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Iterative DNS Resolution Explained
When you type a domain name like www.example.com into your browser, the system needs to translate it into an IP address. One way this happens is through iterative resolution.
What is Iterative Resolution?
Iterative resolution means that the DNS resolver (usually your ISP’s DNS server) takes the responsibility of finding the IP address step by step. At each stage, a DNS server doesn’t fully resolve the query but instead returns a referral to another server that is closer to the answer.
It’s called iterative because the resolver repeatedly asks different servers until it gets the final answer.
How It Works — Step by Step
Let’s walk through an example for www.example.com:
- Client Request
Your computer asks the local DNS resolver (often your ISP’s resolver):
“What is the IP of www.example.com?” - Check Cache
If the answer is in cache, it’s returned immediately. If not, the resolver starts the iterative process. - Ask the Root Server
The resolver asks a root server forwww.example.com.- Root servers don’t know the IP of
www.example.com. - Instead, they reply with a referral to the
.comTLD servers.
- Root servers don’t know the IP of
- Ask the TLD Server
The resolver then asks a.comTLD server.- TLD servers don’t know the final IP either.
- They return a referral to the authoritative servers for
example.com.
- Ask the Authoritative Server
Finally, the resolver queries the authoritative server forexample.com.- This server returns the actual IP address of
www.example.com.
- This server returns the actual IP address of
- Return to Client
The resolver caches the answer for future queries and returns the IP address to your computer.
Iterative Resolution vs Recursive Resolution
- Iterative Resolution
- Each server only provides a referral to the next server.
- The resolver (e.g., ISP’s DNS server) does the heavy lifting.
- Reduces workload on higher-level servers.
- Recursive Resolution
- The resolver asks a server (e.g., Google Public DNS) to get the full answer.
- That server then performs the entire process on behalf of the client.
- Less work for the client, but more load on the resolver.
Pros of Iterative Resolution
✅ Distributes workload among servers
✅ Reduces traffic to root and TLD servers (since caching is used at each step)
✅ Faster response on repeated queries
Cons of Iterative Resolution
❌ Requires the resolver to handle multiple lookups
❌ Can be slower for a fresh query compared to recursive resolution
Simple Visualization
Client → Local Resolver
↓
Root Server → referral to .com
↓
TLD Server (.com) → referral to example.com
↓
Authoritative Server (example.com) → final IP
✅ In short: Iterative resolution is like following a map where each guide points you closer to the destination, but you have to do the walking yourself.
Would you like me to also create a diagram (visual graphic) for this, showing arrows from client → root → TLD → authoritative, so you can drop it into your blog post alongside this text?
