This post is a note of computer network key points and useful tools and is organized according to the TCP/IP model.

Link Layer

ARP

MAC

PPP

CSMA/CD

Misc

CAN Bus

Internet Layer

IP (Internet Protocol)

IP address is a 32 bit number represented by a grouping of 4 octets.

192.168.0.1
In hex: c0 a8 00 01

CIDR

Classless Inter-Domain Routing.
Notation for talking about ranges of IP address.
Rare to see 192.168.0.0 - 192.168.0.255.
Instead you would see 192.168.0.0/24.
Equevalant to matching a netmask of 255.255.255.0.
value after the / is called the prefix length
0.0.0.0/8 = Class A
0.0.0.0/16 = Class B
0.0.0.0/24 = Class C

ICMP

RPC

A Request for Comments (RFC) is a formal document drafted by the Internet Engineering Task Force (IETF) that describes the specifications for a particular technology. When an RFC is ratified, it becomes a formal standards document.

RFCs were first used during the creation of the ARPANET (predecessor of Internet) protocols that came to establish what became today’s Internet. They continue to be issued on an ongoing basis as the technology underlying the Internet evolves.

Transport Layer

TCP

UDP

Application Layer

DNS

DNS resolves the network address to the IP address.

For linux, the local DNS server is in /etc/resolv.conf

DNS is a distributed and decentralized hierarchical database (organized by ICANN)

root server -> 13 labeled A-M
- some of the root servers have mirrors all the over world
Top Level Domain server
- com, org, edu
Authoritative DNS server
- amazon.com, utexas.edu

nslookup xxx.com will show up the IP address of the network address.

whois provides more info about the IP from the whois database

dig similar to nslookup

nmap is a network exploration tool and security / port scanner

-A aggressive, detect vulnerable,
-O OS detection

Zmap is a network tool for scanning the entire Internet (or large samples).

Computer Network Key notes.