EDNS

This document describes an EDNS(0) option that can be used between DNS Update Requesters and authoritative DNS servers to include a lifetime (lease duration) in a DNS Update or DNS Update Response, allowing a server to garbage collect stale Resource Records that have been added by DNS Updates if they are not renewed.

RFC 7830 specifies the "Padding" option for Extension Mechanisms for DNS (EDNS(0)) but does not specify the actual padding length for specific applications. This memo lists the possible options ("padding policies"), discusses the implications of each option, and provides a recommended (experimental) option.

This document describes an Extension Mechanisms for DNS (EDNS0) option that is in active use to carry information about the network that originated a DNS query and the network for which the subsequent response can be cached. Since it has some known operational and privacy shortcomings, a revision will be worked through the IETF for improvement.

This document specifies the EDNS(0) "Padding" option, which allows DNS clients and servers to pad request and response messages by a variable number of octets.

DNS messages between clients and servers may be received over either UDP or TCP. UDP transport involves keeping less state on a busy server, but can cause truncation and retries over TCP. Additionally, UDP can be exploited for reflection attacks. Using TCP would reduce retransmits and amplification. However, clients commonly use TCP only for retries and servers typically use idle timeouts on the order of seconds.

This document defines an EDNS0 option ("edns-tcp-keepalive") that allows DNS servers to signal a variable idle timeout. This signalling encourages the use of long-lived TCP connections by allowing the state associated with TCP transport to be managed effectively with minimal impact on the DNS transaction time.

This document specifies a method for secondary DNS servers to honour the SOA EXPIRE field as if they were always transferring from the primary, even when using other secondaries to perform indirect transfers and refresh queries.

The DNS Security Extensions (DNSSEC) were developed to provide origin authentication and integrity protection for DNS data by using digital signatures. These digital signatures can be generated using different algorithms. This document specifies a way for validating end-system resolvers to signal to a server which digital signature and hash algorithms they support. The extensions allow the signaling of new algorithm uptake in client code to allow zone administrators to know when it is possible to complete an algorithm rollover in a DNSSEC-signed zone.

The Domain Name System's wire protocol includes a number of fixed fields whose range has been or soon will be exhausted and does not allow requestors to advertise their capabilities to responders. This document describes backward-compatible mechanisms for allowing the protocol to grow.

This document updates the Extension Mechanisms for DNS (EDNS(0)) specification (and obsoletes RFC 2671) based on feedback from deployment experience in several implementations. It also obsoletes RFC 2673 ("Binary Labels in the Domain Name System") and adds considerations on the use of extended labels in the DNS.