Glossary

# A C D E F G H I L M N O P Q R S T U V

 

802.1X. An IEEE standard that defines a client-server access-control and authentication protocol for restricting unauthorized devices from connecting to a LAN through publicly accessible ports.

Access Control List. See ACL.

ACP. Access Control Parameter. Synonym for mask.

Access List Element. See ACE.

access point. A device that serves as a center point in a wireless network or a connection point between wireless devices and a wired network.

access port. A port that carries the traffic of one virtual LAN (VLAN). Contrast with trunk port.

ACE. Access List Element. An element in an ACL that includes an action (permit or deny), a mask, and rules.

ACL. Access Control List. A list of one or more Access List Elements (ACEs), which collectively define the network traffic profile. ACLs can be used as security filters and traffic filters, or for policy-based routing, encryption, queuing, and traffic shaping.

address aggregation. A routing protocol feature that breaks major network addresses into aggregates representing numerically contiguous groups of addresses known as a supernets. This feature automatically suppresses the advertisement of more specific networks on a chosen interface.

administrative speed. The speed of a link as specified by the administrator. If the administrator specifies auto as the speed, the actual speed is determined through autonegotiation.

advertising. The router process of sending routing and service updates at intervals so that other routers can maintain a table of usable routes.

aggregate policer. A policer that applies its limits cumulatively to traffic in all the classes with which it is associated. For example, if an aggregate policer limits transmission rates to 1000 kbps and is used by three classes with a transmission rate of 400 kbps each, it will perform its exceed action because the cumulative transmission rate (3 x 400 kbps = 1200 kbps) exceeds 1000 kbps.

area. A group of adjacent routers that share OSPF link-state updates. It is identified by a number, an area ID.

autonegotiation. The ability of linked ports to determine each other's characteristics and choose the best communication method.

candidate switch. A device that is eligible to be a member switch.

CDP. Cisco Discovery Protocol. A protocol that a device uses to advertise its existence to other devices and to receive information about other devices on the same LAN or on the remote side of a WAN.

CGMP. Cisco Group Management Protocol. A protocol that reduces the flooding of IP multicast packets by limiting the transmission of these packets to clients that request them. End stations become clients by issuing join messages to join a CGMP group; they issue leave messages to leave the group.

child window. A configuration window that is launched by clicking a button in another configuration window. Contrast with parent window.

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Cisco Discovery Protocol. See CDP.

Cisco Group Management Protocol. See CGMP.

class. A group to which packets with a common characteristic belong. The characteristic can be a certain DSCP or IP precedence value, or something in the packet that matches a filtering criterion in a certain ACL.

class of service value. See CoS value.

cluster. A group of connected switches that is managed as a single entity. The switches can be in the same location, or they can be distributed across a contiguous network. All communication with cluster switches is through one IP address. See command switch and member switch.

Cluster Management Suite. See CMS.

CMS. Cluster Management Suite. An integrated set of web-based applications that is used to create clusters of switches, monitor real-time images of switches, and configure both clustered and standalone switches.

command switch. A switch that is used as a single point of access for managing, configuring, and monitoring the member switches of a cluster.

CoS value. class of service value. In an ISL frame, the three least significant bits in the User field. In an 802.1Q frame, the three User Priority bits.

CPE. customer premises equipment. A device that connects a computer or laptop to a Catalyst LRE switch by using Long-Reach Ethernet technology over ordinary telephone lines.

destination-based forwarding. The forwarding of a packet by a port group based on the packet's destination address. Contrast with source-based forwarding.

Differentiated Services Code Point value. See DSCP value.

distance-vector protocol. A type of routing protocol that maintains a list of the distance to another network in hops (number of routers crossed). RIPv2 and EIGRP are examples of this protocol type. Contrast with link-state protocol.

DSCP value. Differentiated Services Code Point value. In a packet, the six most significant bits of the 1-byte ToS (type of service) field. Compare IP precedence value.

dynamic-access port. A port that is dynamically assigned to a VLAN by VMPS. Contrast with static-access port.

EIGRP. Enhanced Interior Gateway Routing Protocol. An advanced version of IGRP that provides superior convergence properties and operating efficiency, and combines the advantages of link-state protocols with those of distance-vector protocols.

Enhanced Interior Gateway Routing Protocol. See EIGRP.

EtherChannel. A group of Fast Ethernet or Gigabit Ethernet ports that acts as a single logical port for high-bandwidth connections between switches or between switches and servers. If a port within an EtherChannel fails, traffic previously carried over the failed port switches to the remaining ports within the EtherChannel.

expert mode. Interacting with the user interface by selecting options and using entry fields in a configuration window. You request expert mode by selecting the Expert button below the menu bar. Contrast with guide mode.

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failover. The transfer of responsibilities to a standby switch.

