IP Generator - IPv4 Address

A public IP address is an IP address that is assigned to a device and is directly accessible over the internet. It is globally unique and used for communication between different networks.

Public IP addresses are assigned by Internet Service Providers (ISPs) and are required for any device that needs to communicate with other devices over the internet, such as websites, cloud servers, and VPN endpoints.

• 0.0.0.0/8 – Current network
• 10.0.0.0/8 – Private use
• 100.64.0.0/10 – Carrier-grade NAT
• 127.0.0.0/8 – Loopback
• 169.254.0.0/16 – Link-local (APIPA)
• 172.16.0.0/12 – Private use
• 192.0.0.0/24 – IETF protocol assignments
• 192.0.2.0/24 – TEST-NET-1 for documentation
• 192.88.99.0/24 – Deprecated 6to4 relay
• 192.168.0.0/16 – Private use
• 198.18.0.0/15 – Benchmarking
• 198.51.100.0/24 – TEST-NET-2 for documentation
• 203.0.113.0/24 – TEST-NET-3 for documentation
• 224.0.0.0/4 – Multicast
• 233.252.0.0/24 – Reserved for documentation
• 240.0.0.0/4 – Reserved (formerly experimental)
• 255.255.255.255/32 – Limited broadcast

Unlike private IP addresses, which are used within local networks and require NAT (Network Address Translation) to communicate with the internet, public IP addresses do not need NAT and can be directly routed on the global internet.

The term public IP address is specific to IPv4. In IPv6, a similar concept exists but is referred to as a global unicast address (GUA). IPv6 addresses do not require NAT and are designed to be globally routable.

A private IP address is an IP address that is reserved for use within local networks and is not routable on the public internet. These addresses are used for internal communication between devices within homes, offices, and enterprise environments.

Private IP addresses help conserve public IP space and provide a level of network security by keeping internal devices hidden from direct internet access. They require NAT (Network Address Translation) to communicate with the internet.

• 10.0.0.0/8 – Allows 16,777,216 total addresses
• 172.16.0.0/12 – Allows 1,048,576 total addresses
• 192.168.0.0/16 – Allows 65,536 total addresses

These ranges are defined in RFC 1918 and are commonly used in LAN (Local Area Network)environments.

Why Use Private IPs?

• Prevents exhaustion of public IP space
• Provides an additional layer of security by isolating internal devices
• Allows multiple organizations to use the same IP ranges without conflict
• Used in home routers, corporate networks, and cloud infrastructures

Unlike public IP addresses, private IPs cannot be accessed from the internet directly. Instead, they rely on a router or firewall with NAT to translate private addresses to public ones before traffic reaches the internet.

The 224.0.0.0/4 address block is reserved for multicast  communication in IPv4. It includes addresses from 224.0.0.0 to 239.255.255.255  and is used for one-to-many or many-to-many communication between networked devices.

How Multicast Works:

Unlike unicast (one-to-one) or broadcast (one-to-all) communication, multicast allows a device to send a packet to multiple recipients without sending separate copies to each. Devices interested in receiving multicast traffic join a multicast group using the Internet Group Management Protocol (IGMP).

Multicast Address Ranges:

• 224.0.0.0/24 – Link-local multicast: Reserved for routing protocols and other low-level topology discovery or maintenance protocols (e.g., OSPF, RIP, EIGRP, VRRP, IGMP). To see the full list of multicast address allocations, check the IPv4 Multicast Address Registry maintained by IANA .
• 224.0.1.0 - 224.0.1.255: Used for global (internet-wide) multicast applications.
• 232.0.0.0/8 – Source-Specific Multicast (SSM): Allows receivers to specify a single sender for the multicast stream.
• 233.0.0.0/8 – GLOP addressing: Allows organizations to use multicast IPs based on their AS number.
• 239.0.0.0/8 – Administratively Scoped Multicast: Used for private multicast within an organization (similar to private IPs).

Multicast is widely used in streaming media, stock market data feeds, real-time gaming, and routing protocol communications. Unlike broadcast, multicast traffic is only forwarded to devices that have explicitly joined a multicast group, reducing unnecessary network congestion.

The 169.254.0.0/16 address range is reserved for Link-Localaddresses in IPv4. These addresses are automatically assigned to network interfaces when a device fails to obtain an IP address from a DHCP server.

How Link-Local Works:

When a device cannot obtain an IP address dynamically from a DHCP server, it automatically assigns itself an address from the 169.254.0.0/16 range. This allows devices on the same local network to communicate without requiring manual configuration or a DHCP server.

