For Full Details, see [SingCERT] Alert on DNS Flag Day
Domain Name System (DNS) infrastructure operators and Internet service providers are taking part in the first DNS Flag Day  on 1 February 2019. This is a global initiative to promote the use of Extension Mechanism Protocol for DNS (EDNS)  where participants, software and service providers such as Google and Cloudflare, are going to remove non-standard DNS workarounds.
Authoritative nameservers that bypass and do not support the EDNS protocol and those with proprietary implementations of the DNS protocol, e.g. legacy load balancing appliances.
Internet users might experience slowness or inaccessibility issues when interacting with domains whose authoritative nameservers are affected, such as accessing websites or sending emails.