net_request_full_breakdown - dwilson2547/wiki_demo GitHub Wiki

• Network Request Full Breakdown
• 1. User Initiates a Request
• 2. DNS Lookup Process
  • 2.1. Local DNS Cache Check
  • 2.2. Recursive DNS Query
  • 2.3. Iterative DNS Query
  • 2.4. Caching the Result
• 3. Establishing a Connection
  • 3.1. TCP/IP Handshake (TCP)
  • 3.2. TLS Handshake (HTTPS)
• 4. Routing the Request
  • 4.1. Local Network Routing
  • 4.2. Router’s Role
  • 4.3. ISP and Internet Routing
  • 4.4. Destination Network
• 5. Server Processing the Request
  • 5.1. Web Server
  • 5.2. Sending the Response
• 6. Return Trip: Response to Your Device
  • 6.1. Internet Routing (Reverse Path)
  • 6.2. Your ISP’s Gateway
  • 6.3. Your Router
  • 6.4. Your Device
• 7. Connection Termination
• 8. Summary of Devices and Protocols Involved
• 9. Example Timeline

• Example: You type https://www.example.com into your browser and press Enter.
• Browser Role: The browser checks its cache for a valid IP address for www.example.com. If not found, it initiates a DNS lookup.

• Browser Cache: The browser checks its internal DNS cache.
• OS Cache: If not found, the OS (e.g., Windows, macOS, Linux) checks its DNS cache.
• Router Cache: If still not found, the request is sent to the local router (default gateway), which may also cache DNS records.

• Local DNS Resolver: If the IP isn’t cached, your device sends a recursive DNS query to your configured DNS resolver (e.g., your ISP’s DNS server or a public DNS like Google’s 8.8.8.8).
• Resolver’s Role: The resolver checks its cache. If the IP isn’t cached, it initiates an iterative DNS query.

1. Root DNS Servers:

   • The resolver queries a root DNS server (e.g., a.root-servers.net).
   • The root server responds with the TLD (Top-Level Domain) DNS server for .com (e.g., a.gtld-servers.net).

2. TLD DNS Servers:

   • The resolver queries the .com TLD server.
   • The TLD server responds with the authoritative DNS server for example.com (e.g., ns1.example-dns.com).

3. Authoritative DNS Servers:

   • The resolver queries the authoritative server for example.com.
   • The authoritative server responds with the IP address for www.example.com (e.g., 93.184.216.34).

• The resolver caches the IP address and returns it to your device.
• Your device caches the IP address for future use.

• Your device initiates a TCP connection to the IP address (93.184.216.34) on port 443 (HTTPS).
• Three-Way Handshake:
  1. SYN: Your device sends a SYN (synchronize) packet to the server.
  2. SYN-ACK: The server responds with a SYN-ACK (synchronize-acknowledge) packet.
  3. ACK: Your device sends an ACK (acknowledge) packet, and the connection is established.

• If the URL uses https://, a TLS handshake occurs to establish a secure, encrypted connection:
  1. Client Hello: Your device sends supported TLS versions and cipher suites.
  2. Server Hello: The server selects a TLS version and cipher suite and sends its SSL certificate.
  3. Certificate Verification: Your device verifies the certificate with a Certificate Authority (CA).
  4. Key Exchange: Your device and the server generate a shared secret key for encryption.
  5. Encrypted Communication: All further communication is encrypted using the shared key.

• Your Device: Uses its routing table to determine the next hop for the packet. For most home networks, the next hop is the default gateway (your router).

• ARP (Address Resolution Protocol):

  • Your device checks its ARP cache for the MAC address of the default gateway.
  • If not found, it sends an ARP request (broadcast) to discover the MAC address of the router.
  • The router responds with its MAC address, and your device updates its ARP cache.

• Packet Forwarding:

  • Your device encapsulates the packet with:
    • Source MAC: Your device’s MAC address.
    • Destination MAC: Router’s MAC address.
    • Source IP: Your device’s private IP (e.g., 192.168.1.10).
    • Destination IP: 93.184.216.34 (example.com’s IP).
  • The packet is sent to the router.

