in network protocols to solve the broadcast storm problem inherent in address resolution.
- **Transparent Operation:** Like all caches, it operates automatically and transparently to applications and users, requiring no configuration for basic functionality.
- **Universal Implementation:** Virtually every device that implements the ARP protocol (computers, routers, printers, IoT devices) includes an ARP cache as a standard feature.
- **Security Relevance:** The ARP cache is a target for ARP spoofing/poisoning attacks, making its management and security a key concern in network defense.
- **Protocol-Specific Design:** It is a prime example of a cache designed for a very specific, narrow purpose within a larger protocol stack, unlike more general-purpose caches like disk or web caches.

## Body

### Definition and Core Function
An ARP cache is a **transparent data store** maintained by a host's network layer. Its sole content is a dynamic table of **Address Resolution Protocol (ARP) entries**. Each entry is a mapping that associates an IPv4 address on the local network segment with the corresponding physical MAC (Media Access Control) address of the network interface for that device. Its existence is a direct application of the general **cache** [class] principle to the specific problem of address resolution.

### Role in the Address Resolution Protocol (ARP)
The ARP protocol's fundamental job is to translate an IP address to a MAC address. This is necessary because Ethernet and similar link-layer technologies use MAC addresses for direct frame delivery, while IP operates at a higher logical layer. The ARP cache is the performance optimization layer for this process. When a host needs to send a packet to a local IP address, it first checks its ARP cache. A **cache hit** provides the MAC address immediately. A **cache miss** forces the host to broadcast an ARP request on the network, wait for a reply, and then store the new mapping in the cache for future use.

### Relationship to the General Cache Concept
As a **subclass_of** the general **cache** [class], the ARP cache shares the core characteristics defined for all caches: it **transparently stores data** (IP-MAC mappings) so that **future requests for that data can be served faster** (avoiding a network broadcast). It is a specific instance listed among key cache types, which include **CPU cache**, **disk cache**, **web cache**, and **negative cache**. Its purpose aligns with the primary goal of all caches: to **enhance computer performance** by reducing data-access time, in this case, network access time.

### Technical Implementation and Management
The ARP cache is implemented as a data structure (often a hash table) in the operating system kernel's network stack. Entries are added dynamically upon successful ARP replies. They are removed after a **timeout period** (e.g., 60-120 seconds on many systems) to prevent the use of outdated information if a device's IP or MAC changes. Some systems also implement **gratuitous ARP** to proactively update other hosts' caches. The cache size is typically limited, and entry replacement policies (like LRU - Least Recently Used) may be used when full.

### Ecosystem and Context
*   **Facet of ARP:** The ARP cache is intrinsically a **facet_of** the **Address Resolution Protocol**. It is not a separate protocol but an integral, optimizing component of ARP's operation.
*   **Wikipedia Presence:** The concept has a dedicated Wikipedia article titled **"ARP cache"** in **English**, **German**, and **French**, indicating its established notability in computing literature.
*   **Structured Data:** In knowledge graphs, it is identified by the **Google Knowledge Graph ID /g/121x71fn** and has a **sitelink_count** of **3**, reflecting its cross-wiki linkage. Its **wikidata_description** is the precise phrase "collection of Address Resolution Protocol entries".
*   **Alias:** It is also commonly referred to by the alias **"Table ARP"**.

### Distinction from Other Caches
While sharing the caching paradigm, the ARP cache is distinct from other major types:
*   **vs. CPU Cache:** CPU cache is a hardware, multi-level (L1/L2/L3) memory hierarchy built into the processor die to speed up access to main memory (RAM). The ARP cache is a software table in RAM used for network address translation.
*   **vs. Web/Disk Cache:** Web and disk caches store copies of larger, persistent data objects (web pages, file blocks) to avoid slower retrievals from remote servers or disk platters. The ARP cache stores only tiny, fundamental addressing records for immediate local network delivery.
*   **vs. Negative Cache:** A negative cache stores information about failed lookups (e.g., "this host is unreachable"). A standard ARP cache stores only successful, positive mappings, though a failed ARP request might not create a cache entry.