Think it through together · A little story
A girl visits a domain name for the first time. The robot cannot find a usable record locally, so it asks a resolver to keep looking.
Lay out the process
- Check the cache firstIs there a record that is still valid?
- Ask a resolverHelp find the record
- Get a recordReturn an address
- Visit the websiteSet up the next connection
A DNS lookup often starts with an existing cache. If a record is missing, a recursive resolver continues looking for it.
It can follow the domain-name hierarchy to find the server responsible for the name. After getting the record, it returns it. Cached records have an expiration time; an old address cannot be used forever.
Different devices and networks may have different caching steps. This diagram shows the main idea.
Your turn to try
Why might a second visit to a domain name you just looked up take fewer steps?
Have you thought it through? Open for an explanation
A valid cached record may already be available, so it can be used directly without repeating the entire lookup.
Take away one discovery
A DNS lookup often starts with an existing cache. If a record is missing, a recursive resolver continues looking for it.
Try covering the diagram above and explaining each step to someone in your family. If one step is hard to explain, go back and look at that card again.