APIPA
Automatic Private IP Addressing, the Microsoft term for self-assignment from 169.254.0.0/16 when a host cannot obtain normal IPv4 configuration. These link-local addresses are not routed.
Category glossary
Search all termsIPv4
13 definitions associated with IPv4.
ARP
The Address Resolution Protocol maps an IPv4 address to a link-layer address on a local network. Duplicate IPs, stale caches, and spoofing can cause misleading DDI troubleshooting symptoms.
ARP probe
An ARP-based check used before assigning or using an IPv4 address to determine whether another device appears to claim it. DHCP servers or clients may use probes as part of conflict detection.
Broadcast
Delivery to all hosts on a local broadcast domain. DHCPv4 clients initially use broadcasts because they may not yet know their address, server, or default gateway.
Broadcast address
The highest address in a traditional IPv4 subnet, used to reach all hosts on that subnet. Modern point-to-point /31 networks are an important exception.
Carrier-grade NAT (CGN)
Large-scale address translation used by service providers to share public IPv4 addresses among customers, commonly using 100.64.0.0/10 on the provider side. CGN complicates attribution and end-to-end address visibility.
DHCPv4
The DHCP protocol used to configure IPv4 hosts. It uses UDP ports 67 and 68 and commonly follows the Discover, Offer, Request, Acknowledge sequence.
In-addr.arpa
The DNS reverse-mapping domain for IPv4. Address octets are reversed as labels below in-addr.arpa, with zone boundaries aligned to delegated portions of address space.
IPv4 link-local
Addresses from 169.254.0.0/16 that a host may self-assign for local-link communication when normal configuration is unavailable. They should not be routed.
Network address
The first address in a traditional IPv4 subnet, representing the subnet itself rather than an ordinary host. Point-to-point /31 behavior is an important exception.
PAT
Port Address Translation, a form of NAT that maps many internal connections to one or a few external addresses by translating transport ports. It is often called NAT overload.
Shared address space
The IPv4 block 100.64.0.0/10 reserved for service-provider shared-address use, especially carrier-grade NAT. It is not an RFC 1918 private block.
Subnet mask
A 32-bit mask identifying network and host bits in an IPv4 address. Contiguous masks are represented more compactly by CIDR prefix length.