Table 2-6 Ports and Protocols

Protocol Name	Port Number	Use
POP3		Email (incoming)
IMAP		Email (incoming)
SMTP		Email outgoing to a server or between email serv-
		ers, not from server to client
SSH		Secure remote access via the command-line inter-
		face (CLI)
Telnet		Unsecure remote access via the CLI
FTP		Downloading files
HTTP		Hypertext Transfer Protocol, connection to unsecure
		website
HTTPS		Secure HTTP, connections to secure websites
DNS		Friendly URL names
RDP		Remote Desktop Protocol; used for Windows
		Remote Desktop Connection

DNS

The Domain Name System (DNS) is the name for the network of servers on the Internet that trans-late domain names, such as www.informit.com, and individual hostnames into their matching IP addresses. If you manually configure an IP address, you usually provide the IP addresses of one or more DNS servers as part of the configuration process.

A domain name has three major sections, from the end of the name to the start:

The top-level domain (.com, .org, .net, and so on). The name of the site.

The server type. www indicates a web server, ftp indicates an FTP server, mail indicates a mail server, and search indicates a search server.

Chapter 2: Networking 49

DHCP

The Dynamic Host Configuration Protocol (DHCP) is used to automatically assign IP addresses to hosts (printers, routers, computers, and so on). In most SOHO networks, a router uses DHCP to assign IP addresses to the client computers. However, your ISP will also use DHCP to assign an IP address to you; usually your router gets this.

LDAP

Lightweight Directory Access Protocol (LDAP) is used to access and maintain distributed directo-ries of information (directory services) such as the kind involved with Microsoft domains.

SNMP

Simple Network Management Protocol (SNMP) is used as the standard for managing and monitor-ing devices on your network. It manages routers, switches, and computers and is often incorpo-rated in software known as a network management system (NMS).

SMB

The Server Message Blocks (SMB) protocol provides access to shared items such as files and printers.

SSH

Secure Shell (SSH) allows data to be exchanged between computers on a secured channel. This protocol offers a more secure replacement to FTP and Telnet. The Secure Shell server housing the data you want to access would have port 22 open.

SFTP

Secure FTP (SFTP). Provides file access over a reliable data stream that is generated and protected by SSH.

TCP Versus UDP

Transmission Control Protocol (TCP) sessions are known as connection-oriented sessions. This means that every packet that is sent is checked for delivery. If the receiving computer doesn’t receive a packet, it cannot assemble the message, and will ask the sending computer to transmit the packet again. No one packet is left behind.

User Datagram Protocol (UDP) sessions are known as connectionless sessions. UDP is used in streaming media sessions. In these cases, if a packet is dropped, it is not asked for again.

50 CompTIA A+ Quick Reference

Wireless Networks

All Wi-Fi standards for the A+ exams are defined by IEEE 802.11. The four standards are a, b, g, and n. The a standard is not compatible with any of the others and has a small range of 150 feet. The b and g standards are interoperable, and n works with both b and g. Table 2-7 summarizes what is different among those four versions.