DNS request

Have you ever wondered what goes on behind the scenes when you visit a website like Google? How does your browser know where to find the web page you are looking for? How does it communicate with the server that hosts the website? How does it display the content on your screen?

In this blog post, I will explain the main steps involved in this process, from typing the URL in your browser to seeing the Google search page. I will focus on the following topics:

To do this, your browser makes a DNS request to a DNS server, which is like an address book for domain names. A domain name is a human-readable name for a website, such as google.com. A DNS server maps domain names to IP addresses, so that your browser can find the right server.

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TCP is responsible for ensuring reliable and ordered delivery of data packets between devices on the internet. It does this by dividing data into segments, adding sequence numbers and checksums to each segment, sending acknowledgments for received segments, and retransmitting lost or corrupted segments.

IP is responsible for routing data packets across different networks on the internet. It does this by adding source and destination IP addresses to each packet, and using routers to forward packets based on their addresses.

To establish a TCP connection, your browser and the server use a three-way handshake process:

After this handshake, your browser and the server have established a TCP connection and can exchange data.

For example, if you are using a home router, it may have a built-in firewall that blocks incoming traffic from unknown sources or outgoing traffic to certain ports or destinations. If you are using a corporate network, it may have more strict firewall rules that restrict what websites you can access or what applications you can use.

Firewalls can be configured to allow or deny traffic based on various criteria, such as IP addresses, ports, protocols, domains, applications, or content. Firewalls can also perform network address translation (NAT), which is a process of changing the source or destination IP address or port of a packet to enable communication between devices with different addressing schemes.

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The main purpose of HTTPS/SSL is to protect the confidentiality, integrity, and authenticity of the data exchanged between the browser and the server. Confidentiality means that only the intended parties can read the data. Integrity means that the data has not been modified in transit. Authenticity means that the parties can verify each other’s identity.

To achieve these goals, HTTPS/SSL uses a combination of symmetric encryption, asymmetric encryption, and digital signatures. Symmetric encryption uses the same key to encrypt and decrypt data, which is faster but requires a secure way to share the key. Asymmetric encryption uses a pair of keys: a public key that can be shared with anyone and a private key that must be kept secret. Data encrypted with one key can only be decrypted with the other key, which allows secure key exchange and authentication. Digital signatures use asymmetric encryption to generate and verify signatures that prove the origin and integrity of data.

To establish an HTTPS/SSL connection, your browser and the server use a handshake process similar to TCP:

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