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Networking Fundamentals · Foundational

Application Layer (L7)

OSI Layer 7 (and top layer of TCP/IP), which provides network services directly to user applications.

Definition

The Application layer contains the protocols that applications use to communicate, such as HTTP, DNS, SMTP, FTP, SSH, DHCP and SNMP. It is not the application itself but the interface the application uses to access the network. Next-generation firewalls and proxies that inspect these protocols are said to work at Layer 7.

Example

A browser uses HTTP, an Application-layer protocol, to request a web page.

Exam tip

The user program such as a browser is not "in" Layer 7; the protocols it uses are.

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