Cyber Alerts

DNS Flag Day 2019

Q: What should you do now?

NC4 recommends the following: Check whether or not you are going to be affected. If you are running current versions of DNS software on your server(s), then you are unlikely to be affected by DNS Flag day unless you are also using load balancers and/or firewalls that are incompletely/incorrectly configured or that are unaware of current DNS protocol standards. You can check whether your domain will be affected by this change at https://dnsflagday.net. Test your domains to ensure that your services remain accessible after DNS flag day. If the tested domain fails the test, please contact your DNS operators. DNS server operators, please test your authoritative servers using the same link provided above. If the tested domain fails the test, please update your DNS software to the latest stable version and repeat the test. If they still fail even after the DNS software update please check your firewall configuration.

Verified Officially confirmed

National Cyber Coordination and Command Centre (NC4), NACSA would like to draw your attention on the DNS Flag Day 2019 which will be in effect starting from 1st February 2019.

First observed: 29 Jan 2019
Last checked: 31 Jul 2026
Evidence records: 1
Publication state: Published

What happened?

Current assessment

National Cyber Coordination and Command Centre (NC4), NACSA would like to draw your attention on the DNS Flag Day 2019 which will be in effect starting from 1st February 2019.

Why it matters

Slow access, service delivery interruptions, unreachable and intermittent availability.

Who is affected?

Affected products and groups

No affected entity has been safely confirmed in the structured record yet.

What should you do now?

Actions from official guidance

For technical teams

NC4 recommends the following: Official source
Check whether or not you are going to be affected. If you are running current versions of DNS software on your server(s), then you are unlikely to be affected by DNS Flag day unless you are also using load balancers and/or firewalls that are incompletely/incorrectly configured or that are unaware of current DNS protocol standards. You can check whether your domain will be affected by this change at https://dnsflagday.net. Test your domains to ensure that your services remain accessible after DNS flag day. If the tested domain fails the test, please contact your DNS operators. DNS server operators, please test your authoritative servers using the same link provided above. If the tested domain fails the test, please update your DNS software to the latest stable version and repeat the test. If they still fail even after the DNS software update please check your firewall configuration. Official source

Which sources support it?

Evidence and official sources

NACSA / NC4 Alerts and AdvisoriesOfficial source
DNS Flag Day 2019
National Cyber Coordination and Command Centre (NC4), NACSA would like to draw your attention on the DNS Flag Day 2019 which will be in effect starting from 1st February 2019.
Published 29 Jan 2019 · Retrieved 31 Jul 2026