Entitites

host: any device that sends or receives traffic
- client: requests
- server: receives requests and returns data
  - any computer with server software
IP address: ID for hosts
- included in every packet as src and dst
- IPv4: 32 bits, 4 octets -> decimal number
- hiearchical
  - example of country: first number can denote country branch, second number can denote division, third number can denote conference room, etc…
network: transports traffic between hosts
- logical grouping of hosts, like house, cafe, classroom, etc…
- can have subnets
- networks <-> networks via Internet

Devices

repeater: takes signal and amplifies it
p2p connection doesn’t work -> hub: multi-port repeater connecting many hosts
- central node in graph, everyone connected to host
- everyone receives all data
- to separate groups of hosts, we need
bridge: 2-port device connecting 2 hubs
- know which hosts are in which side -> only lets packets to other hub when necessary
switches: combination of hub and bridge
- learns which hosts on each port -> communication within network
- switching: moving data within networks
router: communication between networks
- traffic control point at center of networks -> good for filtering, security, etc…
- learns which network are attached, aka routes
- has IP address in every attached network, acts as gateway
  - example: laptop in one classroom’s (A) switch is connected to router. To send traffic to another laptop in another classroom (B), packet goes from laptop -> switch -> router (gateway in A) -> router (gateway in B) -> switch -> laptop
- routing: moving data between networks