关于多层网络资源域名DNS解析流程正确性及多级域名场景的问询

Great question! Let's break this down clearly, starting with verifying your initial understanding.

验证你的基本DNS解析流程 #

Your core understanding of how DNS resolves a domain like www.goodeggs.edu is almost perfect—there's just one small typo in step 4 (you wrote ".goodeggs.org" instead of ".goodeggs.edu") that we can fix. Let's recap the correct flow to confirm:

• Step 1: Your local device sends a DNS query for www.goodeggs.edu to your ISP's recursive DNS server, which doesn't have the IP cached.
• Step 2: Critical point you got right: DNS reads domain names from right to left (starting with the top-level domain, or TLD).
• Step 3: The ISP's server queries a root DNS server to find the TLD servers responsible for .edu. The root server returns the IP addresses of the .edu TLD servers.
• Step 4: The ISP server then queries the .edu TLD server to find the authoritative name servers for goodeggs.edu (not .goodeggs.org). The TLD server responds with the IPs of these authoritative name servers.
• Step 5: Finally, the ISP server queries the goodeggs.edu authoritative name server for the IP of www.goodeggs.edu. The authoritative server returns the IP, which the ISP forwards back to your local device.

Your summary of the ISP server's sequence is also correct, once we fix that typo: Root (for .edu) → .edu TLD → goodeggs.edu authoritative name server (where the final IP is retrieved).

关于多级域名（如www.bbc.co.uk）的解析流程 #

Your thinking is on the right track, but let's clarify the terminology and exact flow—DNS doesn't have "TLD1" or "TLD2" levels. Here's how it works for a domain like www.bbc.co.uk:

1. The ISP's recursive server starts by querying a root DNS server to find the TLD servers for .uk (this is the only true TLD here).
2. The root server returns the IPs of the .uk TLD servers.
3. The ISP server queries the .uk TLD server to find the authoritative name servers for co.uk (this is a second-level domain under .uk).
4. The .uk TLD server responds with the IPs of the co.uk authoritative servers.
5. Next, the ISP server queries the co.uk authoritative servers to find the authoritative name servers for bbc.co.uk (a third-level domain).
6. The co.uk servers return the IPs of the bbc.co.uk authoritative name servers.
7. Finally, the ISP server queries the bbc.co.uk authoritative servers for the IP of www.bbc.co.uk, which is then sent back to your device.

To simplify the sequence: Root (for .uk) → .uk TLD → co.uk authoritative server → bbc.co.uk authoritative server (where the final IP is retrieved).

The key takeaway is that each level after the TLD is just another authoritative domain server—there's only one TLD per domain (.uk in this case), and the rest are subdomain authoritative servers.

内容的提问来源于stack exchange，提问作者Clive Long