IPv4

Internet Protocol version 4 assigns a 32‑bit address to every device on the network. Addresses are written in dotted‑decimal form such as 192.0.2.5.

Header Fields

• Version & IHL – specify IPv4 and header length
• Total Length – the entire packet size
• Identification, Flags, Offset – used when a router fragments packets
• TTL – decremented at each hop to avoid endless loops
• Protocol – indicates the payload type (TCP, UDP, etc.)

Fragmentation

Routers split packets that exceed a link's MTU. Fragments share the same Identification value and carry offsets so the destination can reassemble them.

Address Classes & CIDR

Early networks divided addresses into A, B and C classes, but today CIDR allows allocating arbitrary prefix lengths like /24 or /30 for efficiency.