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Glossary: CCNA & General Networking Terms 


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See: Media Access Control
MAC address
The hardware address of a device connected to a shared media. See also: Media Access Control, Ethernet, token ring. [Source: MALAMUD]
mail bridge
A mail gateway that forwards electronic mail between two or more networks while ensuring that the messages it forwards meet certain administrative criteria. A mail bridge is simply a specialized form of mail gateway that enforces an administrative policy with regard to what mail it forwards. See also: Electronic Mail, mail gateway. [Source: NNSC]
Mail Exchange Record (MX Record)
A DNS resource record type indicating which host can handle mail for a particular domain. See also: Domain Name System, Electronic Mail. [Source: MALAMUD]
mail exploder
Part of an electronic mail delivery system which allows a message to be delivered to a list of addresses. Mail exploders are used to implement mailing lists. Users send messages to a single address and the mail exploder takes care of delivery to the individual mailboxes in the list. See also: Electronic Mail, email address, mailing list. [Source: RFC1208]
mail gateway
A machine that connects two or more electronic mail systems (including dissimilar mail systems) and transfers messages between them. Sometimes the mapping and translation can be quite complex, and it generally requires a store-and-forward scheme whereby the message is received from one system completely before it is transmitted to the next system, after suitable translations. See also: Electronic Mail. [Source: RFC1208]
mail path
A series of machine names used to direct electronic mail from one user to another. This system of email addressing has been used primarily in UUCP networks which are trying to eliminate its use altogether. See also: bang path, email address, UNIX-to-UNIX CoPy. [Source: RFC1392]
mail server
A software program that distributes files or information in response to requests sent via email. Internet examples include Almanac and netlib. Mail servers have also been used in Bitnet to provide FTP-like services. See also: Bitnet, Electronic Mail, FTP. [Source: NWNET]
mailing list
A list of email addresses, used by a mail exploder, to forward messages to groups of people. Generally, a mailing list is used to discuss certain set of topics, and different mailing lists discuss different topics. A mailing list may be moderated. This means that messages sent to the list are actually sent to a moderator who determines whether or not to send the messages on to everyone else. Requests to subscribe to, or leave, a mailing list should ALWAYS be sent to the list's "-request" address (e.g., for the IETF mailing list) or majordomo server. See also: Electronic Mail, mail exploder, email address, moderator, majordomo. [Source: RFC1983]
A program which handles mailing list maintenance (affectionately known as administrivia) such as adding and removing addresses from mailing lists. See also: email address, mailing list. [Source: RFC1983]
See: Metropolitan Area Network
Management Information Base (MIB)
The set of parameters an SNMP management station can query or set in the SNMP agent of a network device (e.g., router). Standard, minimal MIBs have been defined, and vendors often have Private enterprise MIBs. In theory, any SNMP manager can talk to any SNMP agent with a properly defined MIB. See also: client-server model, Simple Network Management Protocol, SMI. [Source: BIG-LAN]
Mail Abuse Prevention System.
A humorous term applied to packets that turn up unexpectedly on the wrong network because of bogus routing entries. Also used as a name for a packet which has an altogether bogus (non-registered or ill-formed) internet address. [Source: RFC1208]
MAU (1)
Multistation Access Unit, for connection and control of Token Ring network stations in a star arrangement. Also known as MSAU.
MAU (2)
Monitoring and Advisory Unit, a JISC-sponsored service to manage contracts between JISC and several JISC-funded services.
Maximum Transmission Unit (MTU)
The largest frame length which may be sent on a physical medium. See also: frame, fragmentation, frame. [Source: RFC1392]
Megabits (million - or strictly 2 to the power 20 - bits) per second.
The Multicast Backbone is based on IP multicasting using class-D addresses. The mbone concept was adopted at the March 1992 IETF in San Diego, during which it was used to audiocast to 40 people throughout the world. At the following meeting, in Cambridge, the name mbone was adopted. Since then the audiocast has become full two-way audio/video conferencing using two video channels, four audio channels, and involving hundreds of remote users. See also: multicast, Internet Engineering Task Force. [Source: RFC1983]
MD-2, MD-4, MD-5
See: Message Digest.
