Network Glossary M

Management Information Base The definitions for a particular set of data variables, with those definitions following the SMI specifications. See also SMI.

man-in-the-middle attack A characterization of a network attack in which packets flow to the attacker, and then out to the true recipient. As a result, the user continues to send data, increasing the chance that the attacker learns more and better information.

map class An FRTS configuration construct, configured with the map-class frame-relay global configuration command.

mark probability denominator Used by WRED to calculate the maximum percentage of packets discarded when the average queue depth falls between the minimum and maximum thresholds.

marking down Jargon referring to a policer action through which, instead of discarding an out-of-contract packet, the policer marks a different IPP or DSCP value, allowing the packet to continue on its way, but making the packet more likely to be discarded later.

MaxAge An OSPF timer that determines how long an LSA can remain in the LSDB without having heard a reflooded copy of the LSA.

Maxage timer An STP timer that dictates how long a switch should wait when it ceases to hear Hellos.

maximum reserved bandwidth A Cisco IOS interface setting, as a percentage between 1 and 99, that defines how much of the interface’s bandwidth setting may be allocated by a queuing tool. The default value is 75 percent.

Maximum Response Time After a host receives an IGMP Query, the amount of time (default, 10 seconds) the host has to send the IGMP Report.

Maximum Segment Size A TCP variable that defines the largest number of bytes allowed in a TCP segment’s Data field. The calculation does not include the TCP header. With a typical IP MTU of 1500 bytes, the resulting default MSS would be 1460. TCP hosts must support an MSS of at least 536 bytes

maximum threshold WRED compares this setting to the average queue depth to decide whether packets should be discarded. All packets are discarded if the average queue depth rises above this maximum threshold.

maximum transmission unit An IP variable that defines the largest size allowed in an IP packet, including the IP header. IP hosts must support an MTU of at least 576 bytes.

MD5 See Message Digest 5.

MD5 hash A term referring to the process of applying the Message Digest 5 (MD5) algorithm to a string, resulting in another value. The original string cannot be easily computed even when the hash is known, making this process a strong method for storing passwords.

MDRR See Modified Deficit Round-Robin.

Measured Round-Trip Time A TCP variable used as the basis for a TCP sender’s timer defining how long it should wait for a missing acknowledgement before resending the data.

Message Digest 5 A method of applying a mathematical formula, with input including a private key, the message contents, and sometimes a shared text string, with the resulting digest being included with the message. The sender and the receiver perform the same math to allow authentication and to prove that no intermediate device changed the message contents.

metric With routing protocols, the measurement of favorability that determines which entry will be installed in a routing table if more than one router is advertising that exact network and mask.

MIB See Management Information Base.

MIB walk In SNMP, the process of a manager using successive GetNext and GetBulk commands to discover the exact MIB structure supported by an SNMP agent. The process involves the manager asking for each successive MIB leaf variable.

MIB-I The original standardized set of generic SNMP MIB variables, defined in RFC 1158.

MIB-II The most recent standardized set of generic SNMP MIB variables, defined in RFC 1213 and updated in RFCs 2011 through 2013.

mincir See minimum CIR.

minimum CIR Jargon referring to the minimum value to which adaptive shaping will lower the shaping rate.

minimum threshold WRED compares this setting to the average queue depth to decide whether packets should be discarded. No packets are discarded if the average queue depth falls below this minimum threshold.

MLD See Multicast Listener Discovery.

MLP See Multilink PPP.

MLP LFI The PPP function for fragmenting packets, plus interleaving delay-sensitive later-arriving packets between the fragments of the first packet.

MLS See Multilayer Switching.

Modified Deficit Round-Robin A Cisco 12000 series router feature that combines the key features of LLQ and CQ to provide similar congestion-management features.

modified tail drop A WFQ term referring to its drop logic, which is similar to tail-drop behavior.

Modular QoS CLI The common set of IOS configuration commands that is used with each QoS feature whose name begins with “Class-Based.”

MOSPF See Multicast Open Shortest Path First.

MPD See mark probability denominator.

MPLS Experimental (EXP) A 3-bit field in an MPLS header used for marking frames.

MPLS TTL propagation The MPLS feature by which an ingress E-LSR copies the IP packet’s IP TTL field into the MPLS header’s TTL field.

MPLS unicast IP routing The simplest MPLS application, involving the advertisement of an IGP to learn IP routes, and LDP or TDP to advertise labels.

MPLS VPNs An MPLS application that allows the MPLS network to connect to multiple different IP networks, with overlapping IP addresses, and provide IP connectivity to those multiple networks.

MQC See Modular QoS CLI.

MRT See Maximum Response Time.

MRTT See Measured Round-Trip Time.

MSS See Maximum Segment Size.

MST See Multiple Spanning Trees.

MTU See maximum transmission unit.

MULTI_EXIT_DISC (MED) A BGP path attribute that allows routers in one AS to set a value and advertise it into a neighboring AS, impacting the decision process in that neighboring AS. A smaller value is considered better. Also called the BGP metric.

multi-action policing In MQC and CB Policing, a configuration style by which, for one category of packets (conform, exceed, or violate), more than one marking action is defined for a single category. For example, marking DSCP and DE.

multicast A type of IPv4 and IPv6 traffic designed primarily to provide one-to-many connectivity but unlike broadcast, has the capability to control the scope of traffic distribution.

multicast IP address range IP multicast address range from 224.0.0.0 through 239.255.255.255.

multicast IP address structure The first 4 bits of the first octet must be 1110. The last 28 bits are unstructured.

Multicast Listener Discovery The IPv6 protocol used for the discovery of which hosts are listening for which multicast IP addresses for IPv6.

multicast MAC address A 48-bit address that is calculated from a Layer 3 multicast address by using 0x0100.5E as the multicast vendor code (OUI) for the first 24 bits, always binary 0 for the 25th bit, and copying the last 23 bits of the Layer 3 multicast address.

Multicast Open Shortest Path First A multicast routing protocol that operates in dense mode and depends on the OSPF unicast routing protocol to perform its multicast functions.

multicast scoping The practice of defining boundaries that determine how far multicast traffic will travel in your network.

multicast state information The information maintained by a router for each multicast entry in its multicast routing table, such as incoming interface, outgoing interface list, Uptime timer, Expire timer, etc.

multicasting Sending a message from a single source or multiple sources to selected multiple destinations across a Layer 3 network in one data stream.

Multilayer Switching A process whereby a switch, when making a forwarding decision, uses not only Layer 2 logic but other OSI layer equivalents as well.

Multilink PPP A PPP feature used to load balance multiple parallel links at Layer 2 by fragmenting frames, sending one frame over each of the links in the bundle, and reassembling them at the receiving end of the link.

multipath An issue whereby parts of the RF signal take different paths from the source to the destination, which causes direct and reflected signals to reach the receiver at different times, and corresponding bit errors.

Multiple Spanning Trees Defined in IEEE 802.1s, a specification for multiple STP instances when using 802.1Q trunks.