What happens if a router receives a packet larger than the Next Hop's MTU (e.g., 1500 bytes vs 1400 bytes) and the 'Don't Fragment' (DF) flag is set?

1. A The router automatically fragments the oversized packet into two smaller segments and forwards them independently to the destination for reassembly by the client.
2. B The router drops the packet and transmits an ICMPv4/v6 'Packet Too Big' message back to the sender, which is then used by the host to perform 'Path MTU Discovery' (PMTUD).
3. C The router applies a high-speed, lossy compression algorithm to the packet contents to ensure that the physical payload size fits within the constraints of the next hop.
4. D The router ignores the flag and attempts to force the entire packet through the interface, which typically results in a hardware-level network crash or a cascading routing failure.