The TCP header contains various control information, various flags (what part of the session is this, what's the sequence number, source and destination TCP ports.
The IP header contains various control information, like source and destination IP and the encapsulated protocol (TCP, in this example). The ethernet header contains various control information, including the source and destination MAC addresses on the LAN. It may also (and usually does) have a "default gateway" (that is, an IP address through which it sends all packets going to somewhere other than a local subnet).Ībstractly, a packet destined for a web port looks something like: On the IP level, each machine has (at least) one IP, in (at least) one subnet. IP addressing is at some level symbolic, usually relying on lower-level network protocols (with less hierarchic structure) to actually complete the transmission.
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