Summary: 1 computer on it’s own is nothing compared to what a bunch of computers can do when they put their minds together!
** housekeeping – last episode meant to cover NX bits and semaphores
Kids analogy: first 3 months are just selfish getting to know how the body works. Then notice that there are others around that come and go, but world still revolves around self. peekaboo is eternally funny because no sense of time or predictability. Then recognition of key people in life and recognition of dependence on interaction. Mobility shows that people exist outside of site and have their own lives to live. Maybe the kid discovers that there are other people that share his / her name, and mind is blown that they are not as unique as they thought. Then stranger danger feelings start coming out, but they are surrounded by trustworthy people, and that feeling goes away. Then they meet people with their own agenda and get what they want by taking advantage of this trust. Not that I’m bitter or anything….
Sharing files pre-network (a.k.a. sneaker-net): floppy disks -> thumb drives. computers of the day come with the mechanism and built into the OS.
Special hardware for networking in computers like modems and network cards. Required physical connection e.g. fiber-optic or twisted pair ethernet , or now can be over the airwaves. Also requires protocols in which to communicate
Define protocol: The established code of procedure or behaviour (in any group, organization, or situation). Think phone call
Topology means way in which parts are laid out and connect.
Bus: like a school bus; seats and alleyway, but pretend the only way to speak is over a megaphone. Token ring and FDDI (fiber distributed data interface) still common in some settings
Ring: like passing notes in class if desks were set up in a square and could only pass to the right
Star: like the telephone system where pretend each house is tied into a single CO. Ethernet is pretty much ubiquitous now, be it attached via a cable to the back of your computer or WiFi
protocols are vetted and approved by the IETF through their RFCs
deep dive into Ethernet: It’s just a transportation medium like a money vaccuum tube at a grocery store.
Carrier Sense Multiple Access / Collision Detection looks both ways before crossing the street. If pedestrian dies wait a random time before sending another one onto the crosswalk.
MAC address burnt into chip and defined as 6 bytes represented in hexidecimal pairs seperated by collons. They are the way neighbours talk to each other, and are supposed to be unique. First half is manufacturer code, second half is “unique” number
Pre-amble is a “listen up, new frame”
destination MAC address
Source MAC address
Ethernet type / length of data segment
data segment (payload)min 64 bytes(runt) to 1500 bytes (jumbo)
gloss over of IP (limiting to LAN):
IP address is a unique 4 byte number usually represented by 4 clusters of up 3 decimal numbers, ranging from 0 to 255. E.g. 192.168.1.21
IP addresses need to be unique within the same broadcast domain, e.g. an office or home
Packet structure is more complex then ethernet frame but has things like version number, source address, destination address, and payload. More on this next episode.
The way that we bridge the IP address to the MAC address is a type of ethernet payload called Address Resolution Protocol. It broadcasts a message across the ethernet and asks “who has IP address x?” and then the person with IP address x replies “I do!” The source MAC address of each the messages are remembered in an ARP lookup table of all participants.
2 attacks exploiting ARP:
ARP cache poisoning:
– pre-populate mac addresses in tables by sending “I do” answers before the question is ever asked. Good way to become the man in the middle
– constant flood of “I do!” replies is a way to overload a switch and turn it into hub mode, allowing to eavesdropping.
Internet Engineering Task Force – Request for Comments