STEM · Full roadmap · ~110 min read · 34 steps
🌐IT Support Level 3: Network and Server Support
Diagnose networks, subnet by hand, and support servers like an L3 engineer
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Unit 1
Start here
Course overview
What changes at level 3
L3 is the subject-matter expert who finds root cause
The OSI model as a map
Seven layers that split a network problem into pieces
Layers you will actually touch
Physical, Data Link, Network, Transport, and Application do the real work
TCP/IP model and encapsulation
Data gets wrapped in headers as it goes down the stack
Unit 2
IPv4 addresses and what they mean
32 bits split into a network part and a host part
CIDR notation and the slash
The /number counts how many bits are the network part
Subnetting: the host count
Hosts equal 2 to the power of host bits, minus 2
Subnetting: finding the ranges
The block size tells you where each subnet starts and ends
Private ranges and NAT
Private IPs stay inside, NAT translates them to one public IP
Unit 3
A short word on IPv6
128-bit addresses, written in hex, with no need for NAT
DNS, the name to number system
DNS turns names people remember into IP addresses machines route
DHCP, automatic addressing
DHCP hands out IP, mask, gateway, and DNS automatically
Common ports and protocols
Each service listens on a known port number
Switching: MAC tables and VLANs
Switches forward by MAC address and segment with VLANs
Unit 4
Trunking and spanning tree
Trunks carry many VLANs; STP stops loops from melting the network
Routing: moving between networks
Routers use a routing table to pick the next hop
Dynamic routing and where OSPF and BGP live
Routing protocols share routes automatically across the network
Network hardware in the rack
Switch, router, firewall, access point, load balancer each have one job
Wireless: bands, channels, and interference
Wi-Fi shares the air, so channels and bands decide performance
Unit 5
Enterprise wireless and 802.1X
Business Wi-Fi authenticates each user, not one shared password
Troubleshooting methodology
Work bottom-up the layers and change one thing at a time
The diagnostic toolkit
ping, traceroute, dig, netstat, and a packet capture each answer one question
Firewalls and basic network security
ACLs filter by port and address; VPNs extend the network securely
Server roles and operating systems
A server is a role plus an OS, usually Windows Server or Linux
Unit 6
RAID levels explained
RAID combines disks for redundancy, speed, or both
Virtualization and hypervisors
One physical server runs many virtual machines via a hypervisor
Active Directory and FSMO roles
Domain controllers run AD, depend on DNS, and replicate; five FSMO roles coordinate
Group policy and managing the fleet
Group Policy pushes settings to many machines and users from one place
Monitoring and alerting
SNMP, syslog, and uptime checks tell you something broke before users do
Unit 7
Backup and disaster recovery
The 3-2-1 rule plus RTO and RPO define how you survive a failure
Where cloud fits and why your skills transfer
IaaS, PaaS, and SaaS move responsibility up the stack, but the fundamentals stay
Common mistakes and a practice routine
Avoid the classic L3 traps and build the reflexes that prevent them
Where to go next
Where to go next