Ports and Protocols
Common Ports Unwrapped! Web, Mail and Names
A new firewall went in on Friday. Monday morning the website works, incoming email works, and nobody can send a single message. If you know your doors, this ticket takes one look. This is the first Common Ports lesson: the numbers the exam asks about more than almost anything else, taught as the numbered garage doors of Byte City, and paid off on one real ticket.
You'll learn
- Why every computer has 65,536 doors, and why the first 1,024 (the well-known ports) are the ones worth memorising
- The two vehicles: the cube truck (TCP) and the bullhorn (UDP), and which doors expect which
- 80 and 443: the storefront plain and the storefront with the lock — HTTP and HTTPS
- The mail doors: 25 (SMTP between servers), 587 (SMTP submission from your own mail app), 143/993 (IMAP, read and keep), 110/995 (POP3, read and take)
- 53: the Yellow Pages, DNS — the bullhorn for lookups, the truck for large answers and zone transfers
- A port identifies the service, not the machine; address + port = a socket; your own side uses an ephemeral port
- The real thing: netstat on the server, Test-NetConnection door by door from a laptop, and the firewall rule that was missing
- Exam corner: users can browse and receive mail but cannot send — which port is blocked?
Chapters
- 0:00The Friday firewall
- 0:32The house and its doors
- 0:4765,536 doors, three ranges
- 1:21The truck and the bullhorn
- 1:44The storefront: 80 and 443
- 2:37The mail doors: 25, 587, 143/993, 110/995
- 3:37Back to the Friday firewall
- 3:54Door 53: DNS, both vehicles
- 4:48The real names: the list
- 5:17Sockets and the return door
- 5:47The real thing: netstat, Test-NetConnection, the firewall rule
- 6:43Exam corner
- 6:58Recap and next time
Exam objectives: CompTIA Network+ N10-009: 1.4 (common ports and protocols: HTTP 80, HTTPS 443, SMTP 25, SMTPS 587, DNS 53), 1.1 (transport layer, TCP and UDP), 5.5 (netstat, Test-NetConnection). IMAP 143/993 and POP3 110/995 are taught as well; they are beyond the current N10-009 port list but still common in practice.
Byte City is not affiliated with or endorsed by CompTIA.