IPv4
the Internet Protocol, version 4IPv4 is the addressing and delivery system of the internet. It gives every host a 32-bit address, wraps data in packets stamped with source and destination, and lets routers carry each one hop by hop — best-effort, across any number of networks.
IPv4 gives every host an address and carries packets to it hop by hop, best-effort.
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A datagram finds its way across a real LAN: forwarding decision, NAT/PAT at the gateway, TTL falling hop by hop.
How it works
Every router reads the destination address, forwards the packet one hop closer, and drops the TTL by one — so a packet that can’t find its way eventually dies instead of looping forever.
What IPv4 does, step by step
It stamps the data with a 32-bit source and destination address so any router can place it.
Each router matches the destination against its table and forwards the packet one step closer — independently, per packet.
Each hop drops the Time-To-Live by one; at zero the packet is discarded, killing routing loops.
If a link’s MTU is too small, the packet is split into fragments and reassembled at the destination.
In cybersecurity
IPv4 carries no identity and no encryption, so the source address can’t be trusted and the payload rides in the clear.
A forged source address hides the sender and powers reflection attacks; ingress filtering fights it.
Encrypt at the network layer with IPsec, or above it with TLS.
Overlapping or tiny fragments can evade filters and crash weak reassemblers.
Watching TTLs (as traceroute does) maps the path and fingerprints hosts.
Only ~4.3 billion addresses forced NAT everywhere — and pushed the move to IPv6.
Floods of spoofed packets saturate links regardless of what rides above.