• NAT (Network Address Translation):

  • The router replaces the source IP in the packet header with its public IP (e.g., 203.0.113.5).
  • It assigns a source port (e.g., 54321) to track the connection and adds an entry to its NAT table.
  • The packet now has:
    • Source IP: 203.0.113.5 (router’s public IP).
    • Source Port: 54321.
    • Destination IP: 93.184.216.34.
    • Destination Port: 443.

• Routing Decision:

  • The router checks its routing table to determine the next hop for 93.184.216.34.
  • If the destination is on the internet, the router forwards the packet to your ISP’s gateway.

• ISP’s Gateway:

  • Your ISP’s router receives the packet and checks its routing table.
  • It forwards the packet to the next hop in the internet backbone, based on BGP (Border Gateway Protocol) routes.

• Internet Backbone:

  • The packet traverses multiple autonomous systems (AS) and routers along the path to 93.184.216.34.
  • Each router along the path:
    1. Receives the packet.
    2. Checks its routing table (populated by BGP, OSPF, or other routing protocols).
    3. Decrements the TTL (Time To Live) field in the IP header.
    4. Forwards the packet to the next hop.

• Edge Router:

  • The packet arrives at the edge router of example.com’s network.
  • The router checks its routing table and forwards the packet to the internal router or load balancer handling 93.184.216.34.

• Firewall/Load Balancer:

  • The packet passes through a firewall, which checks for security rules (e.g., allowed ports, DDoS protection).
  • If example.com uses a load balancer, the packet is forwarded to an available web server.

• The web server receives the packet on port 443.
• The server:
  1. Decrypts the TLS-encrypted data.
  2. Processes the HTTP request (e.g., GET /).
  3. Generates an HTTP response (e.g., the HTML for the homepage).

• The server sends the response back to your device:
  • Source IP: 93.184.216.34.
  • Destination IP: 203.0.113.5 (your router’s public IP).
  • Source Port: 443.
  • Destination Port: 54321.

• The response packet traverses the internet back to your ISP, following the reverse path of the original request.
• Routers along the path use their routing tables to forward the packet toward 203.0.113.5.

• Your ISP’s router forwards the packet to your home router.

• NAT Translation:
  • The router checks its NAT table and finds the entry for 203.0.113.5:54321.
  • It replaces the destination IP and port with your device’s private IP and original port (e.g., 192.168.1.10:12345).
• ARP Check:
  • The router checks its ARP cache for your device’s MAC address.
  • If not found, it sends an ARP request to discover your device’s MAC address.
• Packet Forwarding:
  • The router encapsulates the packet with:
    • Source MAC: Router’s MAC address.
    • Destination MAC: Your device’s MAC address.
  • The packet is sent to your device.

• Your device receives the packet and:
  1. Decrypts the TLS data (if HTTPS).
  2. Processes the HTTP response (e.g., renders the webpage).
  3. Displays the webpage in your browser.

• After the response is received, the TCP connection is terminated using a four-way handshake:
  1. FIN: Your device sends a FIN (finish) packet.
  2. ACK: The server acknowledges the FIN.
  3. FIN: The server sends its own FIN packet.
  4. ACK: Your device acknowledges the server’s FIN, and the connection is closed.

1. You enter `https://www.example.com` in your browser.
2. Browser checks DNS cache → OS checks DNS cache → Router checks DNS cache.
3. Recursive DNS query to ISP’s resolver → Iterative queries to root → TLD → authoritative DNS.
4. ISP’s resolver returns `93.184.216.34`.
5. Your device initiates TCP handshake with `93.184.216.34:443`.
6. TLS handshake establishes encryption.
7. Packet routed: Your device → Router (NAT) → ISP → Internet → Example.com’s edge router → Load balancer → Web server.
8. Server processes request and sends response.
9. Response routed back: Web server → Load balancer → Internet → ISP → Router (NAT) → Your device.
10. Browser renders the webpage.

This process happens in milliseconds for well-optimized networks! Let me know if you'd like to dive deeper into any specific step.