TCP/IP in Detail

This lesson covers the details of the Internet layer and related services: IP addressing (IPv4 and IPv6), subnetting, DNS, DHCP, NAT, port numbers, and the difference between TCP and UDP. These are essential for the OCR H446 specification.

---

IP Addresses

An IP address is a unique numerical identifier assigned to every device on a network that uses the Internet Protocol.

IPv4

IPv4 (Internet Protocol version 4) uses 32-bit addresses, written as four octets (groups of 8 bits) in dotted decimal notation.

Feature	Detail
Format	4 octets: xxx.xxx.xxx.xxx
Bits	32 bits total
Range	0.0.0.0 to 255.255.255.255
Total addresses	2^32 = approximately 4.3 billion
Example	192.168.1.100

IPv6

IPv6 (Internet Protocol version 6) was developed to address the exhaustion of IPv4 addresses.

Feature	Detail
Format	8 groups of 4 hexadecimal digits, separated by colons
Bits	128 bits total
Total addresses	2^128 = approximately 3.4 x 10^38
Example	2001:0db8:85a3:0000:0000:8a2e:0370:7334
Shortened	Leading zeros can be omitted; consecutive groups of zeros can be replaced with ::

IPv4 vs IPv6

Feature	IPv4	IPv6
Address length	32 bits	128 bits
Address format	Dotted decimal	Hexadecimal with colons
Total addresses	~4.3 billion	~3.4 x 10^38
Address exhaustion	Running out	Effectively unlimited
Security	Optional (IPSec)	Built-in (IPSec mandatory)
Configuration	Manual or DHCP	Auto-configuration supported
Header	Variable length, more complex	Fixed length, simpler

---

Subnetting

Subnetting divides a large network into smaller, more manageable sub-networks (subnets).

How Subnetting Works

An IP address is split into two parts:

• Network part: Identifies the network
• Host part: Identifies the specific device on that network

A subnet mask determines which bits belong to the network part and which to the host part.

Subnet Mask Example

IP Address	192.168.1.100
Subnet Mask	255.255.255.0
Network Part	192.168.1 (first 24 bits)
Host Part	.100 (last 8 bits)
CIDR Notation	192.168.1.100/24

Benefits of Subnetting

Benefit	Explanation
Reduced congestion	Smaller broadcast domains reduce unnecessary traffic
Improved security	Different subnets can have different access policies
Better organisation	Departments or floors can have their own subnet
Efficient IP usage	Allocate only the number of addresses needed per subnet

---

DNS (Domain Name System)

DNS translates human-readable domain names (e.g., www.example.com) into IP addresses (e.g., 93.184.216.34).

Why DNS is Needed

Humans find domain names easy to remember, but computers need IP addresses to route data. DNS bridges this gap.

How DNS Works

1. User types "www.example.com" into their browser.
2. The browser checks its local cache for a stored IP address.
3. If not cached, the request goes to the ISP's recursive DNS resolver.
4. The resolver queries the root DNS server, which directs it to the .com TLD server.
5. The TLD server directs the resolver to the authoritative DNS server for example.com.
6. The authoritative server returns the IP address (e.g., 93.184.216.34).
7. The resolver caches the result and returns it to the browser.
8. The browser connects to the web server at that IP address.

DNS Record Types

Record Type	Purpose
A	Maps a domain to an IPv4 address
AAAA	Maps a domain to an IPv6 address
CNAME	Alias — maps one domain to another
MX	Mail exchange — specifies mail servers for the domain
NS	Nameserver — specifies authoritative DNS servers

---