OSI model
- physical, data link, network, transport, session, presentation, application
- encapsulation
- Five layers in Internet: physical, data link, network, transport, application (including presentation and session layers of OSI model),
TCP/IP sits in kernel of operating system. packet is passed from RAM to the network card, then through the ethernet cable.
There is a specific bus for tcp/ip between ram and NIC 
^ Data link and physical layer.
NIC rejects ehternet packets which aren’t adresse to them. you can modify them to add a promoscuous mode which accepts all packets.
you can configure the swtich to send the packets to only the correct address
Network Layer ≡ IP layer
Port number distinguishes addresses at the transport/application layer.
ARP - to find destination MAC address given IP address
- send broadcast message to everyone - who had this IP address? What is your MAC address
- the store the results of the MAC:IP pairing
sudo arp -alist arp pairings
Journey of IP packet. 
routing table created - manual or dynamic. DNS, etc
TCP IP moves the data - there are more protocols within the TCP IP layer that help it to work better.
Questions
- what is a gateway
- connected to the same LAN
- when ip is created it will check this table
- LAN can have more that one gateway