Layer 1: Physical The Physical layer consists of the physical media and dumb devices that make up the infrastructure of our networks. This pertains to the cabling and connections such as Category 5e and RJ-45 connectors. Note that this layer also includes light and rays, which pertain to media such as fiber optics and microwave transmission equipment. Attack considerations are aligned with the physical security of site resources. Although not flashy, physical security still bears much fruit in penetration (pen) testing and real-world scenarios.
Layer 2: Data Link The Data Link layer works to
ensure that the data it transfers is free of errors. At this layer, data
is contained in frames. Functions such as media access control and link
establishment occur at this layer. This layer encompasses basic
protocols such as 802.3 for Ethernet and 802.11 for Wi-Fi.
Layer 3: Network The Network layer determines the
path of data packets based on different factors as defined by the
protocol used. At this layer we see IP addressing for routing of data
packets. This layer also includes routing protocols such as the Routing
Information Protocol (RIP) and the Interior Gateway Routing Protocol
(IGRP). This is the know-where-to-go layer.
Layer 4: Transport The Transport layer ensures the
transport or sending of data is successful. This function can include
error-checking operations as well as working to keep data messages in
sequence. At this layer we find the Transmission Control Protocol (TCP)
and the User Datagram Protocol (UDP).
Layer 5: Session The Session layer identifies
established system sessions between different network entities. When you
access a system remotely, for example, you are creating a session
between your computer and the remote system. The Session layer monitors
and controls such connections, allowing multiple, separate connections
to different resources. Common use includes NetBIOS and RPC.
Layer 6: Presentation The Presentation layer
provides a translation of data that is understandable by the next
receiving layer. Traffic flow is presented in a format that can be
consumed by the receiver and can optionally be encrypted with protocols
such as Secure Sockets Layer (SSL).
Layer 7: Application The Application layer functions
as a user platform in which the user and the software processes within
the system can operate and access network resources. Applications and
software suites that we use on a daily basis are under this layer.
Common examples include protocols we interact with on a daily basis,
such as FTP and HTTP.