RE: ARP Spoof Question

  Layers are an agreed-upon decomposition of the general problem of getting devices to communicate over a network, which allow different pieces of the solution to be implemented by different teams/vendors and yet interoperate. Just about *any* network text devotes one of the early chapters to a layer model, usually the ISO 7-layer model although some treat the ARPA 4-layer model as a subset of ISO, and some as an alternative.

  The ISO model, briefly:

1. Physical Layer What is the arrangement of conductors in the cable? What do the connectors look like? What sorts of voltage and current is carried (if this layer is electrical, which might not be the case)?
2. Data Link Layer How are bits arranged on the physical media to form larger entities (frames)? How are sources and destinations identified (MAC addressing)?
3. Network Layer How are networks and hosts identified, so that packets can be routed across multiple networks?
4. Transport Layer How are streams of traffic broken into sequences of packets, and reassembled into streams at the other end?
5. Session Layer This layer should allow multiple streams to be associated with a shared context. It hasn't found wide use yet.
6. Presentation Layer Translations between host and network representations fit nicely at this level. It would also be a good place to put encryption of content, although most current approaches opt instead to provide an encrypted Transport layer.
7. Application Layer The application layer provides the interface between user and server processes and the network communications system.

David Gillett

> -----Original Message-----