Overview
Fragmentation occurs at the Network Layer (Layer 3). When a router receives a packet larger than the outgoing interface's MTU, it splits the packet into fragments. Each fragment has its own IP header with the 'Fragment Offset' field set to help the destination reassemble them.
Downsides
- CPU Overhead: Routers must spend resources splitting packets.
- Reliability: If a single fragment is lost, the entire original packet is considered lost and must be retransmitted.
- Security: Some firewalls struggle to inspect fragmented traffic.