Network+ Lesson 4: IP Addressing

IPv4

- Internet Protocol version 4
- 32-bit addresses: about 4.3 billion unique addresses
- Address space is largely exhausted

IP Addresses V4

- Public Class A: 1.0.0.0 - 126.255.255.255
- Public Class B: 128.0.0.0 - 191.255.255.255
- Public Class C: 192.0.0.0 - 223.255.255.255
- Private (RFC1918, for LANs): 10.x.x.x, 172.16-31.x.x, 192.168.x.x
- APIPA: 169.254.0.0 - 169.254.255.255 (self-assigned when DHCP fails)

Other IP Addresses V4

- Multicast: 224.0.0.0 - 224.255.255.255 (one-to-many, group messaging)
- Layer 3 broadcast: 255.255.255.255 (all hosts, network layer)
- Layer 2 broadcast: FF:FF:FF:FF:FF:FF (all hosts, data link layer)
- Loopback: 127.0.0.0 - 127.255.255.255
- Loopback lets a host talk to itself; tests the network interface

Public IP

- Globally unique address used on the internet
- Lets a device be reached from anywhere

Private IP

- Used inside private networks; not routable on the internet
- Reaches the internet through a translating device (NAT)
- Ranges (RFC1918): 10.0.0.0 - 10.255.255.255
- 172.16.0.0 - 172.31.255.255
- 192.168.0.0 - 192.168.255.255

Automatic Private IP Addressing (APIPA)

- Self-assigned when a host can't reach a DHCP server
- Usable range: 169.254.0.1 - 169.254.255.254
- Local communication on the same subnet only
- No internet access
- Exam tip: a 169.254.x.x address means DHCP failed

IPv4 vs. IPv6

- IPv4: 32-bit addresses, about 4.3 billion addresses
- IPv6: 128-bit addresses, vastly larger address space
- IPv6 was created to fix IPv4 limits (address exhaustion)

IPv4 Subnetting

- Divides one network into smaller subnets
- Improves efficiency, security, and address management
- Can isolate traffic and improve performance

Classless (Variable-Length Subnet Mask) VLSM

- Part of CIDR (classless addressing)
- Subnets can be different sizes
- Each subnet uses a mask length that fits its host count
- Reduces wasted IP addresses

Classful

- Older method: address space split into fixed classes
- Classes A, B, C, D, E, each with a default subnet mask
- Rigid and wasteful; replaced by CIDR

Classless Inter-Domain Routing (CIDR) Notation

- Slash plus prefix length, e.g. 192.168.1.0/24
- /24 = first 24 bits are the network portion
- Allows VLSM; replaced classful design

IPv6

- 128-bit addresses: 3.4 x 10^38 addresses (fixes exhaustion)
- IPSec built in as a standard
- No broadcast: uses anycast and multicast instead
- Link-local addresses and autoconfiguration (can use the MAC address)
- Example: 2001:0db8:3c4d:0012:0000:0000:1234:56ab
- First 64 bits = prefix (48 routing + 16 subnet ID); last 64 = interface ID (host)

IPv6 Shortened Expression

- Original: 2001:0db8:3c4d:0012:0000:0000:1234:56ab
- Drop leading zeros: 2001:db8:3c4d:12:0000:0000:1234:56ab
- Write 0000 as 0: 2001:db8:3c4d:12:0:0:1234:56ab
- Replace consecutive all-zero fields with "::": 2001:db8:3c4d:12::1234:56ab
- "::" can appear only ONCE in an address

Other IPv6 Address Types

- Multicast: FF00::/8 (one-to-many, group messaging)
- Loopback: ::1 (host talks to itself; tests interface)
- Anycast: one-to-nearest; replaces IPv4 broadcast
- Unspecified: :: (default route; "any" address in filters)