OSI Model

No networking class is complete without dragging out the good old Open Systems Interconnection (OSI) reference model. The OSI model abstracts network communications into seven separate layers. Each layer (in theory) hides their inner workings from the others while performing some critical function. It is important to note that this is a “model” meaning many protocols/real world network implementations do not fit neatly into each layer. If you are interested in some of the history surrounding the OSI model, check out my other post on ARPANET.

The OSI Model

#Layer NameDevicesProtocols
1Physicalcables, hubsPhysical layer of most Layer 2 devices
2Data Linkswitches802.3 Ethernet, 802.11 WiFi
3Networkrouters, layer 3 switchesIPv4, IPv6, IPsec, ICMP, routing protocols (like BGP)
4TransportNATCP, UDP
5SessionNAOften combined with Application Layer in TCP/IP model. OSI refers to this layer as containing control and/or tunneling protocols (NetBIOS)
6PresentationNAOften combined with Application Layer in TCP/IP model. OSI refers to this layer as containing application encryption protocols (SSL/TLS, MIME)
7Applicationeverything elseDNS, FTP, FTPS, HTTP, HTTPS, IMAP4, POP3, LDAP, RDP, SSH, Telnet, SMTP, SNMP, SFTP, etc.

References

The Internet has plenty of resources on the OSI model from wikipedia to the TCP/IP Guide. For more on TCP/IP protocols, check out my post on TCP/IP.

ABOUT LAURA KAPLAN

Throughout my 10 year career I have worked as a web developer, systems administrator, software engineer, security analyst and now cybersecurity engineer. I currently develop software applications to automate security vulnerability and compliance scanning and reporting for a multinational financial institution.