Fast Leave. A multicast routing feature that speeds up the removal of a multicast group from a router. When a member leaves a group, Fast Leave searches for other members of the group (devices receiving IP multicast packets from a particular port on the switch). If there are no other members on the port, the switch removes the port from the group. If there are no other ports in the group, the switch notifies the routers connected to the VLAN to delete the entire group.

guide mode. Interacting with the user interface by responding to a series of incremental steps. You request guide mode by selecting the Guide button below the menu bar. Contrast with expert mode.

Hot Standby Routing Protocol. See HSRP.

HSRP. Hot Standby Routing Protocol. A protocol that provides high network availability and transparent network topology changes. It creates a device group with a lead device that services all the packets sent to a hot standby address. The lead device is monitored by others in the group; if it fails, one of the other devices inherits the lead position and the hot standby address.

IGMP. Internet Group Management Protocol. A protocol used between hosts on a LAN and routers on the LAN to determine which multicast groups the hosts belong to.

IGMP snooping. The examination by a Layer 2 switch of some Layer 3 information in an IGMP packet sent from a host to a router. The switch determines from its findings whether to add or remove member ports.

IGRP. Interior Gateway Routing Protocol. An Interior Gateway Protocol that addresses issues associated with routing in large, heterogenous networks.

Immediate Leave. A multicast routing feature that speeds up the removal of a multicast group from a router. When a member indicates that it wants to leave the group, Immediate Leave removes the member port from the group at once.

Interior Gateway Protocol. An Internet protocol that is used to exchange routing information within an autonomous system.

Interior Gateway Routing Protocol. See IGRP.

Internet Group Management Protocol. See IGMP.

IP phone. A full-featured telephone that provides voice communication over an IP network.

IP precedence value. In a packet, the three most significant bits of the 1-byte ToS (type of service) field. Compare DSCP value.

ISL. Inter-Switch Link. A Cisco-proprietary protocol that maintains VLAN information as traffic flows between switches and routers.

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LED polling interval. The frequency with which CMS polls the ports in the cluster and displays changes in the LED colors of ports. Compare network polling interval.

link-state protocol. A type of routing protocol that maintains a map of the internetwork, allowing it to see alternate routes or parallel paths for load balancing. OSPF is an example of this protocol type. Contrast with distance-vector protocol.

LRE. Long-Reach Ethernet. The technology used on Catalyst 2900 LRE XL switches to transfer data and voice traffic over standard telephone lines without Ethernet cabling. See also LRE profile.

LRE profile. A file that specifies the upstream and downstream transmission rates on an LRE link.

management VLAN. The VLAN to which the ports of the command, member, and candidate switches are connected, making management of the switch cluster possible.

mask. The part of an ACE that identifies the fields in a packet header that the ACE is matched against. Also referred to as an ACP.

member switch. A switch that belongs to a cluster and is accessed through a command switch.

multicast router port learning method. The protocol used to identify multicast router ports. With IGMP snooping, either CGMP or PIM-DVMRP (the default) can be used.

multicast routing. A routing technique that allows copies of a single packet to be passed to a selected subset of all possible destinations. Contrast with unicast routing.

native VLAN. The VLAN that carries untagged packets from an 802.1Q trunk port.

neighbor switch. A device that is detected by CDP but is ineligible to be a member switch.

network polling interval. The frequency with which CMS polls the command switch to determine the status of the cluster and the existence of new members. Compare LED polling interval.

network port. A port to which the switch forwards all VLAN traffic with unknown destination addresses. It is a means of preventing flooding to all the ports in a VLAN.

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Open Shortest Path First. See OSPF.

OSPF. Open Shortest Path First. A link-state protocol that imposes no limit on hop count, propagates routing changes instantaneously, supports variable-length subnet masks, and allows for load balancing based on the actual cost of the link. It also compartmentalizes networks into smaller regions called areas, which limits the traffic caused by link-state updates.

PAgP. Port Aggregation Protocol. A protocol that facilitates the automatic creation of EtherChannels by exchanging packets between Ethernet interfaces. It dynamically groups similarly configured interfaces into a single logical link.

parent window. A configuration window that is launched by choosing an option on the menu bar or clicking an icon on the toolbar. Contrast with child window.

PIM dense mode. An operational mode in which packets are forwarded on all outgoing interfaces until pruning and truncation occurs. Receivers are densely populated, and it is assumed that the downstream networks want to receive and will probably use the datagrams that are forwarded to them. The cost of using dense mode is its default flooding behavior. Compare with PIM sparse mode and PIM sparse-dense mode.

PIM sparse-dense mode. An operational mode in which an interface is treated as dense mode if the multicast group is in dense mode, and treated as sparse mode if the multicast group is in sparse mode. A group is sparse if the router knows about an RP for the group.

