E.164
The international public telecommunication numbering plan used for telephone numbers. ENUM can represent an E.164 number as labels beneath e164.arpa for DNS-based service discovery.
Read definitionAlphabetical glossary
E glossary terms
21 definitions beginning with E.
21 terms
ECS
EDNS Client Subnet, an EDNS option that lets a resolver include part of a client's network prefix in an upstream query so an authoritative service can tailor the answer geographically. It can improve content localization but reduces privacy and cache efficiency.
Read definitionEDE
Extended DNS Error, an EDNS option that adds a more specific reason to a DNS response, such as blocked, stale answer, DNSSEC bogus, or network error. The normal RCODE remains present.
Read definitionEDNS
Extension Mechanisms for DNS, a framework that expands DNS message capabilities without changing the original fixed header. An OPT pseudo-record carries a larger UDP size, the extended RCODE, version, flags, and options.
Read definitionEDNS buffer size
The UDP payload size a requester advertises in the OPT record. Oversized values can cause fragmentation or path failures, while undersized values cause more truncation and TCP or QUIC fallback.
Read definitionEDNS Client Subnet
The full name of ECS, an option that shares a truncated client network prefix with upstream authoritative systems. Operators should understand its privacy, caching, and traffic-steering effects.
Read definitionEDNS Cookie option
The EDNS option used to transport DNS Cookies between client and server. It helps verify return reachability and harden UDP exchanges against spoofing.
Read definitionEDNS Keepalive
An EDNS option used with DNS over TCP to signal a desired idle timeout for a persistent connection. It can reduce repeated connection setup while allowing servers to control resource use.
Read definitionEDNS option
A typed extension carried inside the OPT pseudo-record. Registered options include NSID, Cookies, Client Subnet, Padding, Extended DNS Error, TCP Keepalive, Chain, and multiple experimental or specialized functions.
Read definitionEDNS Padding
An EDNS option that adds padding bytes to DNS messages so packet sizes reveal less information about the queried name or response. It is especially useful with encrypted DNS transports.
Read definitionEDNS version
A field in the OPT record that identifies the EDNS version. EDNS version 0 is the deployed standard; unsupported versions normally produce BADVERS.
Read definitionEgress filtering
Network filtering that blocks packets with invalid or unauthorized source addresses from leaving a network. It is a major defense against source-address spoofing used in DNS reflection attacks.
Read definitionEnterprise number
A Private Enterprise Number assigned by IANA to an organization. DHCP vendor-specific identifiers, DUID-EN values, and many management protocols use enterprise numbers to distinguish namespaces.
Read definitionENUM
A system for mapping E.164 telephone numbers into DNS names and retrieving service information through NAPTR records. Digits are reversed and represented beneath e164.arpa.
Read definitionEUI-48
A 48-bit Extended Unique Identifier, commonly the format used for Ethernet MAC addresses. DHCP reservations and DUID types often derive identity from a link-layer address.
Read definitionEUI-64
A 64-bit Extended Unique Identifier format. Modified EUI-64 was historically used to form IPv6 interface identifiers from MAC addresses, though modern systems often use privacy or stable-random identifiers instead.
Read definitionExclusion
An address or range inside a DHCP scope or subnet that the server must not lease dynamically. Exclusions are used to protect statically assigned infrastructure or address blocks managed elsewhere.
Read definitionEXPIRE
The SOA field that tells a secondary how long it may continue serving a zone without successfully refreshing from an upstream source. After the interval, the zone becomes expired and should no longer be served authoritatively.
Read definitionExpired lease
A lease whose valid lifetime has ended. The server may return the address or prefix to an available state after any configured hold-down, cleanup, or conflict-check process.
Read definitionExtensible attribute
A custom metadata field attached to a DDI object, such as owner, environment, business unit, site, application, or lifecycle state. In Infoblox NIOS, Extensible Attributes are widely used for search, policy, automation, and reporting.
Read definitionExternal DNS
Authoritative DNS intended to answer public or partner-facing queries, typically with recursion disabled and tightly controlled zone transfer and update access. It is often separated from internal DNS by servers, views, networks, or accounts.
Read definition