“Seems like an awful lot just to get a packet from one side of the
room to the other.”
An anonymous networking student
Chapter 1 discussed several
of the issues associated with forwarding traffic across a network.
Communication flows from one host to another (usually a server of some kind)
and then back again. Switch source address and router routing tables are
critical to this process. But, no matter what the purpose of the
transmission, several operations must take place before packets can enter
the network, beginning with the host routing table. Integrated ideas include
masking, address resolution, and default gateways.
The Decision Process
From the moment a source host generates a chunk of data for
transmission, work begins that will eventually result in an Ethernet frame
being transmitted. From the application layer on down, the data is
encapsulated in a series of headers until it reaches the bottom of the
protocol stack. For example, accessing a web page uses the hypertext
transfer protocol (HTTP) to move information between the web server and
the host. HTTP uses the transmission control protocol (TCP) at Layer 4
followed by IP and then Ethernet or 802.11. If we assume Ethernet, the
encapsulated data would look like that seen in Figure 2-1.
Figure 2-1. Encapsulation
As the encapsulation nears completion, the source and destination MAC addresses have to be filled ...
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