6. Network Lower-Level Protocols

Network I/O is processed by many different layers and protocols, including the application, the protocol libraries, the TCP/IP stack, and the network interface driver. DTrace allows you to examine the internals of each layer, tracking a packet step-by-step as it is processed from the application to the network interface. Using DTrace, you can answer questions about system network load such as the following.

• What clients are requesting network I/O?

• To which TCP or UDP ports?

• Which processes are generating network I/O? Why?

• Are packets being dropped in the TCP/IP stack? Why?

As an example, connections is a DTrace-based tool you can use to trace inbound network connections:

Network-sniffing tools, such as ...

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