Real problems P4 solves
Visibility that actually tells you something
Traditional monitoring gives you SNMP counters (updated every 30 seconds, way too slow) or NetFlow samples (statistically useful but incomplete). Neither tells you what happened to a specific transaction at a specific moment.
P4 changes this completely. Your switches and SmartNICs can add metadata to packets as they flow through timestamps, queue depths and congestion indicators. The application receiving the packet gets real data about what happened in the network. A database query that normally takes 5ms suddenly takes 50ms? You know exactly which device had congestion, when it happened, and how bad it was.
Real example: A retail company deployed P4 telemetry on both their switches and server SmartNICs before Black Friday. Their traditional monitoring showed everything looked normal. Average latency within bounds, no packet loss. But P4 telemetry revealed that 2% of shopping cart transactions were hitting 500ms delays. Turned out specific switch ports had misconfigured buffers that only showed up under bursty traffic. They found and fixed it before it became a revenue problem. Their old monitoring system would’ve completely missed this.
Security at every layer
Most networks handle DDoS protection with dedicated appliances. Expensive boxes positioned at chokepoints. P4 moves that protection everywhere, from the network fabric to the server edge.
Simple example: DNS amplification attacks. A P4 program on a SmartNIC tracks query-to-response ratios per source IP. See 1 query and 50 responses? That’s amplification. Drop the responses automatically before they even reach the server CPU. The SmartNIC maintains state, makes decisions, and acts. All at wire speed while forwarding legitimate traffic normally.
More advanced implementations get really interesting. One financial services company uses P4 on SmartNICs to enforce API call sequences at the server edge. You must call their authentication endpoint first, then data endpoints, then logout. Try to grab data without authenticating? The P4 program drops your packets immediately at the NIC, before consuming any server resources. It’s maintaining per-connection state machines, something very hard to achieve with traditional fixed-function switches and NICs.
