What's changed: Initial version (topic 1.07, subtopics 1.07.1–1.07.4)
2.1Internet Protocol Fundamentals
Learn the foundations of TCP/IP: IP addresses, subnet masks and CIDR notation, private vs public IP addresses, the natures of TCP, UDP, and ICMP, well-known ports (22/25/53/80/123/443), and the differences between IPv4 and IPv6.
A networked server means IP addresses and protocol basics are unavoidable. This is a memorization-friendly area—polish CIDR arithmetic, port numbers, and the TCP vs UDP contrast into reliable points.
2.1.1IP addresses and subnetting
- An IPv4 address is 32 bits in dotted quads (192.168.1.10). The subnet mask (255.255.255.0) sets the boundary between network and host parts.
- CIDR writes the mask as "/bits" (192.168.1.0/24 = mask 255.255.255.0 = 8 host bits → up to 254 hosts; /26 gives 62). Subnetting borrows host bits to split networks.
- Private IP ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are for internal use; they reach the internet only translated to public addresses via NAT.
- IPv6 is 128 bits in colon-hex (2001:db8::1)—the structural fix for address exhaustion, designed without NAT, with auto-configured link-local addresses (fe80::/10).
2.1.2TCP, UDP, ICMP, and ports
- TCP is connection-oriented (3-way handshake, delivery and ordering guaranteed)—for web, SSH, anything needing integrity.
- UDP is connectionless (no acknowledgment, light, fast)—DNS queries, NTP, streaming. ICMP is for control and diagnostics (ping, unreachable notices) and has no ports.
- The six must-know well-known ports: 22/SSH, 25/SMTP, 53/DNS, 80/HTTP, 123/NTP, 443/HTTPS.
Instant-answer items: /24 = 254 hosts, the three private ranges (10/8, 172.16/12, 192.168/16), need delivery guarantees = TCP, speed first = UDP, ping = ICMP, 22=SSH, 53=DNS, 123=NTP, 443=HTTPS. Distractors love shuffling port numbers (25↔22, 53↔80).
CIDR math needs one fact: with n host bits you get 2^n addresses, 2^n−2 usable (minus the network and broadcast addresses). /24 → 254, /26 → 62, /30 → 2 (the router-link staple). Strengthen the TCP/UDP contrast with reasons: DNS uses UDP because a one-round-trip query cannot justify connection setup; the web uses TCP because HTML breaks if one byte is lost. For IPv6, exams probe the mindset shifts: hosts can hold global addresses without NAT; ICMPv6 is core protocol machinery (neighbor discovery—block it even less than in v4); and every interface auto-configures an fe80:: link-local address for on-link traffic.
| Aspect | TCP | UDP |
|---|---|---|
| Connection | Connection-oriented (handshake) | Connectionless |
| Reliability | Delivery and order guaranteed | No guarantees (light, fast) |
| Examples | HTTP/HTTPS, SSH, SMTP | DNS queries, NTP |
| ICMP (reference) | — | Diagnostics/control (ping), no ports |
Trap: "a /24 supports 256 hosts" is wrong—excluding the network and broadcast addresses leaves 254. "172.31.0.0 is public" is wrong too—the private range 172.16.0.0/12 spans 172.16.0.0–172.31.255.255 (a classic under-reading of /12). And "ping uses TCP" is wrong—ping is ICMP.
2.1.3Section summary
- CIDR = /n (usable hosts = 2^(32−n)−2); private ranges 10/8, 172.16/12, 192.168/16 (NAT to go outside)
- TCP = guarantees, UDP = light/fast, ICMP = diagnostics; the six ports 22 SSH, 25 SMTP, 53 DNS, 80 HTTP, 123 NTP, 443 HTTPS; IPv6 = 128-bit, NAT-free design, fe80:: link-local
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Quick check
(just a quick review)Q1. You build an internal network as 192.168.10.0/24. How many addresses can actually be assigned to hosts?
Q2. Which protocol and port are standard for DNS name-resolution queries?
Q3. Which is a correct private IP address range, not directly routable on the internet?