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Reserved IPv4 Ranges

You landed here because the address you looked up falls inside an IANA special-purpose range that is not delegated to any operator. Unlike RFC 1918 private space or multicast, the ranges below do not share a single purpose — each one was carved out by a different RFC for a different reason.

0.0.0.0/8

RFC 1122

“This host on this network.” Used as the source address before a host acquires DHCP and as the destination in default-route notation (“0.0.0.0/0”). Should never appear on the wire outside DHCPDISCOVER.

192.0.0.0/24

RFC 6890

IETF protocol assignments. Individual addresses inside this /24 are assigned to specific protocols (NAT64, Port Control Protocol, etc.) rather than delegated to an operator.

198.18.0.0/15

RFC 2544

Network-device benchmarking. Reserved for throughput and latency tests so that synthetic test traffic does not collide with real production networks.

240.0.0.0/4

RFC 1112

The former Class E space. Reserved for “future use” since 1989, and still unusable today because too many TCP/IP stacks hard-code it as invalid. Proposals to reclaim it as regular unicast have consistently been rejected.

Frequently asked questions

What is 0.0.0.0 used for?

0.0.0.0 is the 'this host on this network' address per RFC 1122. It is the default source address for a host that does not yet have a DHCP lease, and the default destination in a default route ('0.0.0.0/0 next-hop ...'). The entire 0.0.0.0/8 block is reserved and should never appear as a source or destination on the wire in production.

Why is 198.18.0.0/15 reserved?

RFC 2544 (published 1999) reserves 198.18.0.0/15 for benchmarking network interconnect devices. When vendors test switch and router throughput, loss, and latency, they generate synthetic traffic between 198.18.x.x and 198.19.x.x to avoid polluting real routing tables. Seeing this range in a packet capture means you are looking at an iperf/Ixia/Spirent test or a misconfigured lab.

Will 240.0.0.0/4 ever be usable?

Probably not. RFC 1112 reserved 240.0.0.0/4 (the old Class E space) in 1989 as 'reserved for future use'. Periodic proposals to reclaim it as regular unicast space have been rejected because too many implementations hard-code it as invalid. The real-world plan for IPv4 exhaustion is IPv6, not reclaiming Class E — so 240/4 remains a 268-million-address block that you cannot assign to anything.

What is 192.0.0.0/24 reserved for?

192.0.0.0/24 is the 'IETF protocol assignments' block per RFC 6890. Individual addresses inside it are assigned to specific protocols — for example 192.0.0.8 is the IPv4 dummy address, 192.0.0.9 is the Port Control Protocol anycast, 192.0.0.170 is NAT64/DNS64 discovery. Each entry is a protocol, not a network, and none of them are delegated to an operator.

Why does ipctl show no data for these?

ipctl derives its IP data from RIR delegated-stats files, live BGP routing, and third-party geolocation databases. Reserved ranges never appear in any of those sources because no RIR delegates them, no operator announces them, and no geolocation vendor tracks them. There is nothing to show.

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