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
NOTE: I recommend you download all the cheat sheets from the site here

Popular Protocols:

Port 21 – FTP – File Transfer Protocol
Port 22 – SSH/ SCP – Used for secure connections
Port 25 – SMTP –
Port 53 – DNS
Port 80 – HTTP – Protocol used to browse the web. More info here
Port 110 – POP3
Port 143- IMAP4
Port 161-162 – SNMP
Port 443 – HTTPS
Port 989-990 – FTP over SSL
Port 993 – IMAP4 over SSL
Port 995 – POP3 over SSL
This is not meant to be an all inclusive list, but here is a list of protocols per layer:

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

CDP Cisco Discovery Protocol
DCAP Data Link Switching Client Access Protocol
Dynamic Trunking Protocol
FDDI Fiber Distributed Data Interface
Frame Relay
HDLC High Level Data Link Control
IEEE 802.11
IEEE 802.16
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)
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
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