OSI Reference Model
Definition
Seven-layer ISO/IEC 7498-1 model describing how network functions are partitioned: Physical, Data Link, Network, Transport, Session, Presentation, Application. A teaching model, not a deployed stack.
- Standard
- ISO/IEC 7498-1
- Layer count
- Seven
- Layers
- Physical, Data Link, Network, Transport, Session, Presentation, Application
- Role
- Conceptual teaching model, not a deployed protocol stack
Common questions
If OSI is not actually deployed, why do investigators still learn it?+
It gives a shared vocabulary for locating where an attack or artifact occurred, for example distinguishing a data-link-layer ARP spoofing attack from an application-layer SQL injection, even though real networks run TCP/IP.
How does OSI's seven-layer structure relate to the four-layer TCP/IP model used in practice?+
TCP/IP collapses several OSI layers together: its Link layer covers OSI's Physical and Data Link, and its Application layer covers OSI's Session, Presentation, and Application, while Network and Transport map roughly one to one.
Related terms
- CIDR (Classless Inter-Domain Routing)
- A compact notation for IP address ranges that appends a prefix length to the address, such as 192.168.1.0/24. The prefix length states...
- MAC Address (OUI)
- 48-bit hardware address. First 24 bits are the Organisationally Unique Identifier assigned by IEEE to a vendor; the lower 24 are the...
- RFC 1918 Private Space
- Three IPv4 ranges reserved for private use: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. Not routable on the public internet; require NAT at the edge.
- SLAAC
- Stateless Address Autoconfiguration. IPv6 host generates its own address from the router-advertised /64 prefix plus a 64-bit interface identifier (EUI-64 or RFC...
- TCP/IP Stack
- Four-layer model that actually runs the internet: Link, Internet, Transport, Application. Defined by the IETF and mapped onto the OSI layers for...