A2.3.1 Describe different types of IP addressing.
• The distinction between IPv4 and IPv6 addressing
• The differences between public IP addresses and private IP addresses, and between static IP addresses and dynamic IP addresses
• The role of network address translation (NAT) to minimize the use of IP addresses and to facilitate communication between private internal networks and the public internet
Big idea
An IP (Internet Protocol) address is a binary identifier assigned to devices participating in a network that utilizes the Internet Protocol for communication. It functions both as a unique identifier (host identification) and a locator (network routing), enabling data to be correctly routed between source and destination nodes in packet-switched architectures such as the Internet.
IP addressing is central to all forms of modern networking—from LANs (Local Area Networks) to the global Internet—and underpins essential protocols such as TCP, UDP, ICMP, and BGP.
IP addressing is the system that lets every device on an internetwork — from laptops to cloud servers — be uniquely identified so that packets can be routed end-to-end. An “address” is therefore a logical label, written in a standard format, that sits inside every IP header and tells routers two things: where the packet came from and where it must go. Understanding the different types of IP addresses is essential because each type solves a distinct scaling, routing, or security problem.
1. IPv4 versus IPv6
| Property | IPv4 | IPv6 |
|---|---|---|
| Address length | 32 bits (≈ 4.29 × 10⁹ addresses) | 128 bits (≈ 3.4 × 10³⁸ addresses) |
| Notation | Dotted-decimal, e.g. 192.0.2.14 | Colon-hexadecimal, e.g. 2001:0db8:85a3::8a2e:0370:7334 |
| Header size | 20 bytes (base) | 40 bytes (base) |
| Built-in features | Limited to optional fields (e.g., fragmentation) | Native IPsec, stateless address autoconfiguration (SLAAC), flow labels, no broadcast (uses multicast instead) |
| Deployment status | Mature, still dominant but address pool exhausted | Growing rapidly; required for emerging IoT and 5G scale |
Describe level insight: IPv6 does not replace IPv4 by redesigning the whole Internet; it extends the address space and streamlines routing while retaining the same best-effort packet-delivery model.
2. Public and Private IP addresses
Public IP addresses
Globally routable numbers assigned by Regional Internet Registries (RIRs). Because every public address must be unique across the entire Internet, their supply is limited (especially for IPv4).
Private IP addresses
Locally significant ranges reserved by RFC 1918 (IPv4) and Unique-Local Addresses, ULA, in IPv6 (fc00::/7). Routers on the public Internet drop these prefixes; they are meant to stay inside an organisation’s boundary.
| Reserved IPv4 range | Typical use |
|---|---|
10.0.0.0/8 | Large internal LANs, data centres |
172.16.0.0/12 | Mid-sized enterprise networks |
192.168.0.0/16 | Home routers and small offices |
Describe level insight: Private addressing decouples an enterprise’s internal topology from the global table, allowing unlimited reuse inside separate organisations.
3. Static and Dynamic IP addresses
| Aspect | Static addressing | Dynamic addressing |
|---|---|---|
| How assigned | Manually configured or permanently leased | Handed out automatically, usually by DHCP (IPv4) or SLAAC/DHCPv6 (IPv6) |
| Lifetime | Indefinite until administrator changes it | Lease time-bound; may change when the client reconnects |
| Typical workloads | Servers, network devices, anything that must be reachable via a predictable address (DNS records, VPN gateways) | Client PCs, phones, IoT sensors, guest WLAN users |
| Operational trade-offs | Predictability, but higher management overhead and risk of duplicate entries | Scales effortlessly, but endpoints may need Dynamic DNS or other discovery methods |
Describe level insight: Static vs dynamic is orthogonal to public vs private — for example, a web server can have a static public IPv4 address, whereas a laptop on hotel Wi-Fi often receives a dynamic private address.
4. Network Address Translation (NAT)
Core concept
NAT is a forwarding technique where a border device rewrites packet headers so that many private internal addresses appear to the Internet as one (or a few) public addresses.
Inside host 192.168.1.10:45218 ──▶ NAT router 203.0.113.5:60234 ──▶ Web server 198.51.100.7:443
Why NAT matters
- Address conservation — thousands of internal IPv4 hosts can share a single global address, delaying exhaustion.
- Policy boundary — the NAT box doubles as a stateful firewall, scrutinising outbound flows and allowing return traffic only for legitimate sessions.
- Topology hiding — internal address plans stay private, simplifying mergers and multi-tenant designs.
Main flavours
| Type | How it works | Common use |
|---|---|---|
| Static 1-to-1 NAT | Fixed mapping between one private and one public IP | Publishing a private server when only one public address is left |
| Dynamic NAT | Draws from a pool of public addresses as sessions open | Large enterprises with an allocated public block |
| Port Address Translation (PAT/NAT overload) | Maps many private hosts to one public address using unique TCP/UDP port pairs | Home routers, small offices |
Describe level insight: NAT is a workaround for IPv4 scarcity; IPv6, with its vast address pool, can eliminate the need for NAT, yet many networks still deploy “NAT66” for the perceived security and simplicity of a single egress point.
Putting it together
A modern campus might therefore run:
- IPv4 + NAT to serve legacy systems and provide Internet access via a single
/29public block. - Dual-stack IPv4/IPv6 on the backbone so internal devices can reach IPv6-only cloud services natively.
- Private dynamic pools for student laptops, private static addresses for lab printers, and public static addresses for research servers that require global visibility.
By combining these addressing techniques, network engineers juggle scalability, reachability, manageability and security — all atop the same physical cables.