Protocols
Lightweight Directory Access Protocol (LDAP)
LDAP is a protocol used to access information about network resources stored by a directory service, such as Active Directory or eDirectory. LDAP uses ports 389 (clear text) and 636 (secure).
Remote Desktop Protocol (RDP)
RDP allows you to view and use the graphical desktop of a remote computer system as if you were sitting in front of it. RDP uses port 3389 by default.
Remote Terminal Emulation (Telnet)
Telnet allows an attached computer to act as a dumb terminal, with data processing taking place on the IP host computer. It is still widely used to provide connectivity between dissimilar systems. Telnet can also be used to test a service by the use of HTTP commands. You should avoid using Telnet as it transmits all data, including usernames and passwords clear text. Telnet uses port 23 by default.
Secure FTP (SFTP)
SFTP addresses one of the key weaknesses of FTP; namely, FTP doesn't use encryption. All data, including user names and passwords, is sent clear text. SFTP provides the same functionality as FTP, but secures the data transmissions using the SSH protocol. SFTP uses port 22, the same port used by SSH.
Server Message Block (SMB)
SMB enables the sharing of folders and printers on the network. Using SMB, remote users can access files in a shared folder on a server or workstation. Likewise, a remote user can send print jobs to a shared printer. SMB is also known as Common Internet File System (CIFS). SMB uses ports 137, 138, and 139.
Simple Mail Transfer Protocol (SMTP)
SMTP is used to route electronic mail through the internetwork. E-mail applications provide the interface to communicate with SMTP or mail servers. SMTP uses port 25 by default.
Simple Network Management Protocol (SNMP)
SNMP is used to monitor and manage network devices. SNMP agents can be installed on network devices such as PCs, switches, and routers. These agents send data to an SNMP manager application running on an administrative workstation, which aggregates the information and displays an overview of the current network status. Thresholds can be configured which trigger alerts if exceeded. SNMP uses ports 161 and 162.
Secure Shell (SSH)
SSH allows for secure interactive control of remote systems. SSH is much more secure alternative to Telnet. SSH uses port 22 by default.
Dynamic Host Configuration Protocol (DHCP)
DHCP is used to dynamically assign IP addressing information to network hosts when they come online. The client system, when it connects to the network, broadcasts a DHCPDISCOVER message on the network, looking for a DHCP server. The DHCP server responds with a DHCPOFFER message containing proposed IP addressing configuration information. The client then responds with a DHCPREQUEST message to the DHCP server indicating it wants to use the proposed configuration. The DHCP server makes the assignment with a DHCPACK message. DHCP uses ports 67 and 68.
Domain Name System (DNS)
DNS is a system that is distributed throughout the internetwork to provide address/name resolution. For example, the name www.mydomain.com would be identified with a specific IP address. DNS uses port 53 by default.
File Transfer Protocol (FTP)
FTP provides a generic method of transferring files. It can include file security through usernames and passwords, and it allows file transfer between dissimilar computer systems. FTP can transfer both binary and text files, including HTML, to another host. FTP URLs are preceded by ftp:// followed by the DNS name of the FTP server. To log in to an FTP server, use: ftp://username@servername. FTP uses ports 20 and 21 by default.
HyperText Transfer Protocol (HTTP)
HTTP is used by Web browsers and Web servers to exchange files (such as Web pages) through the World Wide Web and intranets. HTTP can be described as an information requesting and responding protocol. It is typically used to request and send Web documents, but is also used as the protocol for communication between agents using different IP protocols. HTTP uses port 80 by default.
HyperText Transfer Protocol over Secure Socket Layer or HTTP over SSL (HTTPS)
HTTPS is a secure form of HTTP that uses SSL as a sublayer for security. SSL secures messages being transmitted on the Internet. It uses RSA for authentication and encryption. Web browsers use SSL (Secure Sockets Layer) to ensure safe Web transactions. URLs that begin with https:// trigger your Web browser to use SSL. HTTPS uses port 443 by default.
Internet Message Access Protocol (IMAP)
IMAP is an e-mail retrieval protocol designed to enable users to access their e-mail from various locations without the need to transfer messages or files back and forth between computers. Messages remain on the remote mail server and are not automatically downloaded to a client system. IMAP uses port 143 by default.
Post Office Protocol 3 (POP3)
POP3 is part of the IP protocol suite and used to retrieve e-mail from a remote server to a local client over an IP connection. With POP3, e-mail messages are downloaded to the client. POP3 uses port 110 by default.
