Internet addressing modes

Every device on the Internet needs an address so data can be delivered to it. Addressing works at four levels: physical (MAC), logical (IP), port, and domain name.

1. Physical (MAC) address

• 48-bit hardware address burned into the network card, written in hex (e.g. 00:1A:2B:3C:4D:5E).
• Works at the Data Link layer and identifies a device inside a local network.

2. Logical (IP) address

Works at the Network layer and identifies a host across networks.

IPv4: 32 bits, written in dotted decimal (e.g. 192.168.1.10), about 4.3 billion addresses.

Class	First octet range	Use
A	1–126	Very large networks (8-bit network, 24-bit host)
B	128–191	Medium networks (16/16)
C	192–223	Small networks (24/8)
D	224–239	Multicast
E	240–255	Reserved / experimental

IPv6: 128 bits, written in hex groups (e.g. 2001:0db8::1), a vastly larger address space.

Address types by delivery:

• Unicast: one sender to one receiver.
• Broadcast: one to all hosts in a network.
• Multicast: one to a selected group.
• Anycast (IPv6): one to the nearest of a group.

Private vs public: private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are used inside LANs; public addresses are globally routable. NAT translates between them.

3. Port address

• 16-bit number (0–65535) at the Transport layer that identifies the application/process on a host.
• Examples: HTTP 80, HTTPS 443, FTP 21, SMTP 25, DNS 53.
• Socket address = IP address + port, e.g. 192.168.1.10:80.

4. Domain names (URL/DNS addressing)

• Humans use names like www.example.com; DNS translates them to IP addresses.
• A URL gives the full address of a resource: protocol://host:port/path?query#fragment.

Summary

Level	Address	Layer	Size
Physical	MAC	Data Link	48 bits
Logical	IPv4 / IPv6	Network	32 / 128 bits
Port	Port number	Transport	16 bits
Name	Domain / URL	Application	text