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DNS Providers to Cease Implementing DNS Resolver Workarounds

Starting on February 1, 2019, a number of DNS software and service providers will cease implementing DNS resolver workarounds for systems that don’t follow the Extensions to DNS (EDNS) protocol. 

Starting on February 1, 2019, a number of DNS software and service providers will cease implementing DNS resolver workarounds for systems that don’t follow the Extensions to DNS (EDNS) protocol. 

Intended for DNS Flag Day, the switch should solve two major problems DNS has at the moment due to these workarounds: slower responses to DNS queries and the difficulty of deploying new DNS protocol features such as improved distributed denial of service protections.

Although the Extension Mechanisms for DNS were specified in 1999 to establish rules for responding to queries with EDNS options or flags, some implementations continue to violate the rules. To address interoperability issues, DNS software developers implemented workarounds for non-standard behaviors. 

“These workarounds excessively complicate DNS software and are now also negatively impacting the DNS as a whole,” the Internet Systems Consortium (ISC) points out

To address the problem, some organizations have agreed to update their software or systems to cease implementing said workarounds in software set to be released around DNS Flag Day. These include ISC (in BIND 9.14 stable), CZ NIC (in Knot Resolver 3.3.0 – it has stricter EDNS handling in all current versions), NLNET Labs (in Unbound 1.8.4, 1.9.0 and newer), and PowerDNS (PowerDNS recursor 4.2). 

Organizations supporting the initiative include Cisco, CleanBrowsing, Cloudflare, Facebook, Google, Quad9, and the aforementioned software vendors of DNS software and public DNS providers. 

“To ensure further sustainability of the system it is time to end these accommodations and remediate the non-compliant systems. This change will make most DNS operations slightly more efficient, and also allow operators to deploy new functionality, including new mechanisms to protect against DDoS attacks,” the initiative’s GitHub page reveals. 

This change is expected to have impact on sites operating non-compliant software only. Internet users with their own domain names will be affected only indirectly and won’t need to take specific action. 

“Domains served by DNS servers that are not compliant with the standard will not function reliably when queried by resolvers that have been updated to the post-Flag Day version, and may become unavailable via those updated resolvers,” ISC points out. 

Organizations with DNS zones served by non-compliant servers will see their online presence slowly degrade or disappear when ISPs and other organizations update their resolvers. Organizations switching internal DNS resolvers to versions that don’t implement workarounds might experience issues with sites and email servers becoming unreachable.

Operators of DNS authoritative systems are advised to check their own domain at to ensure they are EDNS-compliant. Common issues emerge from firewalls blocking EDNS traffic and old DNS servers requiring upgrades.

Related: Google Secures Public DNS Queries With DNS-over-TLS

Related: Mozilla Testing DNS-over-HTTPS in Firefox

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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