The region in which a failure has occurred in a token ring. When a station gains information that a serious problem, such as a cable break, has occurred with the network, it sends a beacon frame that includes the station reporting the failure, its Next Addressable Upstream Neighbor (NAUN), and everything between. This defines the failure domain. Beaconing then initiates the procedure known as auto-reconfiguration. See also: auto-reconfiguration and beacon.
In ATM networks, this mechanism is used for scouting a path if it isn't possible to locate one by using customary methods. The device relaxes requirements for certain characteristics, such as delay, in an attempt to find a path that meets a certain set of the most important requirements.
Fast EtherChannel uses load distribution to share the links called a bundle, which is a group of links treated as a single link. Should one link in the bundle fail, the Ethernet Bundle Controller (EBC) informs the Enhanced Address Recognition Logic (EARL) ASIC of the failure, and the EARL in turn ages out all addresses learned on that link. The EBC and the EARL use hardware to recalculate the source and destination address pair on a different link.
Any Ethernet specification with a speed of 100Mbps. FastEthernet is 10 times faster than 10BaseT, while retaining qualities such as MAC mechanisms, MTU, and frame format. These similarities make it possible for existing 10BaseT applications and management tools to be used on FastEthernet networks. FastEthernet is based on an extension of IEEE 802.3 specification (IEEE 802.3u). Compare to: Ethernet. See also: 100BaseT, 100BaseTX, and IEEE.
A Cisco feature that uses a route cache to speed packet switching through a router. Compare to: process switching.
Fiber Distributed Data Interface: A LAN standard, defined by ANSI X3T9.5, that can run at speeds up to 200Mbps and uses token-passing media access on fiber-optic cable. For redundancy, FDDI can use a dual-ring architecture.
Frequency-Division Multiplexing: A technique that permits information from several channels to be assigned bandwidth on one wire based on frequency. Contrast with: ATDM, TDM, and statistical multiplexing.
Forward Explicit Congestion Notification: A bit set by a Frame Relay network that informs the DTE receptor that congestion was encountered along the path from source to destination. A device receiving frames with the FECN bit set can ask higher-priority protocols to take flow-control action as needed. Contrast with: BECN.
FastEthernet Interface Processor: An interface processor employed on Cisco 7000 series routers, supporting up to two 100Mbps 100BaseT ports.
A barrier purposefully erected between any connected public networks and a private network, made up of a router or access server or several routers or access servers, that uses access lists and other methods to ensure the security of the private network.
The default mechanism for servicing data in a queue is usually based on the first in, first out (FIFO) principle.
electronically erasable programmable read-only memory (EEPROM). Used to hold the Cisco IOS in a router by default.
Developed by Intel and licensed to other semiconductor manufacturers, it is non-volatile storage that can be erased electronically and reprogrammed, physically located on an EEPROM chip. Flash memory permits software images to be stored, booted, and rewritten as needed. Cisco routers and switches use flash memory to hold the IOS by default. See also: EPROM and EEPROM.
A network that is one large collision domain and one large broadcast domain.
When traffic is received on an interface, it is then transmitted to every interface connected to that device except the interface from which the traffic originated. This technique can be used for traffic transfer by bridges and switches throughout the network.
A shortcut or MLS cache entry that is defined by the packet properties. Packets with identical properties belong to the same flow. See also: MLS.
A methodology used to ensure that receiving units are not overwhelmed with data from sending devices. Pacing, as it is called in IBM networks, means that when buffers at a receiving unit are full, a message is transmitted to the sending unit to temporarily halt transmissions until all the data in the receiving buffer has been processed and the buffer is again ready for action.
The decision-making process that a switch goes through to determine which ports to forward a frame out of.
Frame Relay Access Device: Any device affording a connection between a LAN and a Frame Relay WAN. See also: Cisco FRAD and FRAS.
Any portion of a larger packet that has been intentionally segmented into smaller pieces. A packet fragment does not necessarily indicate an error and can be intentional. See also: fragmentation.
The process of intentionally segmenting a packet into smaller pieces when sending data over an intermediate network medium that cannot support the larger packet size.
LAN switch type that reads into the data section of a frame to make sure fragmentation did not occur. Sometimes called 'modified cut-through.'
A logical unit of information sent by the Data Link layer over a transmission medium. The term often refers to the header and trailer, employed for synchronization and error control, that surround the data contained in the unit.
A more efficient replacement of the X.25 protocol (an unrelated packet relay technology that guarantees data delivery). Frame Relay is an industry-standard, shared-access, best-effort, switched Data-Link layer encapsulation that services multiple virtual circuits and protocols between connected mechanisms.
Defined in RFC 1490, this bridging method uses the identical spanning-tree algorithm as other bridging operations but permits packets to be encapsulated for transmission across a Frame Relay network.
A process that occurs when a router at a service provider provides packet switching for Frame Relay packets.
VLANs can span multiple connected switches, which Cisco calls a switch- fabric. Switches within this switch-fabric must keep track of frames as they are received on the switch ports, and they must keep track of the VLAN they belong to as the frames traverse this switch-fabric. Frame tagging performs this function. Switches can then direct frames to the appropriate port.
Encapsulation at the Data Link layer of the OSI model. It is called framing because the packet is encapsulated with both a header and a trailer.
Frame Relay Access Support: A feature of Cisco IOS software that enables SDLC-, Ethernet-, Token Ring-, and Frame Relay-attached IBM devices to be linked with other IBM mechanisms on a Frame Relay network. See also: FRAD.
The number of cycles of an alternating current signal per time unit, measured in hertz (cycles per second).
Fast Serial Interface Processor: The Cisco 7000 routers' default serial interface processor, it provides four or eight high-speed serial ports.
File Transfer Protocol: The TCP/IP protocol used for transmitting files between network nodes, it supports a broad range of file types and is defined in RFC 959. See also: TFTP.
The capacity to transmit information between a sending station and a receiving unit at the same time. See also: half duplex.
A type of network topology in which every node has either a physical or a virtual circuit linking it to every other network node. A full mesh supplies a great deal of redundancy but is typically reserved for network backbones because of its expense. See also: partial mesh.