PIM sparse mode. An operational mode in which data is distributed to the minimal number of routers in the network. Packets are sent only if they are explicitly requested at the RP (rendezvous point). Receivers are widely distributed, and it is assumed that downstream networks will not necessarily use the datagrams that are sent to them. The cost of using sparse mode is its reliance on the periodic refreshing of explicit join messages and its need for RPs. Compare with PIM dense mode and PIM sparse-dense mode.

policer. A QoS specification that contains a maximum permissible rate of transmission, a maximum burst size for transmissions, and an action to take if either maximum is exceeded. See also aggregate policer.

policy. A set of one or more QoS classes and their associated policers.

Port Aggregation Protocol. See PAgP.

process ID. A number that identifies a group of networks that operate under the same set of administrative rules and share a common routing strategy.

Protocol-Independent Multicast. See PIM.

quality of service. See QoS.

queue threshold. The point of fullness at which packets are dropped from a queue. In QoS, egress queues have two thresholds, a low one at which ordinary packets are dropped, and a high one at which even high-priority packets are dropped. The types of packets that are dropped at each point are designated by DSPC numbers.

QoS. quality of service. The ability of a network or device to provide preferential service to selected traffic.

redundant uplink topology. An IP telephony configuration in which one or more access-level devices are connected to more than one backbone device. Compare star topology and U topology.

rendezvous point. See RP.

RIP. Routing Information Protocol. The most common Interior Gateway Protocol in the Internet. It uses a hop count as a routing metric.

root port. The switch port with the best path to the root switch.

root switch. The switch selected to be the center of a spanning tree topology. All dataflow across the network is from the perspective of this switch. See also root port.

routable interface. A routed port or an SVI.

routed port. A non-VLAN port that serves as a router interface.

route summarization. A routing protocol feature that reduces a number of link advertisements into a single summary advertisement.

Routing Information Protocol. See RIP.

routing protocol. A set of rules and conventions for gathering information about available networks, like the distance or cost to reach them, and determining the routing path for a packet.

RP. rendezvous point. A router specified in implementations of PIM sparse mode to track membership in multicast groups and to forward messages to multicast group addresses.

rules. The contents of a mask that are used for matching fields in a packet header.

shaping. The process of delaying out-of-profile packets so that they conform better to a profile. It is done at the egress from a network device (switch or router), as opposed to policing, which is done at ingress. It may be required even if traffic has been policed because of merging and branching flows within the device.

source-based forwarding. The forwarding of a packet by a port group based on the packet source address. Contrast with destination-based forwarding.

Spanning Tree Protocol. See STP.

standard DSCP values. A subset of DSCP values whose priorities have been agreed to by convention. They are: 10, 12, 14, 18, 20, 22, 26, 28, 30, 34, 36, 38, and 46. A higher value represents a higher priority.

star topology. An IP telephony configuration in which each access-level device is connected to a common backbone device. Compare redundant uplink topology and U topology.

static-access port. A port that is manually assigned to a VLAN. Contrast with dynamic-access port.

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STP. Spanning Tree Protocol. A standardized technique for maintaining a network of multiple bridges or switches. When a network topology changes, STP avoids the creation of loops by transparently reconfiguring bridges and switches, and places ports in a forwarding or blocking state. Each VLAN is treated as a separate bridge, and a separate instance of STP is applied to each.

supernet. A network under which other networks are aggregated. The aggregated networks are not advertised, nor do their addresses exist in backbone routing tables.

SVI. switch virtual interface. A VLAN with an assigned IP address that Layer 3 devices use to access the VLAN. An SVI can be configured to route packets from one VLAN to another.

switch virtual interface. See SVI.

traffic shaping. See shaping.

trunk port. A port that carries the traffic of multiple VLANs. Contrast with access port.

unicast routing. A routing technique that routes a packet to a single destination and uses a routing protocol to determine the path to that destination. Contrast with multicast routing.

U topology. An IP telephony configuration in which access-level devices are connected in a chain whose ends are connected to backbone devices. Compare star topology and redundant uplink topology.

variance multiplier. A number that is multiplied by the cost of the lowest-cost path. It is used in unequal-cost routing to eliminate paths from consideration whose cost exceeds the multiplied cost.

virtual LAN. See VLAN.

VLAN. A logical rather than a physical LAN comprising workgroups drawn together for business reasons or for a particular project, irrespective of each member's actual location.

VLAN map. An object that controls packets that are switched within a VLAN. When you attach a VLAN map to a VLAN, it directs the VLAN to forward or drop traffic from specific IP or MAC addresses.

VLAN Membership Policy Server. See VMPS.

VLAN Trunking Protocol. See VTP.

VMPS. VLAN Membership Policy Server. A switch that responds to a VQP request for a VLAN assignment for an end station. It assigns a VLAN to a dynamic-access port.

voice VLAN. A VLAN that is used by a switch for voice traffice from IP phones.

VTP. VLAN Trunking Protocol. A Layer 2 messaging protocol that maintains VLAN configuration consistency by managing the addition, deletion, and renaming of VLANs on a network-wide basis.

VTP pruning. The blockage of flooded broadcast, multicast, and unknown unicast traffic to VLANs on trunk ports that are included in the pruning-eligible list.

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