Cloned from: CCNA Vocabulary



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Punchdown block
A device that connects telephone or data lines to each other. The solid copper wires are punched down into short open-ended slots to establish connectivity.
  CPE
Customer Premise Equipment Terminating equi0pment, such as terminals, telephones, and modems, supplied by the telephone company, installed at a customer site, and connected to the telephone company network.
Interface
1) Connection between two systems or devices. 2) In routing terminology, a network connection. 3) In telephony, a shared boundary devined by common physical interconnection characteristics, signal characteristics, and meanings of interchanged signals. 4) the boundary between adjacent layers of the OSI model
Default Gateway
Path of a packet on a network used by default, or as the gateway of last resort, when the destination hosts are not listed in the routing table.
Form Factor
Physical size and shape of computer components. Components that share the same form factor are physically interchangeable.
Out-of-band
Transmission using frequencies or channels outside the frequencies or channels normally used for information transfer. Out-of-band signaling is often used for error reporting in situations in which in-band signaling can be affected by whatever problems the network might be experiencing.
In-band
Management technique for connecting a computer to a network device. In-band management is used to monitor and make configuration changes to a network device over a network connection.
Port density
Amount of ports per RU on a switch
Wire speed
Rate that packets are forwarded on a network.
VLAN
Virtual Local Area Network Group of devices on a network, typically end-user stations, that communicate as if attached to the same network segment even though they may be on different segments. VLANs are configured on workgroup switches. Switches with VLANs may interconnect using VLAN trunking protocols.
CAM
Content Addressable Memory MAC address table maintained by a switch. A CAM is recreated every time a switch is activated.
Aging timer
Period of time in which an entry must be used before a switch deletes it from the MAC address table.
Unicast
Type of message sent to a single network destination.
Floods
Technique used by switches to pass traffic that is received on an interface to all other interfaces of the device except the interface on which the information was originally received.
Broadcast
Set of devices that receive broadcast frames originating from any of the devices within the set. A broadcast domain is typically bounded by routers because routers do not forward broadcast frames.
Collision Domain
Network area in Ethernet where frames that have collided are propagated. Repeaters and hubs have collision domains. LAN switches, bridges, and routers do not.
Microsegmentation
Division of a network into smaller segments, usually with the intention of increasing aggregate bandwidth to network devices.
VC
Virtual Circuit Logical relationship created to ensure reliable communication between two network devices. A virtual circuit is defined by a virtual path identifier/virtual channel identifier pair, and can be either a permanent virtual circuit or switched virtual circuit. Virtual circuits are used in Frame Relay and X.25. In ATM, a virtual circuit is called a virtual channel.
Asymmetric
When one function on a network takes a greater length of time than the reverse function. An example of an asymmetric function is the compression and decompression of data.
Uplink Ports
High-speed port that connects to areas that have a higher demand for bandwidth, such as another switch, a server farm, or other networks.
Microprocessor
Chip that contains the central processing unit for the device.
Multilayer Switching
Device that filters and forwards packets based on MAC addresses and network addresses. A layer 2/ layer 3 switch is a multilayer switch.
ASIC
Application-specific Integrated circuit Circuit that gives precise instructions for the functionality of a device during Layer 3 switching.
Cache
Act of storing data, or the location of stored data.
Store and forward Packet Switching
Technique in which frames are completely processed before being forwarded out of the appropriate port. Store and forward packet switching is a process that includes the calculation of the cyclic redundancy check and the verification of the destination address.
Cut-through switching
Process where data is streamed through a switch so that the leading edge of a packet exits the switch at the output port before the packet finishes entering the input port. Cut-through packet switching enables a device to read, process, and forward packets as soon as the destination address is looked up, and the outgoing port determined. Cut-through packet switching is also known as on-the-fly packet switching. Contrast with store and forward packet switching.
CRC
Cyclic Redundancy Check Store and Forward error checking technique that counts the number of packets the checksum generates by far end device and compares it to the checksum calculated from the data received. A CRC error may indicate noise, gain hits, or transmission problems on the data link or interface.
FCS
Frame Check Sequence Characters added to a frame for error control purposes. FCS is used in HDLC, Frame Relay, and other Data Link Layer protocols
Fast-forward
Cut-through switching method where the switch forwards the frame before all of frame is received. Using the fast-forward method, the switch forwards the frame out of the destination port immediately when the destination MAC address is read. The switch does not calculate or check the CRC value. The fast-forward method has lowest latency but may forward collision fragments and damaged frames. This method of switching works best in a stable network with few errors.
Fragment-free
A switching technique that forwards a frame after the first 64 bytes are received. Fragment-free switching has a higher latency than fast-forward switching.
Runt
Frame that is less than 64 bytes, usually the result of a collision. In fragment-free switching, the switch reads the first 64 bytes of the frame before it begins to forward it out the destination port. Checkign the first 64 bytes ensures that the switch does not forward collision fragments.
Threshold value
Maximum number of errors that a switch allows before it will go into store and forwarding switching to slow traffic and correct the problem.
Adaptive Cut-through
Type of switching when the flow reverts back to fast-forward mode when the number of errors drops below the threshold value to an acceptable level.
Redundancy
1) Duplication of components on a network, such as devices, services, or connections, for the purpose of maintaining operability if any tools fails. 2) Portion of the total information contained in a message that can be eliminated without losing the contest.
Congestion
Traffic in excess of network capacity.
Availability
Condition of accessibility.
Switching loops
Causes duplicate frames to be sent throughout a network. A switching loop occurs when there is more than one path between two switches.
Broadcast storm
Undersirable network event in which many broadcasts are sent simultaneously across all network segments. A broadcast storm uses substantial network bandwidth and typically causes network time-outs.
Unicast Frames
Data packet that is addressed to a single destination
STP
Spanning Tree Protocol Bridge standards that use the spanning-tree algorithm and enable a bridge to dynamically work around loops in a network topology by creating a spanning tree. A bridge exchanges BPDU messages with other bridges to detect loops, and then removes the loops by shutting down bridge interfaces.
BPDU
Bridge Protocol Data Units STP hello packets that is sent out at configurable intervals to exchange information among bridges ni the network
Blocking
1) Condition in a switching system in which no paths are available to complete a circuit. 2) Condition when one activity cannot begin until another has been completed.
Listening
One of four states that a port cycles through when a switch powers on an STP network. The switch listens for BPDUs from neighboring switches.
Learning
One of four states that a port cycles through when a switch powers on an STP network. The switch uses information learned to forward a packet.
Forwarding
Process of sending a frame out of a port toward the destination by way of an internetworking device. Examples of devices that forward frames are hosts, repeaters, bridges, and routers.
Root Bridge
Also known as Root Switch Designated packet forwarding device in a spanning-tree implementation that receive topology information and notifies all other bridges in the network when topology changes are required. A root bridge prevents loops and provides a measure of defense against link failure.
Root Switch
Also known as Root Bridge Designated packet forwarding device in a spanning-tree implementation that receive topology information and notifies all other bridges in the network when topology changes are required. A root bridge prevents loops and provides a measure of defense against link failure.
BID
Bridge ID Identification of the root bridge which is the focal point in an STP network.
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