NetOps Toolkit

Reference

OSI Model

Interactive 7-layer OSI model with protocols, PDUs, and devices

Not sure what layers mean? Think of it like sending a letter — you write it (Layer 7), seal it in an envelope (Layer 6–5), address it (Layer 3–4), hand it to the postal worker (Layer 2), and they carry it physically (Layer 1). Each layer adds a wrapper to the data.
Top-down: All People Seem To Need Data Processing  |  Bottom-up: Please Do Not Throw Sausage Pizza Away
  1. 7

    Application Data

    End-user services and application protocols. Where users interact with network services.

    HTTP, HTTPS, FTP, SSH, DNS, DHCP, SMTP, SNMP, Telnet, LDAP, RDP, SIP

  2. 6

    Presentation Data

    Data formatting, encryption, compression, and translation between application and network formats.

    SSL/TLS, JPEG, PNG, MPEG, ASCII, GIF, encryption/compression

  3. 5

    Session Data

    Session management — establishes, maintains, and terminates connections between applications.

    NetBIOS, RPC, PPTP, SCP, NFS, SQL sessions

  4. 4

    Transport Segment

    End-to-end delivery, segmentation, reassembly, flow control, error recovery. Ports live here.

    TCP (reliable, connection-oriented), UDP (fast, connectionless)

  5. 3

    Network Packet

    Logical addressing (IP) and routing. Devices: Router, Layer 3 Switch.

    IPv4, IPv6, ICMP, OSPF, BGP, EIGRP, ARP, IPSec

  6. 2

    Data Link Frame

    MAC addressing, switching, error detection (CRC), frame delivery. Devices: Switch, Bridge, WAP.

    Ethernet, 802.11 WiFi, STP, VLANs, PPP, LLDP, CDP, ARP

  7. 1

    Physical Bits

    Physical transmission — cables, connectors, signals, voltages, light pulses, radio waves.

    Copper (Cat5e/6/6a), Fiber (OM3/OM4/OS2), Coax, WiFi radio, Hubs, Repeaters