DNS resolution
DNS answers the naming question: which resource records correspond to a domain name? A resolver may return an IPv4 address, IPv6 address, alias, mail server, or another record depending on the query.
DNS does not carry application traffic to the destination. It provides information that other networking layers can use.
IP routing
IP handles packet addressing and forwarding. Once an application has a usable destination address, routers and autonomous systems determine how packets reach the destination network.
Routing can change independently of DNS. A domain may keep the same name while its traffic moves between providers or networks.
How they interact
A typical web connection looks like this: the application resolves a hostname, receives an address, establishes a transport connection to that address, and then exchanges application data.
| Layer | Question answered |
|---|---|
| DNS | What address or record should this name resolve to? |
| IP | How should packets reach that destination address? |
| TLS / HTTP | How should the application session be secured and interpreted? |
Troubleshooting
When a service fails, separate DNS problems from routing and application problems. A correct DNS answer with unreachable routing is different from a stale DNS cache, and both differ from a server that is reachable but returns an application error.
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