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Glossary of Terms
Posted by SteveT on Sunday, February 03, 2008 :: Last Updated on Sunday, February 03, 2008:: Views 3028

Term

Definitions

Authentication

A device used in network access control. It stores the usernames and passwords that identify the clients logging on, or it may hold the algorithms for token access. For access to specific network resources, the server may itself store user permissions and company policies or provide access to directories that contain the information

DNS

Domain Name System. The name resolution system that lets users locate computers on a Unix network or the Internet (TCP/IP network) by domain name. The DNS server maintains a database of domain names (host names) and their corresponding IP addresses. In this hypothetical example, if www.mycompany.com were presented to a DNS server, the IP address 204.0.8.51 would be returned. DNS has replaced the manual task of updating HOSTS files in an in house Unix network, and of course, it would be impossible to do this manually on the global Internet, given its size.

For Windows networks using TCP/IP, the counterpart to DNS is WINS. In a Windows NT or 9x – only network, only WINS needs to be used. In a Windows 2000 or .NET environment, DNS must be used.

In a mixed Windows/Unix environment, the Microsoft DNS server integrates the two. When a Unix station wants to resolve the name for a PC, it queries the Microsoft DNS server, which in turn queries the WINS server if it does not already have it.

DNSBL

Domain Name Service – based Block

Dotted Decimal Notation

See IP Address

DUN

Dial Up Networking. The dial – up networking capability in Microsoft^® Windows™

ESMTP

Extended SMTP (ESMTP) is a definition of protocol extensions to the Simple Mail Transfer Protocol standard. The extension format was defined in RFC 1869 in 1995.

RFC 1869 established a structure for all existing and future extensions, to produce a consistent and manageable means by which ESMTP clients and servers can be identified and ESMTP servers can indicate supported extensions to connected clients.

The main identification feature is for ESMTP clients to open a transmission with the command EHLO (Extended HELLO), rather than HELO (Hello, the original RFC 821 standard). A server can then respond with success (code 250), failure (code 550) or error (code 500, 501, 502, 504, or 421), depending on its configuration. An ESMTP server would return the code 250 OK in a multi – line reply with its domain and a list of keywords to indicate supported extensions. An RFC 821 compliant server would return error code 500, allowing the ESMTP client to try either HELO or QUIT.

Each service extension is defined in an approved format in subsequent RFCs and registered with the IANA. The first definitions were the RFC 821 optional services – SEND, SOML (Send or Mail), SAML (Send and Mail), EXPN, HELP, and TURN. The format of additional SMTP verbs was set and for new parameters in MAIL and RCPT.

With RFC 821 made obsolete by RFC 2821 in 2001 the ESMTP format was restated in RFC 2821. Support for the EHLO command in servers was made a "MUST," superceding the original HELO, which became a required "fallback." Non – standard, unregistered, service extensions can be used by bilateral agreement, these services are indicated by an EHLO keyword starting with "X," and with any additional parameters or verbs similarly marked.

FQDN

Fully Qualified Domain Name

FQHN

Fully Qualified Host Name

HTTP

Hyper Text Transfer Protocol. A protocol used to request and transmit files, especially web pages and web page components, over the Internet or other computer network.

IETF

Internet Engineering Task Force

IIS

Internet Information Services. Microsoft's Web server. IIS runs under the server versions of NT and 2000, adding full HTTP capability to the Windows operating system. Formerly known as "Internet Information Server," IIS is also available for the Windows 2000 client version

IMAP

Internet Message Access Protocol. The Internet Message Access Protocol (commonly known as IMAP, and previously called Interactive Mail Access Protocol) is an application layer Internet protocol used for accessing email on a remote server from a local client. IMAP and POP3 (Post Office Protocol version 3) are the two most prevalent Internet standard protocols for email retrieval.

IP Address

Internet Protocol address - The address of a computer attached to an IP network (TCP/IP network). Every client and server station must have a unique IP address. Client workstations have either a permanent address or one that is dynamically assigned to them when booted. IP addresses are written as four sets of numbers separated by periods; for example, 204.171.64.2. This is called "dotted decimal" notation.

The IP packet uses 32 bits each for source and destination addresses, and the 32 bits are made up of a network and host address. The more bits used for network address, the fewer remain for hosts. The following table shows how the 32 bits are divided between networks and hosts. The host bits are further subdivided between subnets and hosts (see subnet mask). Note that the next IP addressing scheme (IPv6) increases the address to 128 bits (see IPv6) for virtually an unlimited number of unique addresses.

IP addresses have traditionally been classified as Class A, B or C networks. Although the computer identifies the class by the first three bits of the address (A=0; B=10; C=110), people identify the class by the first number in the address (see number range below). This class – based system has also been greatly expanded, eliminating the huge disparity in the number of hosts that each class can accommodate.

