Learning path
Ports, subnetting, DNS and mail records, certificates and the logs that show what went wrong, with practice questions and the tools a network admin reaches for every day.
This path covers what a network administrator is asked about in the first months of the job: which ports a service uses, how addresses are split into subnets, whether a domain’s DNS and mail records are right, when a certificate runs out, and where the evidence is when something breaks.
The tool steps use the checks on this site, so you can try them against networks and domains you look after. Tick each one off when you have worked through it.
Every firewall rule, packet capture and "is it open?" question starts here.
Addressing is the job. Learn the block-size method once and subnet questions get quick.
Keep going until you can do five without the calculator.
A wrong mask on one host is a classic cause of "some things work, some do not".
Compare the address your PC has with the one the internet sees. That difference is NAT.
Check MX, SPF, DKIM and DMARC for a domain you look after, and read what each verdict means.
Expiry, issuer, names and chain: what to look at when a browser says a site is not secure.
Run weekly from cron, it warns you before a certificate lapses.
Before you troubleshoot your own network, check whether the cloud service is having a bad day.
Logs are where network problems leave their evidence.
Drive maps, printers and firewall rules for a whole domain are set here.
Printing is a network service too, and one of the most common tickets.
The same ideas in Azure: virtual networks, subnets, peering and network security groups.
