Definition: layer 4-7

The two layers in a network packet that identify its content (for details about layers, see TCP/IP and OSI model). The bottom layers 1, 2 and 3 are the protocols that move a network packet from source to destination. Layers 4 and 7 identify the application that created the packets as well as the specifics of the request. For example, inspecting layer 4 can identify HTTP traffic (Web traffic), but inspecting layer 7 can determine what the HTTP request is for (see Web switch). See layer 4 switch and well-known port.

 TCP/IP SWITCHING/ROUTING DECISIONS

  Layer and      Forwarding
  Protocol       Decision
  Inspected      Based on

  2 - Ethernet   MAC address

  3 - IP         Network address
  3 - IP         Service quality

  4 - TCP/UDP    Traffic type
      socket     (HTTP, FTP, etc.)

  7 - HTTP       HTTP request type