Media Access Control layer. One of two sub-layers that make up the Data Link Layer of the OSI model. The MAC layer is responsible for moving data packets to and from one NIC to another across a shared channel.

MAC address

Media access control address. The MAC address, sometimes known as the hardware address, is the unique physical address of each network interface card on each device.


Metropolitan area network. A MAN is a data network designed for a town or city. MANs may be operated by one organization such as a corporation with several offices in one city, or be shared resources used by several organizations with several locations in the same city. MANs are usually characterized by very high-speed connections.

master node

In EAPS, the master node is a switch, or node, that is designated the master in an EAPS domain ring. The master node blocks the secondary port for all non-control traffic belonging to this EAPS domain, thereby avoiding a loop in the ring.

master router

In VRRP, the master router is the physical device (router) in the VRRP virtual router that is responsible for forwarding packets sent to the VRRP virtual router and for responding to ARP requests. The master router sends out periodic advertisements that let backup routers on the network know that it is alive. If the VRRP IP address owner is identified, it always becomes the master router.

master VLAN

In ESRP, the master VLAN is the VLAN on the ESRP domain that exchanges ESRP-PDUs and data between a pair of ESRP-enabled devices. You must configure one master VLAN for each ESRP domain, and a master VLAN can belong to only one ESRP domain.


Multiple exit discriminator. BGP uses the MED metric to select a particular border router in another AS when multiple border routers exist.

member VLAN

In ESRP, you configure zero or more member VLANs for each ESRP domain. A member VLAN can belong to only one ESRP domain. The state of the ESRP device determines whether the member VLAN is in forwarding or blocking state.


In CFM, maintenance end point is an end point for a single domain, or maintenance association. The MEP may be either an UP MEP or a DOWN MEP.


In QoS, metering monitors the traffic pattern of each flow against the traffic profile. For out-of-profile traffic the metering function interacts with other components to either re-mark or drop the traffic for that flow. In the Extreme Networks implementation, you use ACLs to enforce metering.


Management Information Base. MIBs make up a database of information (for example, traffic statistics and port settings) that the switch makes available to network management systems. MIB names identify objects that can be managed in a network and contain information about the objects. MIBs provide a means to configure a network device and obtain network statistics gathered by the device. Standard, minimal MIBs have been defined, and vendors often have private enterprise MIBs.


Message Integrity Check or Code (MIC), also called ?Michael‘, is part of WPA and TKIP. The MIC is an additional 8-byte code inserted before the standard 4-byte integrity check value (ICV) that is appended in by standard WEP to the 802.11 message. This greatly increases the difficulty in carrying out forgery attacks. 
Both integrity check mechanisms are calculated by the receiver and compared against the values sent by the sender in the frame. If the values match, there is assurance that the message has not been tampered with. (See WPA, TKIP, and ICV.)


In CFM, the maintenance intermediate point is intermediate between endpoints. Each MIP is associated with a single domain, and there may be more than one MIP in a single domain.


Port mirroring configures the switch to copy all traffic associated with one or more ports to a designated monitor port. The monitor port can be connected to an network analyzer or RMON probe for packet analyzer.


Multi-switch Link Aggregation Group (a.k.a. Multi-Chassis Link Aggregation Group). This feature allows users to combine ports on two switches to form a single logical connection to another network device. The other network device can be either a server or a switch that is separately configured with a regular LAG (or appropriate server port teaming) to form the port aggregation.


Management Module. For more information, see "Management Modules" in the ExtremeSwitching X8 Series Switches Hardware Installation Guide.


Multimode fiber. MMF is a fiber optic cable with a diameter larger than the optical wavelength, in which more than one bound mode can propagate. Capable of sending multiple transmissions simultaneously, MMF is commonly used for communications of 2 km or less.


Multicast Source Discovery Protocol. MSDP is used to connect multiple multicast routing domains. MSDP advertises multicast sources across Protocol Independent Multicast-Sparse Mode (PIM-SM) multicast domains orRendezvous Points (RPs). In turn, these RPs run MSDP over TCP to discover multicast sources in other domains.


Master Switch Fabric Module. This Extreme Networks-proprietary name refers to the module that holds both the control plane and the switch fabric for switches that run the ExtremeXOS software on modular switches. One MSM is required for switch operation; adding an additional MSM increases reliability and throughput. Each MSM has two CPUs. The MSM has LEDs as well as a console port, management port, modem port, and compact flash; it may have data ports as well. The MSM is responsible for upper-layer protocol processing and system management functions. When you save the switch configuration, it is saved to all MSMs.


Multiple Spanning Tree Instances. MSTIs control the topology inside an MSTP region. An MSTI is a spanning tree domain that operates within a region and is bounded by that region; and MSTI does not exchange BPDUs or send notifications to other regions. You can map multiple VLANs to an MSTI; however, each VLAN can belong to only one MSTI.You can configure up to 64 MSTIs in an MSTP region.

MSTI regional root bridge

In an MSTP environment, each MSTI independently elects its own root bridge. The bridge with the lowest bridge ID becomes the MSTI regional root bridge. The bridge ID includes the bridge priority and the MAC address.

MSTI root port

In an MSTP environment, the port on the bridge with the lowest path cost to the MSTI regional root bridge is the MSTI root port.


Multiple Spanning Tree Protocol. MSTP, based on IEEE 802.1Q-2003 (formerly known as IEEE 892.1s), allows you to bundle multiple VLANs into one spanning tree (STP) topology, which also provides enhanced loop protection and better scaling. MSTP uses RSTP as the converging algorithm and is compatible with legacy STP protocols.

MSTP region

An MSTP region defines the logical boundary of the network. Interconnected bridges that have the same MSTP configuration are referred to as an MSTP region. Each MSTP region has a unique identifier, is bound together by one CIST that spans the entire network, and contains from 0 to 64 MSTIs. A bridge participates in only one MSTP region at one time. An MSTP topology is individual MSTP regions connected either to the rest of the network with 802.1D and 802.1w bridges or to each other.


Maximum transmission unit. This term is a configurable parameter that determines the largest packet than can be transmitted by an IP interface (without the packet needing to be broken down into smaller units).


Packets that are larger than the configured MTU size are dropped at the ingress port. Or, if configured to do so, the system can fragment the IPv4 packets and reassemble them at the receiving end.


Multicast messages are transmitted to selected devices that specifically join the multicast group; the addresses are specified in the destination address field. In other words, multicast (point-to-multipoint) is a communication pattern in which a source host sends a message to a group of destination hosts.


IP multinetting assigns multiple logical IP interfaces on the same circuit or physical interface. This allows one bridge domain (VLAN) to have multiple IP networks.


Multicast VLAN registration. MVR allows a subscriber on a port to subscribe and unsubscribe to a multicast stream on the network-wide multicast VLAN; it allows the single multicast VLAN to be shared in the network while subscribers remain in separate VLANs. MVR provides the ability to continuously send multicast streams in the multicast VLAN, but to isolate the The application from the subscriber VLANs for bandwidth and security reasons. MVR allows a multicast stream received over a Layer 2 VLAN to be forwarded to another VLAN, eliminating the need for a Layer 3 routing protocol; this feature is often used for IPTV applications.