132 lines
5.2 KiB
Markdown
132 lines
5.2 KiB
Markdown
# So You Want to Make Internet Lasagna?
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## The Recipe
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| Communication | Discovery |
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| ------------- | --------- |
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| HTTP | DNS |
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| TCP | |
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| IP | DHCP |
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| Ethernet | ARP |
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<br>
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## Starting from HTTP
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HTTP (Hypertext Transfer Protocol), is what browsers use talk to web servers to send and receive web pages,
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do basic transactions, like sending a form from your browser to the server, requesting some database
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information for display, or updating your account settings.
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Good learning resources for HTTP:
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- https://developer.mozilla.org/en-US/docs/Web/HTTP/Overview
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- https://developer.mozilla.org/en-US/docs/Web/HTTP/Messages#http_requests
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<-- Link to expanded, less curated library of topical info -->
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<-- Branch into REST/GraphQL here -->
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## Diving into the meat and potatoes with TCP and IP
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HTTP responses and requests are a sequence of bytes, chunked up and sent in packets,
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often through a protocol called TCP (Transmission Control Protocol). TCP provides a few
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nice guarantees which make writing reliable network code a little easier.
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When a message gets sent via TCP, it ensures that chunks get passed to the application
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in order. If packets get dropped along the way, or arrive out of order, TCP handles resending
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missed packets and buffering before the application gets the packet, until order can be restored.
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Good learning resources for TCP:
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- https://www.youtube.com/watch?v=4IMc3CaMhyY
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- https://www.youtube.com/watch?v=F27PLin3TV0
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- https://www.youtube.com/watch?v=IP-rGJKSZ3s
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<-- Link to expanded, less curated library of topical info -->
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<-- Branch into UDP, QUIC, TLS, etc. via link here -->
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IP (Internet Protocol) sits directly below TCP, but often gets bundled together. IP is a
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small header attached right above the protocol header, and contains important information,
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like where the packet is coming from, and where the packet needs to go, so network hardware
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along the way can route it from A->B to reach it's destination
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Good learning resources for IP:
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- https://www.youtube.com/watch?v=rPoalUa4m8E
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- https://www.youtube.com/watch?v=VWJ8GmYnjTs
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<-- Link to expanded, less curated library of topical info -->
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<-- Branch into TUN via link here -->
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<br>
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## Making it Tractable
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So, how do you take all that theory and make it stick? How do you send a real packet yourself?
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Some good outlets for exercises:
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- https://beej.us/guide/bgnet/html/
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- https://github.com/shuveb/zerohttpd
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## Taking the Real Plunge
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Ok, so you've got some of the basics down, and you're ready for some serious spelunking?
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Let's talk Ethernet and PHY.
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- https://www.youtube.com/watch?v=XaGXPObx2Gs&list=PLowKtXNTBypH19whXTVoG3oKSuOcw_XeW
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<br>
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## Buttoning up with Discovery Protocols
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So, how does the computer get an IP address? How do we know what the router's IP is?
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How do find the IP address of "https://handmade.network/" so we can send it a request?
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Discovery protocols to the rescue!
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## Putting on the ARP Goggles
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At the bottom of the protocol stack, ARP (Address Resolution Protocol) is how your computer
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reaches out and understands the local network it lives on. When an ethernet cable gets plugged into
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your computer, it broadcasts an ARP packet, gathering responses to know how to address
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messages directly to specific local machines. The initial ARP packet contains the MAC
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address of the computer sending, and responses from all machines that want to be discovered
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get fired back with their MAC addresses in tow.
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Good learning resources for ARP:
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- https://www.saminiir.com/lets-code-tcp-ip-stack-1-ethernet-arp/
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<-- Link to expanded, less curated library of topical info -->
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<-- Branch into TAP via link here -->
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## Finding the Mailman with DHCP
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DHCP sits near the middle, but is incredibly important. When you want to send a packet to a network
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beyond your own, somebody has to deliver that packet. To find the packet post office, your computer
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broadcasts a DHCP discover packet, and collects IP offers from all DHCP servers on the network.
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At that point, typically it will fire off a request for the first IP it recieves, and get a
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confirmation or denial for that request. DHCP acks typically also contain the IP address of the router,
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the local DNS server, and more
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Good learning resources for DHCP:
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- https://docs.microsoft.com/en-us/windows-server/networking/technologies/dhcp/dhcp-top
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<-- Link to expanded, less curated library of topical info -->
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<-- Branch into PXE Booting via link here -->
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## Using the DNS Phonebook
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DNS sits at the top acting as a final, important, icing on the cake. The job of DNS is primarily to
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provide lookup services for domain names. To resolve "https://handmade.network/" into an IP address
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so we can send it an HTTP request, we send a lookup request to the DNS server, and it will do the requisite
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forwarding until it either has an IP address to send back, or fails.
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Good learning resources for DNS:
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- https://www.cloudflare.com/learning/dns/what-is-dns/
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<-- Link to expanded, less curated library of topical info -->
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<-- Branch into DNS over HTTPS / DNS Lookup Security via link here -->
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## Fun Tangents
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- Network Bridging
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- DHCP Robin Hood
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- PXE Booting
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- SMTP
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- Routing and Switching
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- BGP
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- TLS/SSL
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- Inspection and Testing Tools: tcpdump, wireshark, netcat and more
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