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A+ Study Guide: Domain 5.0: Networks - Protocols

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TCP/IP Protocol Suite
TCP/IP Ports
TCP/IP Addressing

The function of a network is to share resources between computers. In order for this to happen the computers must be able to "talk" to each other which is accomplished with the use of protocols which are essentially a set of "rules" that govern communication over a network. Computers must be configured with a common protocol in order to be able to communicate. Below are some of the most common protocols:
  • TCP/IP - TCP/IP is the most commonly used protocol today. It is the one used on the internet and most other networks. It will be covered in the next sections.
  • IPX/SPX - These protocols were developed by Novell and are/were used with Novell Netware. IPX is the fastest routable protocol and is not connection oriented. IPX addresses are up to 8 characters in hexadecimal format. SPX is connection oriented.
  • NWLink - Microsoft's implementation of the Novell NetWare IPX/SPX protocol for Windows NT Server and Workstation. Not very common anymore.
  • NetBeui - Stands for "NetBIOS Extended User Interface". It was the standard protocol used by older Microsoft operating systems. It is NetBEUI that allowed the "shares' between machines. In reference to the NetBIOS distinction, NetBIOS is the applications programming interface and NetBEUI is the transport protocol. NetBEUI is a non-routable protocol meaning it will not allow communication through a router. This protocol is not used much anymore.
TCP/IP Protocol Suite:
The TCP/IP protocol suite is made of many other protocols that perform different functions. Below is a list of some of them:
  • TCP - TCP breaks data into manageable packets and tracks information such as source and destination of packets. It is able to reroute packets and is responsible for guaranteed delivery of the data.
  • IP - This is a connectionless protocol, which means that a session is not created before sending data. IP is responsible for addressing and routing of packets between computers. It does not guarantee delivery and does not give acknowledgement of packets that are lost or sent out of order as this is the responsibility of higher layer protocols such as TCP.
  • ICMP - Internet Control Message Protocol enables systems on a TCP/IP network to share status and error information such as with the use of PING and TRACERT utilities.
  • SMTP - Used to reliably send and receive mail over the Internet.
  • FTP - File transfer protocol is used for transferring files between remote systems. Must resolve host name to IP address to establish communication. It is connection oriented (i.e. verifies that packets reach destination).
  • ARP - provides IP-address to MAC address resolution for IP packets. A MAC address is your computer's unique hardware number and appears in the form 00-A0-F1-27-64-E1 (for example). Each computer stores an ARP cache of other computers ARP-IP combinations.
  • POP3 - Post Office Protocol. A POP3 mail server holds mail until the workstation is ready to receive it.
  • TELNET - Provides a virtual terminal or remote login across the network that is connection-based. The remote server must be running a Telnet service for clients to connect.
  • HTTP - The Hypertext Transfer Protocol is the set of rules for exchanging files (text, graphic images, sound, video, and other multimedia files) on the World Wide Web. It is the protocol controlling the transfer and addressing of HTTP requests and responses.
TCP/IP Ports:
Ports are what an application uses when communicating between a client and server computer. Some common ports are:
  • 21 FTP
  • 23 TELNET
  • 25 SMTP
  • 80 HTTP
  • 110 POP3
TCP/IP Addressing:
Every IP address can be broken down into 2 parts, the Network ID(netid) and the Host ID(hostid). All hosts on the same network must have the same netid. Each of these hosts must have a hostid that is unique in relation to the netid. IP addresses are divided into 4 octets with each having a maximum value of 255. We view IP addresses in decimal notation such as, but it is actually utilized as binary data.

IP addresses are divided into 3 classes as shown below:

Class Range
A 1-126
B 128-191
C 192-223

NOTE: 127.x.x.x is reserved for loopback testing on the local system and is not used on live systems. The following address ranges are reserved for private networks: - - -

The previous information on TCP/IP has referred to IPv4, however, this addressing scheme has run out of available IP addresses due to the large influx of internet users and expanding networks. As a result, the powers that be had to create a new addressing scheme to deal with this situation and developed IPv6. This new addressing scheme utilizes a 128 bit address (instead of 32) and utilizes a hex numbering method in order to avoid long addresses such as The hex address format will appear in the form of 3FFE:B00:800:2::C for example.

VOIP (Voice Over Internet Protocol) - Also known as Internet Telephony, VOIP is the technology that allows voice traffic to be transmitted and routed over a data network using the Internet Protocol. The advantage of VOIP is that it is low cost (in some cases free) in comparison to using tradition POTS (Plain Old Telephone Systems) for voice communications. Companies such as Vonage and Comcast Cable are currently offering VOIP phone services and Skype is a freeware program that provides free long distance communications with other Skype users.

Further Reference: Networking Tutorials