Protocols Per Layer

3 minute read


Protocols are methods that computers use to talk to each other. Throughout your IT career you will learn different ones and how they relate to the OSI model.

  • You can view common ports on the home page or here
  • I recommend you download all the cheat sheets from the site here
Port Number Protocol Name Description
21 FTP File Transfer Protocol
22 SSH/ SCP Used for secure connections
25 SMTP Used to send emails
53 DNS Used to translate IP to domain names
80 HTTP Protocol used to browse the web. More info here
110 POP3 Email Protocol
143 IMAP4 Email Protocol
161-162 SNMP Network device communication protocol
443 HTTPS Secure HTTP
989-990 FTP over SSL Secure FTP
993 IMAP4 over SSL Secure IMAP
995 POP3 over SSL Secure POP

Layer 1 Protocols: The Physical Layer

  • ADSL => Asymmetric digital subscriber line
  • ISDN => Integrated Services Digital Network
  • PDH => Plesiochronous Digital Hierarchy
  • T-carrier => (T1, T3, etc.)
  • E-carrier => (E1, E3, etc.)
  • RS-232 => a serial line interface originally developed to connect modems and computer terminals
  • SDH => Synchronous Digital Hierarchy
  • SONET Synchronous Optical NETworking
  • Modem standards/ITU V-Series Protocols used to communicate between analog modems over voice telephone lines.
  • Various Ethernet physical layers
  • ARCnet
  • CDP Cisco Discovery Protocol
  • DCAP Data Link Switching Client Access Protocol
  • Dynamic Trunking Protocol
  • Econet
  • Ethernet
  • FDDI Fiber Distributed Data Interface
  • Frame Relay
  • HDLC High Level Data Link Control
  • IEEE 802.11
  • IEEE 802.16
  • LocalTalk
  • L2F Layer 2 Forwarding Protocol
  • L2TP Layer 2 Tunneling Protocol
  • LAPD Link Access Procedures on the D channel
  • LLDP Link Layer Discovery Protocol
  • LLDP-MED Link Layer Discovery Protocol => Media Endpoint Discovery
  • PPP Point-to-Point Protocol
  • PPTP Point-to-Point Tunneling Protocol
  • Q.710 Simplified Message Transfer Part
  • NDP Neighbor Discovery Protocol
  • SLIP Serial Line Internet Protocol (obsolete)
  • StarLan
  • STP Spanning Tree Protocol
  • Token ring
  • VTP VLAN Trunking Protocol

Layer 2+3 Protocols:

  • ATM Asynchronous Transfer Mode
  • Frame relay, a simplified version of X.25
  • MPLS Multi-protocol label switching
  • X.25
  • ARP Address Resolution Protocol
  • RARP Reverse Address Resolution Protocol

Layer 1+2+3 Protocols:

  • MTP Message Transfer Part
  • NSP Network Service Part

Layer 3 Protocols: Network Layer

  • CLNP Connectionless Networking Protocol
  • EGP Exterior Gateway Protocol
  • EIGRP Enhanced Interior Gateway Routing Protocol
  • ICMP Internet Control Message Protocol
  • IGMP Internet Group Management Protocol
  • IGRP Interior Gateway Routing Protocol
  • IPv4 Internet Protocol version 4
  • IPv6 Internet Protocol version 6
  • IPSec Internet Protocol Security
  • IPX Internetwork Packet Exchange
  • MPLS Multiprotocol Label Switching
  • SCCP Signalling Connection Control Part

Layer 3 Protocols: Network Layer management

  • IS-IS Intermediate system to intermediate system
  • OSPF Open Shortest Path First
  • BGP Border Gateway Protocol
  • RIP Routing Information Protocol

Layer 3.5 protocols

  • HIP Host Identity Protocol

Layer 3+4 protocols

  • Xerox Network Services

Layer 4 Protocols: Transport Layer

  • AHAH Authentication Header over IP or IPSec
  • ESPESP Encapsulated Security Payload over IP or IPSec
  • GRE Generic Routing Encapsulation for tunneling
  • IL Originally developed as transport layer for 9P
  • SCTP Stream Control Transmission Protocol
  • Sinec H1 for telecontrol
  • SPX Sequenced Packet Exchange
  • TCP Transmission Control Protocol
  • UDP User Datagram Protocol

Layer 5 Protocols: Session Layer

  • 9P Distributed file system protocol developed originally as part of Plan 9
  • NCP NetWare Core Protocol
  • NFS Network File System
  • SMB Server Message

Layer 7 Protocols: Application Layer

  • AFP, Apple Filing Protocol
  • BACnet, Building Automation and Control Network protocol
  • BitTorrent, A peer-to-peer file sharing protocol
  • BOOTP, Bootstrap Protocol
  • Diameter, an authentication, authorization and accounting protocol
  • DICT, Dictionary protocol
  • DNS, Domain Name System
  • DHCP, Dynamic Host Configuration Protocol
  • ED2K, A peer-to-peer file sharing protocol
  • FTP, File Transfer Protocol
  • Finger, which gives user profile information
  • Gnutella, a peer-to-peer file-swapping protocol
  • Gopher, a hierarchical hyperlinkable protocol
  • HTTP, HyperText Transfer Protocol
  • IMAP, Internet Message Access Protocol
  • IRC, Internet Relay Chat protocol
  • ISUP, ISDN User Part
  • Jabber, an instant-messaging protocol
  • LDAP Lightweight Directory Access Protocol
  • MIME, Multipurpose Internet Mail Extensions
  • MSNP, Microsoft Notification Protocol (used by Windows Live Messenger)
  • MAP, Mobile Application Part
  • NetBIOS, File Sharing and Name Resolution protocol => the basis of file sharing with Windows.
  • NNTP, News Network Transfer Protocol
  • NTP, Network Time Protocol
  • NTCIP, National Transportation Communications for Intelligent Transportation System Protocol
  • POP3 Post Office Protocol Version 3
  • RADIUS, an authentication, authorization and accounting protocol
  • Rlogin, a UNIX remote login protocol
  • rsync, a file transfer protocol for backups, copying and mirroring
  • RTP, Real-time Transport Protocol
  • RTSP, Real-time Transport Streaming Protocol
  • SSH, Secure Shell
  • SISNAPI, Siebel Internet Session Network API
  • SIP, Session Initiation Protocol, a signaling protocol
  • SMTP, Simple Mail Transfer Protocol
  • SNMP, Simple Network Management Protocol
  • SOAP, Simple Object Access Protocol
  • TUP, Telephone User Part
  • Telnet, a remote terminal access protocol
  • TCAP, Transaction Capabilities Application Part
  • TFTP, Trivial File Transfer Protocol, a simple file transfer protocol
  • WebDAV, Web Dist Authoring and Versioning


“List of Protocols - on different layers of OSI model”