networks.txt

Networks:
OSI 7 layer model
- Physical, Fiber optics/hardware to transmit bits
- Data Link, Connecting data to hardware, MAC addressing in routers, multiplexing error checking
- Network, world-wide addressing of devices -- IP addresses
- Transport, packetization and ordering of data -- TCP/UDP
- Session, opening and closing of connected sessions -- TCP/UDP
- Presentation, serialization/deserialization of data for consumption
- Application set of api's to communicate across networks

Public and private IP's
- Private IP addresses: start with 192.168.xxx.xxx or 10.xxx.xxx.xxx
- Private IP addresses are behind routers. used on local area networks
- Your router has your public ip address

IPv4 vs IPv6
- IPv4 uses 32 bits for addresses
- IPv6 uses 128 bits for addresses

TCP vs UDP
- UDP is more primitive, does not guarantee order or that packets are received
- TCP is UDP wrapped in some stuff to make sure packets are received in an ordered manner
- TCP is used in HTTP, FTP and Telnet
- Client ------> Syn ------> Server
-        <---- Syn/Ack <----- 
-        -------> Ack ------>
- MAC addresses (Media Access Control) are hardwired to Network Interface Card (NIC)
- used to identify devices, can be used as address in LAN
- At lower levels of Ethernet, everything is translated to MAC addresses via ARP (Address Resolution Protocol) can be hacked

Addressing
- All IP addresses are composed of network and host sections
- Calculate network and host sections witho IP address + Subnet Mask and bitwise AND operator.
- in IPv6 Calculate with number after the slash as number of bits in network section
- Network section = network address. Host section = host address within a given network

DHCP (Dynamic Host Configuration Protocol)
- vs. static assignment... Assign host IPs in a given network
- Clients search/connect to a DHCP, query and are assigned a host ip on the network
- Sometimes DHCP will have a default name server for routing
- DHCP can be spoofed to serve bad names

Classful networks vs Classless Inter-Domain Routing (CIDR)
- Classful -> IPv4 replaced with CIDR in 1993
- has variable length subnet masking and CIDR notation.
- Address is suffixed with the number of bits in the prefix (instead of subnet mask?)
- variable length subnet masking allows networks to be sized appropriately according to needs (based on available host ip address space?)