<aside> 📖 Properties

• Datagram
  • Individually routed packets. Hop-by-hop routing.
  • Header = IPDA (IP dest. addr) + IPSA (IP src. addr.)
• Unreliable
  • Packets might be dropped.
• Best effort
  • Make promise to only drop datagrams if necessary
• Connectionless
  • No per-flow state.
  • Packets might be mis-sequenced. </aside>

<aside> 📖 Why is the IP service so simple?

• Simple, dumb, minimal
  • Faster, more streamlined and lower cost to build and maintain.
• The end-to-end principle
  • Where possinle, implement features in the end hosts
• Allow a variety of reliable (or unreliable) services to be built on top
  • Let the applications choose their own reliability
• Works over any link layer
  • IP makes very few assumptions about the link layer below </aside>

<aside> 📖 More details

1. Tries to prevent packets looping forever
   • Time to Live (TTL) field, to detect loops
2. Will fragment packets if they are too long
3. Uses a header to checksum to reduce chances of delivering datagram to wrong destination
4. Allows for new versions of IP
   • IPv4 32 bit, IPv6 128 bit

IPv4 Datagram

</aside>