Common Use Cases:

• Automatic Private IP Addressing (APIPA): Used by Windows, macOS, and Linux when DHCP fails.
• Direct Device-to-Device Communication: Enables devices to communicate in small local networks, such as printers, IoT devices, or ad-hoc networks.
• Fallback Addressing: Ensures that a device can still have an IP address even when DHCP is unavailable.

Limitations of Link-Local Addresses:

• Not Routable: Link-local addresses cannot be used beyond the local subnet. They are designed only for direct communication within the same network segment.
• Indicates a DHCP Issue: If a device gets a 169.254.x.x address, it usually means there is a problem with DHCP, or the network is not properly configured.
• No Internet Access: Devices with only a link-local address cannot access the internet without manual IP configuration.

The 127.0.0.0/8 address block is reserved for loopback functionality in IPv4. This means that any IP address in this range is used to refer to the local machine itself.

How Loopback Works:

When a packet is sent to an address in the 127.0.0.0/8 range, it is not transmitted over the network. Instead, it is processed internally by the device's operating system. This allows applications to communicate with themselves for testing, development, or inter-process communication.

Common Uses of the Loopback Address:

• Testing Network Applications: Developers use loopback addresses to test network applications without requiring an external network connection.
• Inter-Process Communication (IPC): Applications running on the same machine can use loopback addresses to exchange data efficiently.
• Localhost Resolution: The address 127.0.0.1 is commonly mapped to the hostname localhost, making it a universal way to reference the local system.

Key Characteristics:

• Not Routable: Loopback addresses are never sent to external networks.
• Fully Handled by the OS: The operating system intercepts all traffic directed to 127.0.0.0/8 and processes it locally.
• Single-Device Use: Only the device itself can use its loopback addresses; they are not accessible by other networked devices.

The following IPv4 address ranges are reserved for documentation and educational purposes. They are not assigned to any real network and should only be used in examples, training materials, and technical documentation.

Documentation Address Ranges:

• 192.0.2.0/24 (TEST-NET-1): Used in documentation to illustrate IPv4 networking concepts.
• 198.51.100.0/24 (TEST-NET-2): Reserved for similar purposes as TEST-NET-1.
• 203.0.113.0/24 (TEST-NET-3): Another documentation range meant for technical examples.
• 233.252.0.0/24: Reserved for multicast documentation.

Why Use These Addresses?

These addresses are meant to prevent accidental conflicts with real-world networks. They ensure that example configurations, training materials, and guides do not interfere with production environments.

Important Notes:

• These addresses should never be used in live networks or assigned to real devices.
• They are widely used in RFCs, networking books, and educational resources.
• If example addresses are needed, these should be used instead of real IP allocations.

The 100.64.0.0/10 address block is reserved for Carrier-Grade NAT (CGNAT). It is used by Internet Service Providers (ISPs) to assign private addresses to customers while sharing a limited number of public IPv4 addresses.

How Carrier-Grade NAT Works:

As IPv4 addresses become increasingly scarce, ISPs use CGNAT to allow multiple customers to share a single public IP address. This is done by assigning customers addresses from the 100.64.0.0/10  range and translating their traffic through a centralized NAT system before reaching the internet.

Key Characteristics:

• Not Routable on the Public Internet: Addresses in this range cannot be accessed directly from the internet and require NAT.
• Shared by Multiple Customers: ISPs use CGNAT to allow many users to share a limited pool of public IPs.
• Different from Private IP Ranges: Unlike private IPs (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), this range is intended for ISP-level NAT, not internal LAN use.

Limitations of CGNAT:

• Breaks End-to-End Connectivity: Since multiple users share a public IP, some applications (e.g., gaming, VPNs, peer-to-peer connections) may not function properly.
• Can Cause Rate Limiting: Some websites impose connection limits per IP, which can affect users behind CGNAT.
• Increases Latency: Additional NAT processing can introduce delays in traffic routing.

The 198.18.0.0/15 address block is reserved for network benchmarking and testing. This range is specifically designated for use in network performance evaluation and testing scenarios, particularly for testing inter-network communications between devices.

Purpose of 198.18.0.0/15:

Unlike standard private IP ranges or public address spaces, this range is meant for controlled testing environments. It is typically used by network vendors, researchers, and organizations to measure network performance, including:

• Evaluating network equipment performance.
• Simulating inter-network communication for research.
• Testing firewalls, routers, and security policies in an isolated environment.

Key Characteristics:

• Not Routable on the Public Internet: This range should only be used in closed testing environments.
• Defined by RFC 2544: The RFC 2544 benchmark testing standard defines its use in network performance evaluations.
• Not for General Private Use: Unlike 10.0.0.0/8 or 192.168.0.0/16, this range is reserved explicitly for testing and should not be used in production networks.