Class	Number Range	Maximum Networks	Maximum Hosts	Bits used in NetID/HostID
A	1 – 126	127	16,777,214	7/24
	127	Reserved for loop back test
B	128 – 191	16,383	65,534	14/16
C	192 – 223	2,097,151	254	21/8

Networks, Subnets and Hosts

An IP address is first divided between networks and hosts. The host bits are further divided between subnets and hosts. See subnet mask

IP – Logical or Physical?

An IP address is somewhat of a hybrid, which can be thought of as either logical or physical, depending on how you view it. It is a unique number assigned to a node, which makes it seem physical, especially because there is so much name – to – IP address resolution going on in the network. There is also the Ethernet address, which is built into the network adapter. That is indeed physical, and it does not change, which is very typical of physical device names. However, since IP addresses can be dynamically assigned, causing the same client workstation to have a different IP address every day, the IP address seems more like a logical address. Regardless of what it is, it would make a great debate in a computer science class.

ISP

Internet Service Provider

L2TP

Layer 2 Tunneling Protocol. A protocol from the IETF that allows a PPP session to travel over multiple links and networks. L2TP is used to allow remote users access to the corporate network. PPP is used to encapsulate IP packets from the user's PC to the ISP, and L2TP extends that session across the Internet. L2TP was derived from Microsoft's Point – to – Point Tunneling Protocol (PPTP) and Cisco's Layer 2 Forwarding (L2F) technology.

LAN

Local Area Network. A system that links together electronic office equipment, such as computers and word processors, and forms a network within an office or building.

MAPS

Mail Abuse Prevention System. A California – based non – profit organization dedicated to eliminating spamming by maintaining the RBL (Realtime Blackhole List). The RBL contains the IP addresses of spammers, and companies and ISPs can use the list to reject incoming mail. If an offending spammer cannot be shut down, the spammer's ISP may contact MAPS with the subnet addresses allocated to the spammer so those specific addresses may be used instead of the IP address of the entire ISP. For information, visit http://mail – abuse.org

Multi – Homed

Having two or more network connections (network addresses). Servers often have two or more network adapters (NICs) to improve performance on the network. A server may also be connected to different networks; for example, to a serial line and a LAN or to two different LANs. In order to provide fault tolerance, a Web server is often connected to two different ISPs

MX Record

Mail Exchange Record. An MX record or Mail exchange record is a category of data in the Domain Name System specifying how Internet e – mail should be routed.

When an e – mail message is sent through the Internet, the sending mail transfer agent makes a DNS query requesting the MX record for the recipient's domain name, which is the portion of the e – mail address following the "@". This query returns a list of host names of mail exchange servers accepting incoming mail for that domain, together with a distance for each. The sending agent then attempts to establish an SMTP connection to one of these servers, starting with the one with the shortest distance, delivering the message to the first server with which a connection can be made. If no names were returned, a second request is made for the A record of the domain instead.

The MX mechanism provides the ability to run multiple mail servers for a single domain, both increasing the likelihood that mail may be delivered, and providing the ability to distribute the processing of incoming mail across multiple physical servers

Network Adapter

A printed circuit board that plugs into the bus of both the client machines and servers in a network. The network adapter controls the transmission and receiving of data at the data link level (OSI layers 1 and 2). It is also commonly called a "network interface card" (NIC).

A transmission medium, such as twisted pair or fiber – optic cable, connects the adapters to network hubs or switches, or in the case of a bus network, to each other. If no other network technology is mentioned, the terms "network adapter," "NIC," "network ready" or "LAN ready," imply Ethernet. Token Ring and LocalTalk networks have also been widely used from time to time, but Ethernet "is" the standard. Desktop computers often have Ethernet built into the motherboard and obviate the need for an Ethernet card to be plugged in.

NIC

Network Interface Card. Same as network adapter.

Open Relay

Typically refers to an e – mail server (SMTP server) that is configured to deliver any incoming mail to another mail server. In the past, open relays (open relay servers) were common, but today, most e – mail servers block all e – mail that does not originate with the customers of the service or employees of the company. The term may also apply to a proxy server that can be used by the general public.

Phishing

Pronounced "fishing," it is a scam to steal valuable information such as credit cards, social security numbers, user IDs and passwords. Also known as "brand spoofing," an official – looking e – mail is sent to potential victims pretending to be from their ISP, retail store, etc., and that due to internal accounting errors or some other pretext, certain information must be updated to continue the service.

A link in the e – mail message directs the user to a Web page that asks for financial information. The page looks genuine, because it is easy to fake a valid Web site. Any HTML page on the Web can be copied and modified to suit the phishing scheme. Such e – mails can be sent to people on selected lists or to any list, expecting that some percentage of the recipients will actually have an account with the real organization. The term comes from "fishing," where bait is used to catch a fish. In phishing, e – mail is the bait.

