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Enhanced DNS lookup section with caching and resolver details #2513

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22 changes: 8 additions & 14 deletions README.rst
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Expand Up @@ -209,20 +209,14 @@ Check HSTS list
DNS lookup
----------

* Browser checks if the domain is in its cache. (to see the DNS Cache in
Chrome, go to `chrome://net-internals/#dns <chrome://net-internals/#dns>`_).
* If not found, the browser calls ``gethostbyname`` library function (varies by
OS) to do the lookup.
* ``gethostbyname`` checks if the hostname can be resolved by reference in the
local ``hosts`` file (whose location `varies by OS`_) before trying to
resolve the hostname through DNS.
* If ``gethostbyname`` does not have it cached nor can find it in the ``hosts``
file then it makes a request to the DNS server configured in the network
stack. This is typically the local router or the ISP's caching DNS server.
* If the DNS server is on the same subnet the network library follows the
``ARP process`` below for the DNS server.
* If the DNS server is on a different subnet, the network library follows
the ``ARP process`` below for the default gateway IP.
* The browser first checks its local **DNS cache** to see if it already knows the IP address.
* If not found, it checks the **operating system’s DNS cache**.
* If still unresolved, it sends a request to the **configured DNS resolver** (often an ISP’s DNS server).
* The resolver may return a cached response or forward the request to **root DNS servers**.
* The process continues until it reaches an **authoritative DNS server** that provides the correct IP address.
* A `dig` command can demonstrate this process:
```bash
dig google.com


ARP process
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