Videos

OSI Model

Physical - 1s & 0s
Data Link - network protocols, error checking, frame sync. LLC & MAC
Network - IP, ICMP
Transport - TCP, UDP
Session - Communication channels between devices
Presentation - Defines how two devices should encode, encrypt, & compress data so it’s received correctly on both ends.
Application - Used by end user software. Provides protocols like HTTP, FTP, DNS, POP

Designed to overcome IPv4 shortages of addresses. The Router (NAT device) maintains a NAT table

Static NAT: maps 1:1 -> Private IP:Public IP
Dynamic NAT: many private IPs can share an equal or fewer amount of Public IP addresses
Port Address Translation aka overloading: most common in home networks. Allows for many Private IP addresses to one Public IP address. The NAT device records source IPs & ports, and replaces those with a single public IP, and a public source port, thus the name IP overloading

Classes:

A: 0.0.0.0 - 127.255.255.255
B: 128.0.0.0 - 191.255.255.255
C: 192.0.0.0 - 223.255.255.255
D: 224.0.0.0 - 239.255.255.255 - not allocated to hosts, used for multicasting
E: 240.0.0.0 - 255.255.255.255 - not available for general use. reserved for research purposes
Jack Rhysider subnet tool

192.168.0.15 is associated with the netmask 255.255.255.0 by using the CIDR notation of 192.168.0.15/24. This means that the first 24 bits of the IP address given are considered significant for the network routing. src

BK has a good resource on cryptography.
Practical networking - cryptography
There’s encryption at rest, and also in transit. the latter is what I’ll focus on
Good further reading, SSL & TLS

encrypts & decrypts using the same private key. this makes sense for encryption at rest
key exchange problem: one of the major drawbacks of Symmetric encryption is the Secret Key used to encrypt and decrypt must exist in two different locations. Which begs the question, how do we get the key securely from one party to the other?
with symmetric encryption, the algorithm is publicly known. the only variable between each encrypted conversation is the Secret Key.

uses public key & private key
The asymmetric keys are mathematically linked. What one key encrypts, only the other can decrypt — and vice versa.
I encrypt data with my recipient’s public key, I send it across the network, receiver decrypts with their mathematically linked private key (i.e the only key that can decrypt this message).
Message Signing is another advantage asymmetric encryption brings. read Using Asymmetric Keys for more insight
Compared to symmetric encryption, asymmetric is more expensive on resources

Usually carried out by a Botnet
Application Layer Attack: exploit the fact requests are cheap for clients, but computationally expensive for servers to deliver
Protocol Attack: aka SYN Floods. Botnet generates a huge number of spoofed SYN’s, and the server sends back SYN-ACK’s (to non-existent, spoofed IPs). The server then waits for ACK’s which will never happen
Volumetric/Amplification attack: similar to an application layer attack, exploits where a response is significantly larger than the request. Such as making spoofed requests to DNS

DNS root servers. 13 of these servers exist. managed independently.
IANA has info on the TLDs (.com, .au, .uk etc). Registries have more information about
- root zone -> name servers hosting the TLD zones. these TLD zones are run by registries that manage these TLDs -> name servers with the records for specific domains