T1
The renewal timer. DHCPv4 clients normally begin unicast renewal at T1, often 50 percent of lease time; DHCPv6 identity associations also carry T1 values.
Read definitionAlphabetical glossary
T glossary terms
24 definitions beginning with T.
24 terms
T2
The rebinding timer. If renewal has not succeeded by T2, the client broadens its attempt to any available server, often around 87.5 percent of DHCPv4 lease time by default.
Read definitionTag
A label or key-value marker used to categorize DDI objects for search, automation, access control, reporting, or lifecycle policy. The exact feature may be called metadata, extensible attribute, or custom property.
Read definitionTC bit
The Truncated bit in a DNS response indicates that the message was shortened because it exceeded the available transport size. A client normally retries using TCP or another suitable transport.
Read definitionTCP fallback
Retrying a DNS query over TCP after a truncated UDP response or other transport need. Modern DNS implementations must support TCP and should reuse connections efficiently.
Read definitionTenant
An administrative partition for a customer, business unit, environment, or application. Tenants may have isolated permissions, zones, address spaces, VRFs, and policies.
Read definitionTentative address
An IPv6 address assigned to an interface but not yet usable for normal communication while Duplicate Address Detection is in progress.
Read definitionTFTP
Trivial File Transfer Protocol, a simple UDP-based file transfer protocol traditionally used for PXE boot, device configuration, and firmware. It lacks strong security and should be constrained to trusted networks.
Read definitionThaw
A BIND operation that resumes dynamic update after a zone has been frozen and reloads changes made to its master file.
Read definitionThreat intelligence
Information about malicious domains, addresses, infrastructure, campaigns, and behavior used to support detection or blocking. DNS security systems must manage confidence, freshness, false positives, and policy exceptions.
Read definitionTime to live (TTL)
The number of seconds a DNS record may be cached before it must be treated as expired. TTL choices affect change speed, query load, resilience, and negative or stale-answer behavior.
Read definitionTLD
Top-Level Domain, a direct child of the DNS root, such as com, org, net, or a country-code TLD. TLD zones are delegated from the root.
Read definitionTLSA record
A record that associates a TLS service with an expected certificate or public key using usage, selector, and matching fields. Secure use depends on DNSSEC validation.
Read definitionTopology ruleset
A DTC policy object that maps client, resolver, network, geography, or extensible-attribute conditions to an ordered set of pools or destinations.
Read definitionTransaction ID
A 16-bit identifier used to match a DNS response to its query. UDP security also relies on source port, addresses, question content, cookies, and other transaction checks.
Read definitionTransaction signature (TSIG)
A shared-secret mechanism that authenticates DNS messages and protects integrity and replay context. It is commonly used for zone transfers, NOTIFY, and dynamic updates between trusted systems.
Read definitionTransfer source
The authoritative server from which a secondary requests AXFR or IXFR. The transfer source may be a hidden primary, another secondary, or a distribution layer.
Read definitionTrap
An unsolicited management notification, commonly an SNMP trap, sent when an event or threshold occurs. DDI traps can report HA changes, pool exhaustion, service failure, or security events.
Read definitionTruncation
The condition indicated by the TC bit when a response does not fit the allowed message size. Truncation should prompt retry over a transport that can carry the full response.
Read definitionTrust anchor
A configured DNSKEY or DS record that a validator accepts as the starting point for a chain of trust. The root DNSKEY is the most common public-DNS trust anchor.
Read definitionTSIG
The common abbreviation for Transaction Signature, a shared-secret authentication mechanism for DNS messages. Current TSIG specification is RFC 8945.
Read definitionTTL
Abbreviation for Time to Live, the cache lifetime carried in each resource record. Records in one RRset should have a consistent TTL.
Read definitionTXT record
A Text record contains one or more character strings, each limited to 255 octets in wire format. TXT is used by many applications for verification, email policy, security, and metadata, with application-specific syntax.
Read definitionType bitmap
A compact bitmap listing the resource-record types present at an owner name, used in NSEC and NSEC3 records to prove the absence of a requested type.
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