P-code
A generic informal reference to a protocol or algorithm code point. Documentation should use the exact registry field, such as DNSSEC algorithm number, digest type, or option code, to avoid ambiguity.
Read definitionAlphabetical glossary
P glossary terms
39 definitions beginning with P.
39 terms
PAD option
A zero-length or padding option used to align or fill option areas without conveying configuration. DHCPv4 option 0 is Pad.
Read definitionParent zone
The zone immediately above a delegated child zone. It publishes the delegation NS RRset, optional DS records, and any required glue.
Read definitionPartner down
A failover state in which one server is administratively or automatically authorized to assume broader responsibility because its peer is considered unavailable. Entering the state incorrectly can create duplicate allocation risk.
Read definitionPassive DNS
A system that collects and indexes observed DNS query or response data over time without actively probing every name. It supports investigations, threat intelligence, asset discovery, and historical correlation.
Read definitionPAT
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.
Read definitionPD
Common abbreviation for Prefix Delegation. DHCPv6 PD assigns a prefix to a requesting router rather than only assigning a single interface address.
Read definitionPeer-address
A field in a relay message identifying the client or previous relay from which the message was received. It helps preserve the relay chain and return path.
Read definitionPEN
Private Enterprise Number, an IANA-assigned numeric identifier for an organization. PENs namespace vendor-specific data in DHCP, SNMP, DUIDs, and other protocols.
Read definitionPer-link configuration
Configuration selected based on the client's network link, usually identified by GIADDR, link-address, interface, relay information, or subnet selection options.
Read definitionPersistent connection
A TCP, TLS, QUIC, or other session reused for multiple DNS transactions rather than opened for each query. Persistence improves efficiency but requires connection limits and idle-time management.
Read definitionPersistent record
A record protected from automatic aging, scavenging, cleanup, or synchronization deletion. The term is product-specific and does not define a distinct DNS resource-record type.
Read definitionPing
A diagnostic operation that sends ICMP echo requests and measures replies. Ping tests IP reachability, not DNS correctness or application availability, and devices may intentionally ignore it.
Read definitionPool
A collection of resources from which a service selects a member. In DHCP it is an address range; in GSLB or load balancing it is a group of application endpoints.
Read definitionPool exhaustion
A state in which no eligible addresses or prefixes remain for new clients. Causes include genuine growth, excessive lease duration, starvation attacks, stale leases, exclusions, or a poorly sized subnet.
Read definitionPort
A transport-layer number used by TCP, UDP, SCTP, or DCCP to identify an application endpoint. DNS commonly uses port 53, DHCPv4 uses 67/68, and DHCPv6 uses 546/547.
Read definitionPre-provisioning
Creating addresses, reservations, DNS records, options, or metadata before a device or service is activated. Good workflows include ownership, expiration, and cleanup controls to prevent permanent stale data.
Read definitionPref64
An IPv6 prefix used by NAT64 to embed or represent IPv4 destinations. Networks can advertise a Pref64 in Router Advertisements, and DNS64 uses a configured prefix for synthesis.
Read definitionPreference
A relative selection value whose interpretation depends on the protocol. MX and SRV use numeric preference or priority, while DHCPv6 servers can send an OPTION_PREFERENCE value to influence client selection.
Read definitionPreferred lifetime
The period during which an IPv6 address or prefix is preferred for new communication. After it expires but before valid lifetime ends, the resource is deprecated and should generally not be selected for new sessions.
Read definitionPrefix
A contiguous IP address block identified by leading network bits and a prefix length. Prefixes support routing aggregation, subnetting, allocation, and policy.
Read definitionPrefix delegation
A DHCPv6 function that assigns prefixes to routers for downstream use. It separates routed-prefix allocation from individual host-address assignment.
Read definitionPrefix Information Option (PIO)
A Router Advertisement option describing an IPv6 prefix, its valid and preferred lifetimes, and whether it is on-link or autonomous for SLAAC.
Read definitionPrefix length
The number of leading bits that identify the network portion of an address, written after a slash. Larger prefix-length numbers represent smaller address blocks.
Read definitionPrefix policy
Host rules that rank source and destination address pairs, influencing address selection when multiple IPv4 and IPv6 choices exist. Policy can affect which DNS answer a client actually uses.
Read definitionPrefix utilization
A measure of how much child space within an aggregate prefix has been allocated or assigned. It differs from host-address utilization inside a single subnet.
Read definitionPrimary DNS server
The authoritative server or data source from which a zone is provisioned and updated before changes reach secondaries. "Primary" describes the provisioning relationship, not necessarily traffic preference or a single server.
Read definitionPrimary zone
A locally writable authoritative zone whose source data is maintained on that server or integrated data store. Other servers can obtain copies through transfer or replication.
Read definitionPrivate address
An address intended for private networks rather than direct global routing. IPv4 private blocks are defined by RFC 1918, while IPv6 Unique Local Addresses use fc00::/7 with locally assigned space commonly from fd00::/8.
Read definitionPrivate hosted zone
A cloud-managed authoritative zone visible only within associated virtual networks, accounts, or resolver endpoints. Connectivity and resolver rules determine who can query it.
Read definitionPrivate namespace
A DNS namespace intended for limited administrative or network scope rather than the public DNS. Collision risk exists if an internal suffix later becomes delegated publicly or is used by another connected organization.
Read definitionPrivate-use option
An option code range reserved for local or vendor use rather than global standardization. Private-use codes can collide when devices or organizations expect different meanings.
Read definitionProbe
An active test used to measure reachability, latency, correctness, or service health. DNS probes may query specific names and validate answers, flags, timing, and server identity.
Read definitionProtective DNS
A recursive DNS service that uses threat intelligence and policy to block or redirect access to malicious domains while producing security telemetry. It can be delivered on premises, in cloud, or as a hybrid service.
Read definitionProvisioning
The automated or manual creation and delivery of DDI configuration for a new service, device, site, or tenant. Provisioning should include validation, ownership, rollback, and post-change checks.
Read definitionPTR record
A Pointer record maps a reverse-domain name to another domain name, most commonly mapping an IPv4 or IPv6 address to a host name. Multiple PTRs are technically possible but can confuse applications.
Read definitionPublic suffix
A domain suffix under which independent parties can register names, such as com or co.uk, as identified by policy data such as the Public Suffix List. It is not always the same as a DNS zone boundary.
Read definitionPunycode
The encoding algorithm used by IDNA to represent Unicode labels using ASCII characters. Encoded A-labels begin with xn--.
Read definitionPXE
Preboot Execution Environment, a framework that uses DHCP and a boot transfer protocol to start a system from the network. DHCP identifies architecture, boot server, and boot file or menu information.
Read definition