The Four Layers

Each layer rests on the one before it, if the bottom one fails, then all the others will come crashing down. But most of the time, if you fix that problem, then it’ll all magically right itself.

Layer Number	Layer Name	Layer Protocols/Items Related	Troubleshooting Tools	What it Does	Common Errors Related to it
1	Physical	Cables	Fixing/Checking the cable, ifconfig or ip a (checking networking configuration)	Sends the traffic.	Broken equipment, shoddy equipment, incompatible equipment
2	Datalink	ND (Neighbor Discovery, for IPv6), ARP (Address Resolution Protocol, for IPv4), MAC addresses	arp, ND (varies between OS’s), tcpdump and Wireshark	Transforms stuff into signals that could be chucked to the other side.	Frame errors (think packet errors), drops (think packet drops), overruns, collisions (these errors reduce performance, but might not necessarily bring down a network)
3	Network	IP (IPv4, IPv6)	ping, traceroute	Figures out where stuff goes.	Misconfiguration, support (e.g. only supports IPv4, configured to only support IPv6, different subnets, etc)
4	Transport	TCP - IP, UDP, ICMP, Ports(everything that has IP must support ICMP, ping sends traffic w/ ICMP)	netstat, netcat, tcpdump and Wireshark	As the name implies, transporting traffic.	No open ports, packet drops, misconfiguration, man-in-the-middle, etc

#networking #networking/layer1 #networking/layer2 #networking/layer3 #networking/layer4 #networking/conceptual