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Special-Use IPv4 Ranges (Detailed Notes)

Special-Use IPv4 Address Ranges (RFC-Defined Network Behavior)

Overview
Not all IP addresses are intended for public routing, end-user devices, or general network operations. Some IPv4 ranges are reserved by IANA and defined in RFCs for very specific, highly controlled purposes. These include loopback ranges, link-local space, benchmarking networks, documentation blocks, and addresses used for protocol infrastructure.

Understanding special-use IPv4 ranges is essential for:

  • Troubleshooting routing problems
  • Avoiding misconfiguration
  • Ensuring compliance with RFC standards
  • Detecting spoofing or unusual traffic
  • Designing enterprise and cloud network architectures

This CSV provides the authoritative, RFC-accurate list of special IPv4 ranges, along with deep technical notes explaining how each range behaves and when it should — or should not — appear on the network.

What This CSV Contains

For each special-purpose range, the file includes:

  • CIDR block
  • Name / classification
  • Detailed technical explanation
  • RFC references and behavior rules

Examples included:

  • 127.0.0.0/8 — Loopback
  • 169.254.0.0/16 — Link-Local APIPA
  • 100.64.0.0/10 — Carrier-Grade NAT
  • 192.0.2.0/24 — TEST-NET-1
  • 224.0.0.0/4 — Multicast
  • 240.0.0.0/4 — Reserved
  • And many more

Why This Matters

Special-use IP ranges frequently appear in:

  • Firewall logs
  • SIEM alerts
  • Packet captures
  • Cloud infrastructure telemetry
  • Malicious scans
  • Routing protocol operations

Engineers often get confused when they see these addresses. This table gives you clean, reliable guidance on what each one means, and how it behaves.

This page should live as part of your IPv4 Knowledge Base, and any engineer who lands on it will immediately trust your expertise.

CIDRNameDetailed Notes
0.0.0.0/8This Network BlockUsed when a host does not yet know its IP. 0.0.0.0 as source = 'I don't have an IP yet'. Also used for DHCPDISCOVER and default-route representation. Never manually assigned; should not appear on routed networks.
0.0.0.0/32Default RouteRepresents 'anywhere' in routing tables. Not an assignable host address.
255.255.255.255/32Limited BroadcastBroadcast to local Layer 2 domain only. Never routed. Used for ARP, DHCP, discovery protocols. Should never appear on routed interfaces.
10.0.0.0/8Private IPv4 SpaceMassive internal-use block. Ideal for large enterprises, campus backbones, multi‑region networks. Routable internally, not globally. Commonly subnetted into /16, /20, /24. RFC1918.
172.16.0.0/12Private IPv4 SpaceMid‑sized private block. Often used for VPN pools, server farms, segmentation. Easier to avoid conflicts than 192.168/16. RFC1918.
192.168.0.0/16Private IPv4 SpaceMost common home/SMB network space. Frequently used for VLANs, SOHO networks. High collision risk when merging networks (VPNs, acquisitions). RFC1918.
169.254.0.0/16Link‑Local APIPAAuto‑assigned when DHCP fails. Never routed. Used for local‑only communication, mDNS, device discovery. Seeing these in logs indicates DHCP problems. RFC3927.
127.0.0.0/8Loopback RangeEntire /8 loops back to local host. Typically only 127.0.0.1 used, but all addresses are valid loopbacks. Critical for local testing & inter‑process communication. Packets should never appear on the wire. RFC1122.
100.64.0.0/10Carrier‑Grade NATUsed by ISPs for large scale NAT44 to preserve IPv4 space. Not for enterprise LAN use. Appearing internally indicates misconfiguration or ISP interference. RFC6598.
192.0.0.0/24IETF Protocol AssignmentsReserved for protocol level functionality, transition mechanisms, and experimental uses. Rarely appears in enterprise networks. RFC5736.
192.0.2.0/24TEST‑NET‑1Documentation & training examples. Must NOT be used in production networks. RFC5737.
198.51.100.0/24TEST‑NET‑2Documentation & training examples. Safe for examples; never routed publicly. RFC5737.
203.0.113.0/24TEST‑NET‑3Documentation & training examples. Used in textbooks, diagrams, labs. RFC5737.
198.18.0.0/15Benchmarking RangeUsed for performance testing of routers, firewalls, and other devices. Reserved for benchmark labs; not intended for general networking. RFC2544.
224.0.0.0/4Multicast RangeAll multicast traffic (IGMP, mDNS, routing protocols). 224.0.0.0 224.0.0.255 reserved for local‑network control. 239.0.0.0/8 for administratively scoped multicast.
240.0.0.0/4Reserved (Future Use)Experimental block. Not publicly routed. Historically unsupported, but modern OSes can route some of this block. Still considered reserved.
192.88.99.0/24Deprecated 6to4 RelayFormerly used for IPv6 transition. Deprecated and removed from global routing. Should not be used. RFC7526.
192.175.48.0/24AS112 SinkholeUsed for reverse‑DNS leaks and misconfigured private DNS queries. Operated by volunteer AS112 nodes to absorb misdirected traffic.
233.252.0.0/14Documentation MulticastTEST MULTICAST range for documentation. Never used in production multicast deployments. RFC6034.
255.0.0.0/8ReservedReserved for future definition. Not assignable. Not routed. Packets from this block indicate spoofing or misconfiguration.