DNS Refresh Rate: How Often It Updates

DNS records refresh at intervals set by each domain’s TTL (Time to Live), commonly 300 to 3600 seconds (5 minutes to 1 hour), but the practical wait for a change to appear everywhere is usually a few hours. The exact time depends on the TTL you set, the caching behavior of recursive resolvers (like your ISP or Google Public DNS), and the DNS record type.

What Is DNS TTL?

TTL is a number, in seconds, that a DNS resolver is allowed to keep a record in its cache before asking the authoritative server again. When you query a domain, the response includes a TTL for each record. The resolver stores that record and the TTL counts down. Once it reaches zero, the resolver discards it and performs a fresh lookup. This mechanism balances speed (cached answers are fast) with freshness (records eventually update).

For example, a TTL of 3600 means a resolver may reuse the same IP address for up to one hour. If you change that IP, some users may still reach the old address for up to an hour. The TTL is set by the domain owner at the authoritative DNS server, not by the resolver.

How DNS Propagation Actually Works

When you update a DNS record (say, changing the A record of example.com from 192.0.2.1 to 192.0.2.2), the change is instant at the authoritative server. But the internet doesn’t query that server every time. Instead, recursive resolvers cache answers. The chain looks like this:

• Your device (laptop, phone) asks its configured recursive resolver (often your ISP or a public resolver like 8.8.8.8).
• That resolver, if it has no cached answer, queries the root server, then the TLD server, then the authoritative server for the domain.
• The authoritative server returns the answer with a TTL. The resolver stores it and serves it to any client that asks until the TTL expires.
• Each resolver has its own cache, so propagation is not a single event but a gradual process as each resolver’s TTL expires.

Because there are thousands of resolvers worldwide, each with its own cache state, a change can take from minutes to 48 hours to fully propagate, though 24–48 hours is the old rule of thumb. In practice, most resolvers respect TTLs, so if you set a low TTL before the change, propagation is faster.

How to Choose a TTL

There’s no universal “best” TTL; it depends on how often you change records and how much traffic you get. Consider these factors:

• Stability: If your IP rarely changes, a longer TTL (e.g., 86400) reduces DNS queries and improves performance slightly.
• Planned changes: If you expect to update records soon, lower the TTL to 300 (5 minutes) a day or two before the change, then raise it back after.
• Failover needs: If you rely on DNS-based failover (e.g., switching to a backup server), a low TTL (60–300) ensures faster recovery but increases query load.
• Traffic volume: High-traffic sites benefit from longer TTLs because fewer queries hit the authoritative server, but the trade-off is slower updates.

Many domain registrars default to 3600 (1 hour) or 14400 (4 hours). For most websites, 300–3600 is a sensible range. For critical services, 60–300 might be appropriate.

Common Problems and Misconceptions

One common myth is that DNS changes are “propagating” as if they travel across the internet like a wave. In reality, there’s no central propagation; each resolver independently decides when to refresh. Another misconception is that flushing your local DNS cache (e.g., ipconfig /flushdns on Windows) updates the internet. It only clears your device’s cache; it doesn’t affect other resolvers.

Another issue: some resolvers ignore TTLs and cache longer than instructed (often for negative answers or due to misconfiguration). This can cause delays beyond the TTL. Also, some hosting providers have a “minimum TTL” enforced on their nameservers, so you can’t set a TTL lower than, say, 30 seconds. Check your DNS provider’s documentation.

DNS Record Types and Refresh Differences

Not all records behave the same. A records and AAAA records (IP addresses) are what most people think of. But other types have their own caching quirks:

• MX records (mail servers) often have longer TTLs (e.g., 3600) because email servers may cache them aggressively.
• NS records (nameservers) are cached by TLD servers and often have TTLs of 172800 (2 days) or more. Changing nameservers can take 24–48 hours.
• CNAME records (aliases) follow the same TTL rules, but the target’s TTL also matters.
• TXT records (SPF, DKIM, verification) are usually short-lived, but some services recommend 3600.

For email, a low TTL on MX records can help if you plan to switch mail providers, but be aware that some mail servers ignore TTLs and cache for days.

How to Check Propagation Status

To see if a change has taken effect, you can query public DNS resolvers directly. Many free online tools (like whatsmydns.net or dnschecker.org) query multiple resolvers and show which ones have the new record. Alternatively, use the command line:

1. On Windows: nslookup -type=A example.com 8.8.8.8
2. On macOS/Linux: dig @8.8.8.8 example.com A

Replace 8.8.8.8 with any resolver IP (e.g., 1.1.1.1 for Cloudflare). The response includes a TTL value; if it’s high, the resolver cached it recently. You can also check the authoritative server directly (using the nameserver from dig NS example.com) to confirm the record is correct there.

Frequently Asked Questions

Why is my DNS change not showing after 24 hours?

Several reasons: the TTL may be long (e.g., 86400), some resolvers ignore TTLs, or you’re checking a resolver that hasn’t refreshed. Also, if you changed nameservers (NS records), the TLD servers may cache the old ones for up to 48 hours. Check the authoritative server first to ensure the record is correct, then query a few public resolvers.

Does lowering TTL speed up propagation?

Yes, but only if you lower it before making the change. If you lower the TTL to 300, existing caches will expire within 5 minutes (assuming they honor it). Then, when you update the record, the new value will be fetched quickly. If you lower it after the change, you still have to wait for the old TTL to expire.

What is the default TTL for most domains?

There’s no universal default, but common values are 3600 (1 hour), 14400 (4 hours), and 86400 (1 day). Many registrars and DNS hosts set 3600 by default. For cloud services like AWS Route 53, the default is 300 for some record types.

Can I set TTL to 0?

Technically, a TTL of 0 means the record should not be cached at all, and every query goes to the authoritative server. This is rarely used because it increases load and latency. Some DNS providers allow it, but it’s not recommended for production. For testing, it can be useful, but be prepared for slower responses.

How long does it take for a new domain to start resolving?

When you register a new domain and add DNS records, it can take from a few minutes to a few hours for the TLD servers to recognize the nameservers. Once that happens, resolvers can fetch the records. Usually, it’s under an hour, but in rare cases, it can take up to 48 hours.

Why do some websites update instantly while others take days?

It depends on the TTL and the resolver. If a website has a low TTL (e.g., 60 seconds) and you query a resolver that respects it, you’ll see the change within a minute. But if the resolver has cached the old record with a long TTL, it will keep serving it until expiry. Also, some ISPs have non-standard caching that ignores TTLs, causing delays.

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in ttl | TTL value | seconds | 3600 | 60 | 86400
in c | Number of caches | - | 3 | 1 | 20
out total | Total propagation estimate | hours | (ttl * c) / 3600 | 2