Why This Range Exists:

The 198.18.0.0/15 range was reserved to ensure that performance testing does not interfere with real-world networks. Without a dedicated range, testing using normal IP addresses could cause unintended routing issues or impact live network operations.

The 192.88.99.0/24 address block was originally designated for IPv6-to-IPv4 relay services. It was used to facilitate communication between IPv6 networks and the IPv4 internet using the 6to4 tunneling mechanism.

How 192.88.99.0/24 Worked:

This range was assigned to act as a relay anycast address, meaning that packets sent to an address in this block were routed to the nearest 6to4 relay. These relays allowed IPv6-only hosts to access IPv4 content by encapsulating IPv6 traffic within IPv4 packets.

Key Characteristics:

• Used for 6to4 Tunneling: Enabled IPv6 networks to communicate with IPv4 without native IPv6 support.
• Routed Anycast Address: Traffic was forwarded to the closest available 6to4 relay, reducing latency.
• Deprecated by IETF: The use of this range for IPv6 transition was officially deprecated in RFC 7526.

Why It Was Deprecated:

The 6to4 transition method faced operational challenges, including unreliable relay availability and security risks. As a result, the IETF recommended discontinuing its use in favor of modern IPv6 deployment strategies, such as native IPv6 and dual-stack implementations.

The 192.0.0.0/24 address block is reserved for Dual-Stack Lite (DS-Lite), a technology designed to help Internet Service Providers (ISPs) transition from IPv4 to IPv6 by tunneling IPv4 traffic over an IPv6 network.

How DS-Lite Works:

DS-Lite allows ISPs to provide IPv4 connectivity to customers over an IPv6-only infrastructure. Instead of assigning public IPv4 addresses to end users, ISPs use Carrier-Grade NAT (CGNAT)  combined with IPv6 tunneling. Devices with only IPv6 addresses send IPv4 traffic encapsulated in IPv6 packets to a DS-Lite gateway, where it is translated and routed to the IPv4 internet.

Key Characteristics:

• Encapsulates IPv4 in IPv6: IPv4 traffic is tunneled inside IPv6 packets.
• Uses Carrier-Grade NAT (CGNAT): IPv4 addresses are shared among multiple customers.
• Relies on the AFTR (Address Family Transition Router): The AFTR is responsible for decapsulating IPv4 traffic and forwarding it to the internet.
• Defined in RFC 6333: DS-Lite is officially described inRFC 6333.

Advantages of DS-Lite:

• Extends the Life of IPv4: ISPs can continue supporting IPv4 services while transitioning to IPv6.
• Reduces IPv4 Address Exhaustion: Since public IPv4 addresses are shared, ISPs do not need to assign one per customer.
• Encourages IPv6 Deployment: Customers are given native IPv6 connectivity while still supporting legacy IPv4.

Limitations of DS-Lite:

• No Direct IPv4 Address Assignment: End users do not receive a public IPv4 address.
• Breaks Some IPv4 Applications: Peer-to-peer, gaming, and VoIP services may not work correctly without additional configuration.
• Increases Latency: IPv4 packets must be encapsulated and processed by an AFTR gateway.

The unspecified address, represented as 0.0.0.0/32, is a special IPv4 address that signifies the absence of a specific address. It is commonly used in networking for various purposes, such as routing and socket programming.

Common Uses of 0.0.0.0:

• Default Route Placeholder: In routing tables, 0.0.0.0/0 is used to define the default gateway, meaning "any address that does not match a more specific route."
• Binding to All Interfaces: When a server application binds to 0.0.0.0, it listens on all available network interfaces instead of a specific IP.
• DHCP Client Requests: Before an IP address is assigned by DHCP, a client may use  0.0.0.0 as its source address when requesting an IP lease.
• Indicating No Specific IP: When a device does not have an assigned IP or is in an unconfigured state, it may use 0.0.0.0 to indicate "no address."

The 0.0.0.0/8 address block is reserved for referring to the current networkand has historical use cases in early networking systems. Today, most of this range is either unused or reserved for specific networking functions.

Common Uses of 0.0.0.0/8:

• Unspecified Address (0.0.0.0/32): The individual address 0.0.0.0 is part of this block and is commonly used to indicate "no specific IP address" or bind to all interfaces on a host.
• Routing and Default Routes: The subnet 0.0.0.0/0 is often used as the default route, meaning "match any address if no other specific route exists."

While this range was originally intended to refer to the current network in early networking designs, its practical use has mostly faded. The address 0.0.0.0 itself remains widely used, but the broader 0.0.0.0/8 is generally unused in modern networking.