A "phishing kit" is a set of software tools that help the novice phisher imitate a target Web site and make mass mailings. It may even include lists of e – mail addresses. How thoughtful of people to create these kits. So helpful.

POP3

Post Office Protocol 3. A standard interface between an e – mail client program and the mail server. POP3 and IMAP4 are the two common access protocols used for Internet e – mail. POP3 provides a message store that holds incoming e – mail until users log on and download it.

POP3 is a simple system with limited selectivity. All pending messages and attachments are downloaded when users check their mail.

RADIUS

Remote Authentication Dial – In User Service. The de facto standard protocol for authentication servers (AAA servers). Developed by Livingston Enterprises (later acquired by Lucent), RADIUS uses a challenge/response method for authentication.

RBL

Realtime Blackhole List. A list of the IP addresses of known spammers. See MAPS.

SMTP

Simple Mail Transfer Protocol. The standard e – mail protocol on the Internet and part of the TCP/IP protocol suite. SMTP defines the message format and the message transfer agent (MTA), which stores and forwards the mail. SMTP was originally designed for only plain text (ASCII text), but MIME and other encoding methods enable executable programs and multimedia files to be attached to and transported with the e – mail message.

SMTP servers route SMTP messages throughout the Internet to a mail server that provides a message store for incoming mail. The mail server uses the POP3 or IMAP4 access protocol to communicate with the user's e – mail program. See POP3, IMAP4, MIME, SMTPi and messaging system.

SPF

Sender Policy Framework. An extension to the SMTP mail protocol on the Internet that verifies that a message is truly coming from the domain name indicated in the From field. It is designed to filter out messages from spammers and phishers who falsify the From address in the e – mail header. For more information, visit http://www.openspf.org/

Subnet Mask

SUBNET work mask. The technique used by the IP protocol to determine which network segment packets is destined for. The subnet mask is a binary pattern that is stored in the client machine, server or router and is matched with the IP address.

Depending on the network class (A, B or C), some number of bits are reserved for hosts and subnets, and these bits become a tradeoff. The more hosts, the fewer the subnets can be created; the more subnets, the fewer the hosts can be individually addressed.

The subnet mask below is a Class C address, which uses the first 24 bits for network ID and the last 8 for host ID. These last 8 can be divided between hosts and subnets. In the default mask below, the 0 means there are no subnets and up to 254 hosts can be addressed. In the second example, the 224 reserves the three high – order bits of that field for subnets, leaving the remaining 5 bits for hosts. This 224 pattern creates subnets in the range of 001 to 110 (000 and 111 are reserved). As such, 6 subnets of up to 30 hosts in the range of 00001 to 11110 can be addressed. Once again, 00000 and 11111 are reserved: all zeros mean "this" node, and all ones mean "all" nodes (broadcast), which is why calculations for maximum hosts and subnets are always subtracted by 2. For a list of all Class B and C subnet masks, see subnet mask tables.

Class C Default Submask
255.255.255.0
11111111.11111111.11111111.00000000

Class C Subnet Mask (6 Subnets of 30 Hosts Each)
255.255.255.224
11111111.11111111.11111111.11100000

Subnet Mask Tables

Following is a list of all Class B and C subnet masks and their maximum hosts and subnets. The last two octets (16 bits) of Class B and the last octet (8 bits) of Class C addresses are divided between hosts and subnets.

CLASS B SUBNET MASKS
SubnetMask	How 16 Bits Are Divided	Maximum Subnets	Maximum Hosts
255.255.192.0	2/14	2	16,382
255.255.224.0	3/13	6	8,190
255.255.240.0	4/12	14	4,094
255.255.248.0	5/11	30	2,046
255.255.252.0	6/10	62	1,022
255.255.254.0	7/9	126	510
255.255.255.0	8/8	254	254
255.255.255.128	9/7	510	126
255.255.255.192	10/6	1,022	62
255.255.255.224	11/5	2,046	30
255.255.255.240	12/4	4,094	14
255.255.255.248	13/3	8,190	6
255.255.255.252	14/2	16,382	2
CLASS C SUBNET MASKS
Subnet Mask	How 8 Bits Are Divided	Maximum Subnets	Maximum Hosts
255.255.255.192	2/6	2	62
255.255.224.224	3/5	6	30
255.255.240.240	4/4	14	14
255.255.248.248	5/3	30	6
255.255.252.252	6/2	62	2

TCP/IP

Transmission Control Protocol/Internet Protocol. A protocol for communication between computers, used as a standard for transmitting data over networks and as the basis for standard Internet protocols.

Top – Level Domain

An organization's unique name on the Internet. The chosen name combined with a top – level domain (TLD), such as .com or .org, makes up the Internet domain name.

TOS

WAN

Wide Area Network. A communications network that uses such devices as telephone lines, satellite dishes, or radio waves to span a larger geographic area than can be covered by a LAN.

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