DNS Propagation is the time it takes for recent changes to your domain's DNS records to be updated across all the DNS servers on the internet. Because the internet is massive, DNS records are temporarily saved (cached) by local servers to speed things up. Updating those cached records globally takes time.
Did you just migrate your website? Check if your new DNS records are active worldwide.
To understand propagation, you need to understand TTL (Time to Live). Every DNS record has a TTL value, usually set in seconds (e.g., 3600 seconds = 1 hour). When an Internet Service Provider (like Comcast or Vodafone) looks up your website, they save the IP address in their local memory for the duration of that TTL.
If you change your DNS record at your web host, that local ISP doesn't know about it. They will keep sending visitors to your old IP address until their 1-hour timer runs out. Only then will they ask your host for the new records. This delay is what we call propagation.
No. This is a very common misconception. Lowering your TTL only affects future lookups. If a resolver has already cached your record with a 24-hour TTL, changing your TTL to 5 minutes right now won't force them to flush their cache. You must lower your TTL before you plan to make a migration (preferably a day in advance).
Usually, standard records (like A, CNAME, or TXT) propagate within a few hours. However, changing your Nameservers (NS records) is a different story. NS records are cached by the Top Level Domain (TLD) registries (like .com or .org), which often enforce a hard 48-hour cache. If you change Nameservers, you should expect up to two days of mixed traffic.
Different internet users query your domain at different times. If User A visited your site 5 minutes before your DNS change, their ISP caches the old record. If User B visits your site right after the change (and their ISP's cache was empty), they will get the new record. This results in global resolvers showing mixed answers until all caches expire.