Information Technology Reference
In-Depth Information
delay Metric that refers to how long it takes a packet to reach the destination. Depends on
many factors, such as link bandwidth, utilization, port queues, and physical distance traveled.
denial-of-service (DoS) attack Tr ie s to over whelm re s ource s s uch as memor y, CPU, and
bandwidth, thus impacting the attacked system and denying legitimate users access.
device virtualization
Allows for a single physical device to act like multiple copies of itself.
DHCP Dynamic Host Configuration Protocol. Used to dynamically configure IP parameters
on hosts on the network.
DHCP snooping Ve r i f i e s D H C P t r a n s a c t i o n s a n d p r e v e n t s r o g u e D H C P s e r v e r s f r o m i n t e r -
fer ing w ith produc t ion t raffic.
DHCPv6
Dynamic Host Configuration Protocol Version 6.
dial backup
ISDN provides backup dialup services in the event of a failure of a primary
WA N c i r c u i t .
digital subscriber line (DSL) A technology that provides high-speed Internet data services
over ordinary copper telephone lines.
distance vector
Routing protocols that advertise the entire routing table to its neighbors.
distribution layer Provides policy-based connectivity and aggregation of access layer
devices. Isolation point between access and core layers. At this layer, security filtering, aggre-
gation of wiring closets, QoS, and routing between VLANs occur.
DNS Domain Name Service. A distributed database system that returns the destination IP
addresses given a domain name.
DR Designated router. OSPF router on multiaccess networks (Ethernet) that is selected to
collect all LSAs for the multiaccess network.
DSCP Differentiated services code point. Uses 6 bits in the ToS field to support differentiat-
ed services.
DSSS
Direct sequence spread spectrum.
DUAL Diffusing Update Algorithm. Used by EIGRP to select paths and guarantee freedom
from routing loops.
DWDM Dense wavelength-division multiplexing. Increases fiber optics bandwidth capabili-
ties by using different wavelengths of light called channels over the same fiber strand.
Dynamic ARP inspection
Intercepts ARP packets and verifies that the packets have valid IP-
to-MAC bindings.
E&M
Ear and Mouth; analog trunk.
EGP Exterior gateway protocol. Used to communicate routing information with external
networks.
EIGRP
Enhanced Interior Gateway Routing Protocol. Cisco proprietary routing protocol
paths and guarantee freedom from routing loops.
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