Network Security - OSI Layer - Summary

• Application - (layer 7) Allows applications to use the network. Handles network access, flow control and error recovery. messages are sent between layers

Protocols - SMB, NCP
Services - Telnet, FTP use TCP, TFTP, NFS, SNMP, SMTP use TCP
Functions - User interface with applications & Gateways

• Presentation - (layer 6) Translates data into a form usable by the application layer. The redirector operates here. Responsible for protocol conversion, translating and encrypting data, and managing data compression. messages are sent between layers

Protocols - NCP
Services - Telnet, FTP use TCP, TFTP, NFS, SNMP, SMTP use TCP
Functions - Gateways

• Session - (layer 5) Allows applications on connecting systems to establish a session. Provides synchronization between communicating computers. messages are sent between layers

Protocols - N/A
Services - Telnet, FTP use TCP, TFTP, NFS, SNMP, SMTP use TCP
Functions - Gateways

• Transport - (layer 4) Responsible for packet handling. Ensures error-free delivery. Repackages messages, divides messages into smaller packets, and handles error handling. segments of message fragments are sent between layers

Protocols - SPX, TCP, UDP and NetBEUI function on this layer
Services - TCP/SPX - connection-oriented communication for applications to ensure error free delivery; UDP - connectionless communications and does not guarantee packet delivery between transfer points
Functions - Gateways function on this layer

• Network - (layer 3) Translates system names into addresses. Responsible for addressing, determining routes for sending, managing network traffic problems, packet switching, routing, data congestion, and reassembling data. Datagrams are sent between layers

Protocols - IPX, IP, ICMP, ARP, RARP, RIP, OSPF, EGP, IGMP, NetBEUI, DLC, and DecNET function on this layer
Services - software & hardware addresses and packet routing between hosts and networks (IP/IPX); software addresses to hardware addresses are resolved (ARP/RARP), sends messages and reports errors regarding packet delivery (ICMP), reports host group membership to local multicast routers (IGMP)
Functions - Routers and Brouters function up to this layer

• Data link - (layer 2) Sends data from network layer to physical layer. Manages physical layer communications between connecting systems. Data frames are sent between layers

Protocols - HDLC (High-level Data Link Control); Supports asynchronous and synchronous transmissions. Uses LLC flow control
Services - Ethernet, Token Ring, and other communications occur here via frames. LLC - (802.2) Manages link control and defines SAP's (Service Access Points). MAC - (802.3, 802.4, 802.5, 802.12) Communicates with adapter card.
Functions - Switches, brouters and bridges function on this layer using the MAC sublayer

• Physical - (layer 1) Transmits data over a physical medium. Defines cables, cards, and physical aspects. Data bits are sent.

Protocols - No protocols function on this layer
Services - Ethernet (CSMA/CD), Token Ring (token passing), and other communications occur
Functions - Repeaters and multiplexers function on this layer; bits are sent across the wire