Networking Overview

TODO:

this page is abysmal. fix.

Resources

router overview

https://www.uhcl.edu/computing/information-security/tips-best-practices/routers

Tutorials

code a TCP/IP stack

https://www.saminiir.com/lets-code-tcp-ip-stack-1-ethernet-arp/

5-layer TCP/IP model

-	layer	protocol	unit	address
1	physical	10 Base T, 802.11	Bits	n/a
2	datalink	Ethernet, WiFi	Frames	MAC addr
3	network	IP	Datagram	IP addr
4	transport	TCP, UDP	Segment	Ports
5	application	HTTP, SMTP, ..	Messages	n/a

Example Transaction

TODO:

this takes a lot of space, and is not very helpful. Find a better way to describe this.

An example might help this sink in.

visit a website: #(GET request on server's port 80)

transport (HTTP)
   request is sliced into segments(transport) of 536 bytes or smaller

network (TCP/IP)
   if network knows how to reach destination, each segment is wrapped in
   TCP/IP info, and handed off to the datalink layer.

datalink (MAC,ARP)
   Adds information about the physical protocol (ethernet, token-ring, ...) 
   and fires the data to a target MAC address.

---

physical
   the information is sent over the wire

--- 

On the receiving end, datalink, and network layers are stripped off, and all 
segments (transport) are re-assembled to form the request. This is handed to
the web-server, which then repeats the above with a reply.

Layers

Physical

coax

optical

Datalink

protocols
ethernet	most commonly used protocol for the datalink layer

terminology
routing schemes	broadcast, unicast, multicast, ...
duplex	If traffic can be sent/received at the same time
MTU	the largest allowed frame-size (datalink) on a network.

Network Configurations
vlan	using one NIC/cord to share multiple connections to separate networks (ex: WAN/LAN on firewall)

Datalink Errors
frame errors	Frames received with an invalid checksum.
drops	Frames that were discarded by the netwk iface. unexpected VLAN tags, ipv6 packets when iface is not configured for ipv6.
overruns	Too much data received too quickly (before kernel can handle them). The buffer is full, so packets are dropped.
collisions	On half-duplex netwk, when 2x sides of a connection are talking at the same time.

finding datalink errors

netstat -i

## Windows does not officially support viewing datalink errors. check the switch

TX-     ## packets sent
RX-     ## packets received


*-OK   ## correctly recceived frames
*-ERR  ## incorrect packets received
*-DRP  ## packets dropped at this interface
*-OVR  ## packets this interface was unable to receive

Network

Protocols
ipv4
ipv6

Transport

Protocols
tcp