Media Access Control (MAC)
The lower portion of the datalink layer. The MAC differs for various physical media. See also: MAC Address, Ethernet, Logical Link Control, token ring. [Source: RFC1392]
The material used to support the transmission of data. This can be copper wire, coaxial cable, optical fibre, or electromagnetic wave (as in microwave).
Message Digest (MD-2, MD-4, MD-5)
Message digests are algorithmic operations, generally performed on text, which produce a unique signature for that text. MD-2, described in RFC 1319; MD-4, described in RFC 1320; and MD-5, described in RFC 1321 all produce a 128-bit signature. They differ in their operating speed and resistance to crypto-analytic attack. Generally, one must be traded off for the other. [Source: RFC1983]
message switching
See: packet switching
Metropolitan Area Network (MAN)
A data network intended to serve an area approximating that of a large city. Such networks are being implemented by innovative techniques, such as running fibre cables through subway tunnels. A popular example of a MAN is SMDS. See also: Local Area Network, Switched Multimegabit Data Service, Wide Area Network. [Source: NNSC]
Message Handling System. The system of message user agents, message transfer agents, message stores, and access units which together provide OSI electronic mail. MHS is specified in the CCITT X.400 series of Recommendations. [Source: RFC1208]
See: Management Information Base
Microcom Networking Protocol (MNP)
A series of protocols built into most modems which error-check or compress data being transmitted over a phone line. [Source: RFC1983]
See: Midlands JANET User Group
Midlands JANET User Group (MidJUG)
The Midlands JANET User Group presents the views of the users on JANET and UKERNA services to the JISC Committee on Networking through the JANET National User Group. See also: JANET National User Group.
mid-level network
Mid-level networks (a.k.a. regionals) make up the second level of the Internet hierarchy. They are the transit networks which connect the stub networks to the backbone networks. See also: backbone, Internet, stub network, transit network. [Source: RFC1392]
Midlands Metropolitan Area Network.
MILitary NETwork. Originally part of the ARPANET, MILNET was partitioned in 1984 to make it possible for military installations to have reliable network service, while the ARPANET continued to be used for research. See DDN. [Source: RFC1208]
See: Multipurpose Internet Mail Extensions
Microsoft Management Console.
See: Microcom Networking Protocol.
A person, or small group of people, who manage moderated mailing lists and newsgroups. Moderators are responsible for determining which email submissions are passed on to list. See also: Electronic Mail, mailing list, Usenet. [Source: RFC1392]
Multicast Open Shortest-Path First. See: Open Shortest-Path First. [Source: RFC1983]
Monitoring SubCommittee, a subcommittee of JCN to monitor the performance of JANET, now superseded by SPAG.
Message Transfer Agent. An OSI application process used to store and forward messages in the X.400 Message Handling System. Equivalent to Internet mail agent. [Source: RFC1208]
See: Maximum Transmission Unit
See: Multi-User Dungeon
A packet with a special destination address which multiple nodes on the network may be willing to receive. See also: broadcast, unicast. [Source: RFC1208]
multiCCNAd host
A host which has more than one connection to a network. The host may send and receive data over any of the links but will not route traffic for other nodes. See also: host, router. [Source: MALAMUD]
The division of a single transmission medium into multiple logical channels supporting many simultaneous sessions. For example, one network may have simultaneous FTP, telnet, rlogin, and SMTP connections, all going at the same time.
Multipurpose Internet Mail Extensions (MIME)
An extension to Internet email which provides the ability to transfer non-textual data, such as graphics, audio and fax. It is defined in RFC 1341. See also: Electronic Mail. [Source: RFC1392]
Multi-User Dungeon (MUD)
Adventure, role playing games, or simulations played on the Internet. Devotees call them "text-based virtual reality adventures". The games can feature fantasy combat, booby traps and magic. Players interact in real time and can change the "world" in the game as they play it. Most MUDs are based on the Telnet protocol. See also: Telnet. [Source: LAQUEY]
MX Record
See: Mail Exchange Record


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