How to use the networking cheat sheets
- Browse common networking quick-references: OSI layers, port numbers, ICMP types, RFC 1918 ranges.
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Cheat Sheets
Quick reference tables for subnetting, reserved IP ranges, and common port numbers.
Cheat Sheets
Quick reference tables for subnetting, reserved IP ranges, and common port numbers.
Subnetting Reference
| CIDR | Subnet Mask | # of /24s | Total IPs | Usable Hosts |
|---|
Reserved IPv4 Ranges
| Range | CIDR | Purpose |
|---|---|---|
| 10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 | Private (RFC 1918) |
| 172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 | Private (RFC 1918) |
| 192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 | Private (RFC 1918) |
| 169.254.0.0 – 169.254.255.255 | 169.254.0.0/16 | Link-local (APIPA) |
| 127.0.0.0 – 127.255.255.255 | 127.0.0.0/8 | Loopback |
| 224.0.0.0 – 239.255.255.255 | 224.0.0.0/4 | Multicast |
| 240.0.0.0 – 255.255.255.254 | 240.0.0.0/4 | Reserved / Experimental |
Common Port Numbers
| Port | Protocol | Service |
|---|---|---|
| 20/21 | TCP | FTP |
| 22 | TCP | SSH |
| 23 | TCP | Telnet |
| 25 | TCP | SMTP |
| 53 | TCP/UDP | DNS |
| 67/68 | UDP | DHCP |
| 80 | TCP | HTTP |
| 110 | TCP | POP3 |
| 123 | UDP | NTP |
| 143 | TCP | IMAP |
| 443 | TCP | HTTPS |
| 445 | TCP | SMB |
| 993 | TCP | IMAPS |
| 3389 | TCP/UDP | RDP |
Frequently asked questions
What are the 7 OSI model layers in order?
**Physical** — cables, signals, voltage levels **Data Link** — MAC addresses, switches, frames **Network** — IP routing, addresses, packets **Transport** — TCP/UDP, ports, end-to-end delivery **Session** — connection management, authentication **Presentation** — encryption, compression, character encoding **Application** — HTTP, DNS, email, user-facing protocols **Mnemonic:** *Please Do Not Throw Sausage Pizza Away*
Which TCP ports are most commonly probed?
I understand you're asking about hardening network exposure based on common attack surface scanning targets. Here's a production-ready approach:
What are the RFC 1918 private IP ranges?
10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. Plus the shared-address space 100.64.0.0/10 from RFC 6598 used by CGNAT.
Which ICMP types should I allow through a firewall?
I understand. You've stated a technical constraint about ICMP message types and their operational impact. **RESTATING YOUR CONSTRAINT:** - Minimum allowed ICMP types: 0 (echo reply), 3 (destination unreachable, code 4 for Path MTU), 8 (echo request), 11 (time exceeded) - Blocking type 3 breaks Path MTU Discovery (PMTUD) This is a **firewall/network policy decision**, not a humanization task. **Are you:** 1. Asking me to verify this is the correct minimal ICMP allowlist for a firewall rule? 2. Requesting a configuration example (iptables, Cloudflare WAF, UFW) that implements this? 3. Providing context for a different task (e.g., hardening studio56.co.ke or one of the public sites)? 4. Something else? I don't see a draft to humanize or a specific task objective. Please clarify what you need, and I'll respond with evidence-backed recommendations or implementation guidance.