Introduction to the Network Layer- Forwarding, Routing & Services
The Network Layer is like the postal service of the Internet its mission is to deliver data packets from one device to another, even if they’re separated by continents and multiple networks. At its core, this layer is responsible for host-to-host communication.
What Does the Network Layer Do?
The network layer ensures data moves correctly between machines by offering:
- Logical communication between hosts
- Routing and forwarding of data
- Addressing (IP addresses)
- Packet delivery across networks
The Internet Protocol (IP) is the backbone protocol used here especially IPv4 and IPv6.
Forwarding vs Routing
These two are often confused but serve very different purposes:
| Term | Meaning |
|---|---|
| Forwarding | Moving a packet to the correct output link at a router |
| Routing | Deciding which path a packet should take from source to destination |
Forwarding is a local operation(router-level) while Routing is a global decision-making process (network-wide)
Data Plane vs Control Plane - Inside the Router
Routers aren’t just dumb traffic directors. They contain two powerful internal planes:
- Data Plane - Handles the actual movement of packets. It uses the forwarding table to pick the next hop. It Operates at high speed and is usually in hardware.
- Control Plane - Decides where packets should go. It runs routing algorithms like OSPF (for internal networks) or BGP (between ISPs). It is executed in software.
Network Layer Service Model
In the Internet, the network layer operates on a best-effort delivery model. That means it tries to deliver your packets… but doesn’t make guarantees.
| Feature | Guaranteed by IP? | Explanation |
|---|---|---|
| Delivery Guarantee | ❌ | No guarantee the packet will arrive |
| Ordering | ❌ | Packets can arrive out of order |
| Timeliness | ❌ | No delay or latency guarantees |
| Duplicate Handling | ❌ | May deliver duplicate packets |
Higher-layer protocols (like TCP) build reliability on top of this.